An important consideration when addressing safety issues is the incidence of pathogens and outbreaks associated with particular food products. This chapter addresses outbreaks that have been associated with the consumption of fresh and fresh-cut produce. In addition, studies that investigate the incidence of pathogens and factors contributing to the survival and growth of pathogens are reviewed. Although they may not be exhaustive, the tables at the end of the chapter include highlights of incidence studies from industry and published literature sources (Tables I1-I7), outbreaks (Tables O1-O10), and growth/survival studies related to fresh produce (Tables G/S1-G/S8).
1. Foodborne pathogens associated with fresh produce
The minimum processing required for fresh and fresh-cut produce, which omits any effective microbial elimination step, results in food products that naturally would carry microorganisms, some of which may be potentially hazardous to human health. When investigating possible control methods, a vital step is to examine the nature of the human pathogenic microorganisms present in produce throughout the production process. However, incidence studies are time-consuming and expensive. For this reason, sample sizes are often too small to be of statistical relevance, especially if the probability of detection is low. Most researchers do not collect sufficient information regarding the source of the sample other than perhaps the country of origin or sample location (for example, retail outlets, farmers' markets). There has been little consistency in sample collection, treatment, laboratory test methods, or data analysis. Controls are often missing and techniques for isolating pathogens from produce items are often not optimized. In many cases, identification of the pathogen has not been verified. Most published articles stress the detection of pathogens in incidence surveys; negative data may not be reported or their significance is minimized. However, these negative data are important in evaluating the risks associated with consumption of fresh fruits and vegetables and should be considered in risk assessments. Table IV-1 outlines some of the factors that should be considered when designing a study to determine the frequency of isolation of pathogens from produce.
Because of the extremely large number of variables that might influence contamination of raw fruits or vegetables, it is difficult to design well-controlled experiments that would address risk factors for contamination. While incidence studies can provide a snapshot assessment of contamination at a particular location on a particular produce item at a particular time of year, they rarely provide information on the source of contamination. For these reasons, caution must be used when interpreting data from these types of studies, and overly broad conclusions should be avoided. Nevertheless, numerous pathogenic microorganisms have been isolated from a wide variety of fresh fruits and vegetables, sometimes at relatively high frequencies (Table I1-I7). Not all of the microorganisms listed in these tables have been linked to produce-associated illnesses. Under the right conditions, however, all of these microorganisms have the potential to cause produce-associated illness. Isolation rates are not consistent. Percentage of samples contaminated ranges from 0 to greater than 50%, depending upon the target pathogen and produce item. Data provided by Wells and Butterfield (1997) indicate that Salmonella is more readily isolated from decaying fruits and vegetables. Whether this applies to other pathogens is not known.
Table IV-1. Considerations when examining raw fruits and vegetables for the presence and populations of pathogenic microorganisms
Procedure for sampling
Location of source (field, packing shed, processing plant, retail location, food service, home)
Number and size of samples
Distribution of samples in test lot
Protection of samples for transport to laboratory
Handling samples between collection and analysis
Protection against cross-contamination
Temperature between selection and analysis of sample
Time between selection and analysis of samples
Weight or number of pieces to represent samples
Area or portion to be tested (whole piece, skin only, diced, cut)
Selection of wash fluid or diluent
Ratio of produce to wash fluid or diluent
Temperature of produce and wash fluid or diluent
Soaked or not soaked before processing
Type of processing (washing, rubbing, stomaching, homogenizing, macerating, blending)
Time of processing
Enrichment and/or direct plating
Composition and volume of enrichment broth
Composition of direct plating medium
Pour-plate or surface plate
Incubation temperature and time
2. Outbreaks of foodborne illness associated with the consumption of raw fruits and vegetables
The number of foodborne illness outbreaks linked to fresh produce and reported to the United States Centers for Disease Control and Prevention (CDC) has increased in the last years (Bean and Griffin 1990; CDC 1990; CDC 2000). Some of this increase is due to improved surveillance, but other factors may also come into play. A number of reasons have been proposed for this increased association of foodborne illness with fresh produce. Since the early 1970's, a significant increase in the consumption of fresh produce has been observed in the United States, presumably due, in part, to active promotion of fruits and vegetables as an important part of a healthy diet. From 1982 to 1997, per capita consumption of fresh fruits and vegetables increased from 91.6 to 121.1 kg, an increase of 32% (Table IV-2). If contamination levels were consistent, increased consumption of these foods should be expected to lead to greater numbers of illnesses over this time. During this same period, there has been a trend toward greater consumption of foods not prepared in the home and an increase in the popularity of salad bars (buffets). Greater volumes of intact and chopped, sliced or prepared fruits and vegetables are being shipped from central locations and distributed over much larger geographical areas to many more people (see Chapter I). This, coupled with increased global trade, potentially increases human exposure to a wide variety of foodborne pathogens and also increases the chances that an outbreak will be detected. Reasons for increases in foodborne illness in the summertime are not fully understood, although abusive temperatures and a higher consumption of fresh produce during the summer months are likely to play a role.
Table IV-2. Per capita (kg) consumption of raw fruits and vegetables in the US. Source: Fruit and Tree Nut Situation and Outlook Report (USDA 1999).
The perishability of produce and a complex distribution system have made it difficult to effectively investigate many produce-related outbreaks. Trace-back has been particularly difficult because of the complexity of the distribution system and the practice of co-mingling produce in packing houses. Epidemiological investigations often take weeks before detecting a link between reported illnesses and a produce item. As a result, there is little or no product available for testing. However, improvements in outbreak investigations and pathogen detection methods have contributed to an increase in documentation of produce-borne illnesses.
Foodborne illness resulting from the consumption of any food is dependent upon a number of factors. The produce must first be contaminated with a pathogen and the pathogen must survive until the time of consumption at levels sufficient to cause illness. The infective dose (minimum numbers of organisms necessary to cause illness) is very low in many cases (Table IV-3), which means that the microorganism needs only to contaminate the food to survive without reproducing. For example, pathogenic parasites and viruses are unable to multiply outside of a human or animal host and only need to survive in sufficient numbers to cause illness.
Table IV-3. Characteristics of some microbial pathogens that have been linked to outbreaks of produce-associated illness.
|Microorganism||Typical Incubation Period||Symptoms||Infectious Dose (Number of cells)||Source|
|Clostridium botulinum||Nausea, vomiting, fatigue, dizziness, dryness of mouth and throat, muscle paralysis, difficulty swallowing, double or blurred vision, drooping eyelids, and breathing difficulties||soil, lakes, streams, decaying vegetation, reptiles|
|Escherichia coli O157:H7||Bloody diarrhea, abdominal pain. Can lead to hemolytic uremic syndrome and kidney failure especially in children and the elderly||animal feces, especially cattle, deer and human; cross contamination from raw meat|
|Salmonella spp.||Abdominal pain, diarrhea, chills, fever, nausea, vomiting||animal and human feces; cross contamination from raw meat, poultry, or eggs|
|Shigella spp.||Abdominal pain, diarrhea, fever, vomiting||human feces|
|Listeria monocytogenes||Febrile gastroenteritis in healthy adults; may lead to spontaneous abortion or stillbirth in pregnant women; severe septicemia and meningitis in neonates and immunocompromised adults; mortality may be 20 to 40%||soil, food processing environments|
|Cryptosporidium spp.||Profuse watery diarrhea, abdominal pain, anorexia, vomiting||Animal and human feces|
|Cyclospora spp.||Watery diarrhea, nausea, anorexia, abdominal cramps (duration 7 to 40 d)||others? specific environmental sources unknown at this time|
|Hepatitis A||Fever, malaise, anorexia, nausea, abdominal pain, jaundice, dark urine||human feces and urine|
|Norwalk/Norwalk-like virus||Vomiting diarrhea, malaise, fever, nausea, abdominal cramps||human feces, vomitus|
In other cases, however, multiplication of the pathogen is also essential. Some microorganisms cause illness only when ingested in high numbers (for example, Clostridium perfringens), while in other cases, the infectious dose is thought to be dependent upon the susceptibility of the individual (most infectious agents). Illness due to Staphylococcus aureus, Bacillus cereus, or Clostridium botulinum is a result of the production of toxins in the food, and it is the toxins that are responsible (sometimes in the absence of viable cells) for symptoms of the disease. These toxins are only produced by multiplying cells. This requires favorable growth conditions. In summary, while enhancing the likelihood of illness, temperature abuse and multiplication of pathogenic bacteria is not always necessary for foodborne illness to occur. Although raw produce is often spoiled by other microorganisms prior to detection of toxin, one should not rely on this fact to prevent the development of disease (for example, botulism).
A wide variety of bacteria, viruses, and parasites have been linked to outbreaks of illness associated with fresh produce (Table O1-O10). Although these microorganisms are physiologically diverse, they share some common features (Table IV-3). Foodborne pathogens that are frequently associated with fresh produce originate, for the most part, from enteric environments - that is, they are found in the intestinal tract and fecal material of humans or animals. Exceptions include C. botulinum, which is usually isolated from soils, water and decaying plant or animal material, and Listeria monocytogenes, which can be readily isolated from human and animal feces, as well as from many other environments including soil, agricultural irrigation sources, decaying plant residue on equipment or bins, cull piles, packing sheds and food processing facilities.
Produce can become contaminated with microbial pathogens by a wide variety of mechanisms. Contamination leading to foodborne illness has occurred during production, harvest, processing, and transporting, as well as in retail and foodservice establishments and in the home kitchen (Table IV-4). Contamination at any point in the food handling chain can be exacerbated by improper handling and storage of produce prior to consumption (Table O10). The point of contamination is important because control measures will be most effective if geared towards reducing contamination at the source. For example, Good Agricultural Practices will not prevent illness due to post-harvest cross-contamination at any point, including foodservice environments or in the home (Table O9).
Contamination of raw fruits and vegetables with pathogenic organisms of human health significance can occur directly or indirectly via animals or insects, soil, water, dirty equipment, and human handling. For example, fruit flies have been shown to transfer Escherichia coli O157:H7 to damaged apples under laboratory conditions (Janisiewicz and others 1999). This may have implications during harvesting and in packing sheds or processing facilities, where damaged produce is inevitable and flies may be difficult to control. Humans and animals can shed foodborne pathogens in the absence of signs of illness. While domestic animals may be separated from fruit and vegetable growing operations, wild animals and birds can only be controlled to a limited extent. Human hygiene, including hand washing all along the food chain, is critical in reducing or eliminating contamination with fecal pathogens.
Table IV-4. Sources of pathogenic microorganisms on fresh produce and conditions that influence their survival and growth
Green or inadequately composted manure
Wild and domestic animals
Water for other uses (for example, pesticides, foliar treatments, growth hormones)
Human handling (workers, consumers)
Transport containers (field to packing shed)
Wild and domestic animals
Wash and rinse water
Sorting, packing, cutting and further-processing equipment
Improper storage (temperature, physical environment)
Improper packaging (includes new packaging technologies)
Cross contamination (other foods in storage, preparation and display areas)
Improper display temperature
Improper handling after wholesale or retail purchase
Cooling water (for example, hydrocooling)
3. Survival and multiplication of pathogens on raw produce
The survival and/or growth of pathogens on fresh produce is influenced by the organism, produce item, and environmental conditions in the field and thereafter, including storage conditions. In general, pathogens will survive but not grow on the uninjured outer surface of fresh fruits or vegetables, due in part to the protective character of the plant's natural barriers (for example, cell walls and wax layers). In some cases pathogen levels will decline on the outer surface.
In the field, the physical environment of leaf surfaces is considered to be inhospitable for the growth and survival of bacteria (for example, lack of nutrients and free moisture, temperature and humidity fluctuations, and ultraviolet light) (Dickinson 1986). Environmental conditions, however, can greatly influence bacterial populations; the presence of free moisture on leaves from precipitation, dew, or irrigation may promote survival and growth of bacterial populations (Blakeman 1981; Andrews 1992; Beattie and Lindow 1995, 1999). Certain conditions, such as sunlight, particularly the shorter ultraviolet wavelengths, can damage bacterial cells (Webb 1976; Jagger 1981; Sundin and others 1996; Sundin and Jacobs 1999). Consequently, nature may select for bacteria with adaptations to these stressful conditions. Although most of the body of research has been done with stress adaptation of microorganisms other than human pathogens (high ultraviolet tolerance in Pseudomonas syringae or high osmotic potentials in Escherichia herbicola) preliminary results suggest that humans pathogens are less likely to develop stress resistance (O'Brien and Lindow 1988). Many of the human pathogens have an enteric source, and therefore may be unsuccessful as plant colonists relative to the more suited plant microbial populations. The relative fitness of human pathogens and common epiphytes (microbes that grow and persist on plant surfaces) and the interaction between bacterial pathogens and indigenous microflora needs further research.
Similarly, after harvest, pathogens will survive but not grow on the outer surface of fresh fruits and vegetables, especially if the humidity is high. In some cases, pathogen levels will decline on the outer surface. The rate of decline is dependent upon the produce type, humidity, and temperature, as well as the atmosphere and type of packaging used. Growth on intact surfaces is not common because foodborne pathogens do not produce the enzymes necessary to break down the protective outer barriers on most produce. This restricts the availability of nutrients and moisture. One exception is the reported growth of E. coli O157:H7 on the surface of watermelon and cantaloupe rinds (Table G/S1).
Survival of foodborne pathogens on produce is significantly enhanced once the protective epidermal barrier has been broken either by physical damage, such as punctures or bruising, or by degradation by plant pathogens (bacteria or fungi). These conditions can also promote the multiplication of pathogens, especially at nonrefrigerated temperatures. Microorganisms often survive at refrigerated temperatures even though these conditions reduce or eliminate the ability of the organisms to multiply. Exceptions to this are the psychrotrophic pathogens including non-proteolytic C. botulinum, L. monocytogenes, Y. enterocolitica, and the presumptive pathogen Aeromonas hydrophila. Various enteric pathogens have been shown to multiply on the surface of cut melons, on shredded lettuce, and on chopped parsley and under acidic conditions, such chopped tomatoes and wounded apple tissue (Tables G/S1 Â– G/S8). Temperature control becomes critical for preventing bacterial reproduction on any cut produce item. Fresh-cut produce, by definition, has been injured through peeling, cutting, slicing, or shredding. These same operations can transfer pathogenic microorganisms, if present, from the surface of the intact fruit or vegetable to the internal tissues. Injured cells and released cell fluids provide a nourishing environment for microbial growth.
A vigorous population of nonpathogenic bacteria is potentially another barrier to reduce the risk of foodborne illness from fresh-cut products. These bacteria do not necessarily prevent the growth of pathogens but they do provide indicators of temperature abuse and age of the produce by causing detectable spoilage. Most pathogens do not cause produce to spoil, even at relatively high populations. In the absence of spoilage, high populations of pathogens may be achieved and the item may be consumed because it is not perceived as spoiled. For this reason, specifications requiring very low microbial counts may, in some cases, compromise produce safety.
Infiltration of wash-water into intact fruit has been demonstrated with several fruits and vegetables, and is thought to have contributed to an outbreak of salmonellosis associated with fresh market tomatoes (Table O8). Wash-water contaminated with microorganisms, including pathogens, can infiltrate the intercellular spaces through pores when conditions are right. Internal gas pressures and surface hydrophobicity usually prevent uptake of water. However, when the produce temperature is much higher than the water temperature, the pressure difference created may be sufficient to draw water into the fruit (Bartz 1999). Adding detergents to the water appears to enhance infiltration, likely due to reduced surface tension. Under some circumstances, wash water may enter an intact fruit through the stem scar or other opening, such as the blossom or stem end of an apple. Conditions that reduce infiltration of plant pathogens should also prevent infiltration of human pathogens.
3.1. Influence of packaging
Fresh produce packaged in gas-permeable films can modify its own atmosphere, thereby creating more favorable conditions for storage. Three mutually interacting processes determine the course of this modification: 1) respiration by the fruit or vegetable, 2) gas diffusion through the produce item, and 3) temperature, and 4) gas transmission through the film. As a result of produce respiration, the oxygen (O2) concentration in the package is decreased and the carbon dioxide (CO2) concentration is increased. Growth and toxin production by C. botulinum is of particular concern in this instance. This subject has been reviewed in depth (see Chapter VI).
3.2. Specific foods - Examples
Raw raspberries and possibly blackberries imported from Guatemala have been associated with several large Cyclospora cayetanensis outbreaks (Table O2). The natural host for this parasite has not been identified; however, contaminated water used for pesticide application and poor harvester hygiene has been suggested as the most likely routes of contamination. Frozen raspberries or frozen strawberries have been linked to two or three outbreaks of hepatitis A, respectively (Table O3). Hepatitis A, a virus spread by human feces, is thought to have contaminated the berries by contact with infected harvesters or contaminated irrigation water. Frozen raspberries have also been associated with illness due to calicivirus, also spread through human feces.
Raw berries destined for the fresh market are harvested by hand and field packed into retail containers without being washed. Strawberries destined for freezing are destemmed in the field, either using a metal device or a thumbnail. Berries which are to be processed are transported, usually at ambient temperature, to a processing facility where they are washed with potable water or water containing an antimicrobial (for example, chlorine), sometimes sliced, and often mixed with up to 30% sucrose before freezing. The extra human handling during harvesting and co-mingling in the processing facility may explain the greater association of outbreaks with frozen berries. Also, virus and parasites may actually be preserved by the freezing step.
To date, bacterial foodborne illnesses have not been linked to consumption of berries. However, reservoirs for enteric organisms such as Salmonella and E. coli O157:H7 are similar to that of hepatitis A virus, suggesting that bacterial pathogens may also be occasional contaminants of berries. A recent FDA survey of imported produce found Salmonella in one of 143 samples of strawberries (Table I1).
3.2.2. Seed sprouts.
Over the past several years, seed sprouts have become a fresh produce item commonly linked to foodborne illness. Seed sprouts are a special problem because bacterial pathogens that may be present at very low levels on sprout seeds at the time of sprouting can multiply to very high levels during the 3 to 10 d sprouting process and can survive through the typical refrigerated shelf life of the products (Table G/S 7). Also, seed sprouts are produced as agricultural commodities, not subject to sanitation requirements because they are not regarded as foods. A wide variety of pathogens have been isolated from sprouted seeds (Table I2). Outbreaks have been associated primarily with Salmonella serotypes but have also been attributed to B. cereus, E. coli O157:H7, and Y. enterocolitica (Table O4).
Most sprout outbreaks have been due to seed contaminated with a bacterial pathogen before the sprouting process begins, presumably during production or harvest (Table O4). Many pathogens can survive for months under the dry conditions used for seed storage. Populations in the seeds are exceptionally low, making it difficult to detect pathogens in routine seed screening programs (Table I2). Although contaminated alfalfa sprouts have been identified as the source of pathogens in many outbreaks, clover, radish, and mung bean sprouts have also been associated with outbreaks. The association with alfalfa sprouts may be due to the volume consumed, as these are the most popular type of seed sprouts that are commonly eaten raw. Mung bean sprouts, while sold in relatively large quantities are often stir-fried or otherwise heated prior to consumption. This would reduce the risk and likelihood of illness from mung bean sprouts. However, any type of sprout seed may potentially be contaminated with bacterial pathogens before it is sprouted.
Cut cantaloupe is considered a potentially hazardous food in the FDA Food Code because it is capable of supporting the growth of pathogens due to low acidity (pH 5.2 to 6.7) and high water activity (0.97 to 0.99). The FDA investigated the frequency of Salmonella isolated from cantaloupe imported from Mexico (Table I1). In 1990, 11 of 1,440 (0.76%) cantaloupe were positive for eight different Salmonella serotypes. In 1991, 24 of 2,220 (1.08%) were positive with 12 different Salmonella serotypes isolated. More recently, the FDA isolated Salmonella from eight (5.3%) and Shigella from three (2.0%) of 151 cantaloupe samples collected from nine countries exporting to the United States (FDA 2001). These results suggest that melons may be naturally contaminated with Salmonella.
Outbreaks of salmonellosis have been associated with the consumption of cut cantaloupe and watermelon (Table O1). At least two of these outbreaks have been relatively large and have involved multiple states and/or provinces. For most outbreaks, it has been assumed that Salmonella was present on the rind, presumably contaminated in the field or during washing in a packinghouse, and that the edible surface became contaminated during final preparation. Improper storage temperature combined with the favorable conditions for growth on the surface of cut melons were factors that likely contributed to the outbreak (Table O10). Some outbreaks associated with melons have resulted from contamination during final preparation either through an infected food handler (with, for example, Norwalk virus) or cross-contamination from raw beef to the melon (with, for example, E. coli O157:H7) via knives, cutting boards, or hands.
Escherichia coli O157:H7 and Salmonella, can survive and grow readily on improperly stored (non-refrigerated) cut melons (Table G/S1). When initial populations were between 2.0 and 3.0 log CFU/g, final levels reached 7.0 or 8.0 log CFU/g after 24 h at 23 °C (73.4°F). At 5 °C (41 °F), both Salmonella and E. coli O157:H7 populations did not increase.
Cut melons are subject to time/temperature requirements of the U. S. FDA model food code criteria for potentially hazardous food. Recommendations made by the FDA to retail establishments that prepare or sell fresh cantaloupe are that melons should be washed before cutting, clean, sanitized utensils and surfaces should be used when preparing cut melons, cut melons should be kept at or below 7 °C (44.6 °F), and they should be displayed for no longer than 4 h if they are not refrigerated (Golden and others 1993).
3.2.4. Unpasteurized juices.
Approximately 2% of all juices sold in the United States are unpasteurized. Parish (1997) provides an excellent review of the safety of unpasteurized fruit juices. Unpasteurized juices are made from fruits and vegetables that are ground and/or pressed or squeezed to extract the juice. Unpasteurized juices are included here because they have not been thermally processed and an evaluation of outbreaks associated with these products might contribute to an understanding of risk factors for contamination of the raw fruits.
There have been very few surveys of retail juices for the presence of pathogens, probably because of the very low probability of finding pathogens in these products. Sado and others (1998) used rapid test kits to survey retail juices for the presence of L. monocytogenes, E. coli O157:H7, Salmonella, coliforms, and fecal coliforms. Only L. monocytogenes was isolated from two of 50 juices, an apple juice (pH 3.78) and an apple raspberry blend (pH 3.75) (Table I1).
Although there is a long history of juice-related outbreaks, they have been relatively infrequent and, until 1995, were generally associated with very small commercial processors or home-prepared products (Table O5). While the acidity of most fruit juices prevents the multiplication of pathogens, survival is much better than has been traditionally assumed (Table G/S 6). Pathogen viability decreases with increasing temperature due to the rapid growth of yeasts and other spoilage organisms at the higher temperatures. This also leads to a decrease in shelf life.
While pathogen contamination routes have not been definitively confirmed in any juice outbreak, the use of dropped fruit, the use of non-potable water, and the presence of cattle, deer, or, in one case, amphibians, in or near the orchards or groves does appear to be a reoccurring theme. Of five documented outbreaks associated with reconstituted orange juice, three have been the result of contamination by an infected handler preparing the juice (Table O6). In another outbreak the water source used to reconstitute the juice was thought to be a factor.
3.3. Pathogens of concern Â– Bacteria
3.3.1. Aeromonas species
Aeromonas species were first recognized as pathogens of cold-blooded animals. The ability of Aeromonas hydrophila and Aeromonas sobria to cause human infection has not been fully confirmed, however, their potential as infectious agents exists (Wadstrom and Ljungh 1991). The presence of Aeromonas in drinking water, fresh and saline waters, brackish water and sewage has been demonstrated on a global scale. Cytotoxic strains have been isolated from a wide range of seafoods, meats and poultry as well as from seed sprouts, lettuce or salad greens, mixed raw vegetables, parsley, and carrots (Table I4, I5, I7); however, outbreaks associated with this organism have not been reported. The pathogen can grow rapidly on raw vegetables and seed sprouts at refrigeration temperature (Tables G/S4 and G/S7). Controlled or modified atmosphere storage does not significantly affect the growth of A. hydrophila.
3.3.2. Campylobacter species
Campylobacter jejuni and Campylobacter coli are a leading cause of bacterial enteritis. Campylobacter has been isolated from a variety of produce items sampled from farmer's markets in Canada and from mushrooms sampled from retail markets in the United States (Tables I4 and I6). While consumption of contaminated food of animal origin, particularly poultry, is largely responsible for infection, Campylobacter enteritis has also been associated with lettuce or salads (Table O7). Cross-contamination during food preparation was thought to be possible or probable, in one case with raw chicken juices (Table O7). Cross-contamination of fresh produce with Campylobacter from poultry and other meats is a distinct possibility in delicatessen and other foodservice operations. Therefore, the linkage of C. enteritis to uncooked produce should not be viewed as improbable; control should focus on reducing cross-contamination during food storage and preparation. Studies reported by Castillo and Escartin (1994) indicate that C. jejuni can survive on sliced watermelon and papaya for sufficient time to be a risk to the consumer (Tables G/S1 and G/S2).
3.3.3. Escherichia coli
Enterotoxigenic E. coli is a common cause of travelers' diarrhea, an illness sometimes experienced when visiting developing countries. Raw vegetables are thought to be a common cause of travelers' diarrhea. A prospective study of 73 physicians and 48 family members attending a conference in Mexico City in 1974 revealed that enterotoxigenic E. coli was the most common cause of illness (Merson and others 1976). Fifty-nine participants became ill from eating salads containing raw vegetables.
Outbreaks of illness determined to be caused by enterotoxigenic E. coli in persons who had not traveled outside the United States are not uncommon. In one outbreak, 47 airline passengers suffered from illness strongly associated with eating garden salad made from iceberg and romaine lettuce, endive, and shredded carrots (see Beuchat 1996b). In another outbreak, 78 lodge guests became ill after consuming tossed salad as part of a buffet dinner. The salad contained several ingredients, including onions, carrots, zucchini, peppers, broccoli, mushrooms, and tomatoes (see Beuchat 1996b).
Enterohemorrhagic E. coli O157:H7 is recognized as an important foodborne pathogen. The infectious dose is very low and sequelae to gastroenteritis can include bloody diarrhea (hemmorrhagic colitis) and hemolytic uremic syndrome. The latter is most common in young children (<5 years) and in the elderly. There have been very few surveys for the presence of the organism in raw produce. Surveys of lettuce or salad mixes in the United Kingdom and United States did not isolate the organism and, although originally included in an FDA imported produce study, it was later deleted because positive samples had not been identified (FDA 2001). However, a single survey in Mexico revealed very high isolation rates (19%) for this organism in mixed vegetables, cilantro, coriander, and celery (Table I5). This single study was published as an abstract in 1995 and, to our knowledge, has not been published as a peer reviewed manuscript. Therefore, we were unable to review their methodology.
Since cattle appear to be a primary reservoir, the vast majority of outbreaks of illness associated with E. coli O157:H7 have been associated with consuming undercooked beef and dairy products. However, outbreaks have also been linked to lettuce (Table O7), unpasteurized apple cider (Table O5), cantaloupe (Table O1), and sprouts (Table O4). In outbreaks associated with cantaloupe and in some cases lettuce, contamination, particularly with raw beef juices, occurred during final preparation (Table 09).
Escherichia coli O157:H7 grows rapidly in several types of raw fruits and vegetables, particularly when stored at 12°C (53.6°F) or above (Tables G/S1, G/S2, G/S4, G/S5, G/S7). Packaging under modified atmosphere has little or no effect on the survival or growth of E. coli O157:H7. In addition, the infection dose of E. coli O157:H7 is low and can develop acid-resistance.
3.3.4. Listeria monocytogenes
While L. monocytogenes causes relatively mild gastroenteritis in healthy adults, the illness can be severe in susceptible individuals including pregnant women, neonates, and immune compromised individuals. The infective dose for this organism has not been clearly established, although it is thought to be relatively low among susceptible individuals. Listeria monocytogenes is widely distributed on raw fruits and vegetables (Tables I2 and I4) and on plant material (Beuchat 1996b). However several studies with relatively large sample sizes failed to detect the organism (Table I4). Factors affecting its presence or persistence have yet to be determined. Plants and plant parts used as salad vegetables play a role in disseminating the pathogen from natural habitats to the human food supply. This role may be indirect, for example by contaminating milk via forage or silage, or direct in the form of raw contaminated produce. In 1967, Blenden and Szatalowicz (1967) reported that 731 cases of human listeriosis had been documented between 1933 and 1966 in the United States. They stated that produce such as lettuce or other fresh vegetables contaminated with L. monocytogenes may have been responsible for some of these cases. However, documented outbreaks associated with this organism and linked to fresh produce have been limited. Ho and others (1986), (Table O8), reported an outbreak of L. monocytogenes infection that involved 23 patients from eight Boston hospitals in 1979. Three foods (tuna fish, chicken salad and cheese) were preferred by case patients more frequently than by control patients. However, the only common foods served with these foods were raw celery, tomatoes, and lettuce. It was concluded that consumption of these vegetables may have caused the listeriosis outbreak. No attempt was made to isolate L. monocytogenes from vegetables at the time of the outbreak.
An outbreak of human infection due to L. monocytogenes occurred in 1981 in the Maritine provinces (Prince Edward Island, Nova Scotia and New Brunswick) in Canada (Table O8). A case-control survey revealed that cases were more likely than controls to have consumed coleslaw during the three months before onset of illness. Ingestion of radishes was associated with coleslaw consumption but not with illness. Coleslaw obtained from the refrigerator of a patient was positive for L. monocytogenes serotype 4b, which was the epidemic strain and the strain isolated from the patient's blood. The coleslaw was commercially prepared with cabbage and carrots obtained from wholesalers and local farmers. Two unopened packages of coleslaw purchased from two different Halifax, Nova Scotia supermarkets yielded L. monocytogenes serotype 4b. Both packages of coleslaw were produced by the same processor. An investigation of the sources of cabbage revealed one farmer who, in addition to raising cabbage, maintained a flock of sheep. Two of his sheep had died of listeriosis in 1979 and 1981. The farmer used composted and fresh sheep manure in fields in which cabbage were grown. From the last harvest in October through the winter and early spring, cabbage was kept in a cold-storage shed. A shipment of cabbage from that shed during the period of the outbreak was traced to the implicated coleslaw processor. This information strongly suggests that the vehicle of the 1981 Canadian outbreak of listerosis was coleslaw.
Listeria monocytogenes can grow on fresh produce stored at refrigerated temperature. Growth on fresh-cut fruit as well as asparagus, broccoli, butternut squash, coleslaw and cauliflower, rutabaga stored at 4°C (39.2°F) (Table G/S4), lettuce at 5°C (41°F) (Table G/S5) and chicory endive at 6.5°C (43.7°F) (Table G/S4) has been reported. Controlled atmosphere storage does not appear to influence growth rates. Carrot juice appears to be inhibitory towards this organism (Beuchat and Brackett 1990a; Nguyen-the and Lund 1991, 1992; Beuchat and others 1994; Beuchat and Doyle 1995). The antimicrobial properties are attributed to phytoalexins naturally present in carrots. The addition of carrot juice as a natural antimicrobial in other food products has been relatively unsuccessful (Beuchat and Doyle 1995).
The genus Salmonella has over 2700 serotypes. Animals and birds are the natural reservoirs. Surveys of fresh produce have revealed the presence of several Salmonella serotypes capable of causing human infection (Table I1-I7).
Poultry and other meat products, eggs and dairy products, are the most commonly implicated sources in salmonellosis outbreaks. Fresh fruits and vegetables are implicated less frequently, although outbreaks have been documented most notably in cantaloupe and sprouts. Several additional large outbreaks of salmonellosis have been attributed to fresh produce. Among them are three multi-state outbreaks traced to the consumption of raw tomatoes; one involved Salmonella Javiana in 1992, another involved Salmonella Montevideo in 1993, and a third in 2000 involved Salmonella Baildon (Table O8). Subsequent laboratory studies revealed that the pathogen can grow in damaged, chopped, or sliced tomatoes (pH 4.1 Â– 4.5) stored at 20 to 30°C (68 to 86°F ) (Table G/S3).
3.3.6. Shigella species
The genus Shigella is composed of four species, Shigella dysenteriae, Shigella boydii, Shigella sonnei, and Shigella flexneri. All species are pathogenic to humans at a low dose of infection. Shigellosis is usually transmitted from person-to-person but may also occur by consumption of contaminated water and foods, including foods such as fruits or vegetables that have received little or no heat treatment. Several large outbreaks of shigellosis have been attributed to the consumption of contaminated raw vegetables. A lettuce processing facility was the common source of product responsible for outbreaks caused by S. sonnei that occurred simultaneously on two university campuses in Texas (Table O7). Ill students on both campuses had eaten salads from self-serve salad bars. Lettuce was the only produce item used in salads consumed by all students who became ill.
In another outbreak of S. sonnei gastroenteritis was associated with eating shredded lettuce (Table O7). All implicated restaurants received shredded lettuce from the same produce facility. An investigation suggested that a worker in the plant was the source of contamination and that the method of processing allowed contamination of the lettuce.
Two midwestern United States outbreaks of S. flexneri infection have been linked to the consumption of fresh green onions (see Beuchat, 1996b). The onions were traced to shippers in California who obtained most of their green onions from a single farm in Mexico. It was concluded that contamination may have occurred in Mexico at harvest or during packing.
Shigella sonnei can survive on lettuce at 5°C (41°F ) for 3 days without decreasing in number, and increased by more than 1000-fold at 22°C (71.6°F) (Table G/S5). Shigella can grow in shredded cabbage and chopped parsley stored at 24°C (75.2°F) (Table G/S4). Populations of S. sonnei, S. flexneri, and S. dysenteriae inoculated onto the surface of freshly cut cubes of papaya, jicama, and watermelon increased substantially within 4-6 h at 22-27°C (71.6-80.6°F) (Table G/S2, G/S4, and G/S1). The pH values of the three fruits were 5.69, 5.97 and 6.81, respectively.
3.3.7. Staphylococcus aureus
Staphylococcus aureus has been detected on fresh produce and ready-to-eat vegetable salads (Table I2 and I6), and is known to be carried by food handlers. However, enterotoxigenic S. aureus does not compete well with other microorganisms normally present on fresh produce, so incipient spoilage caused by nonpathogenic microbiota would likely precede the development of high populations of this pathogen. An outbreak of staphylococcal foodborne illness was linked to canned mushrooms. Growth and toxin production occurred prior to processing the mushrooms, without significant visual degradation, possibly because the mushrooms were held under ambient conditions in plastic bags and with salt. Conditions within the bags rapidly became anaerobic and the normal spoilage microbiota may have been inhibited and S. aureus selected. Because the toxin is heat stable, it survived the thermal process. This suggests that raw produce-associated outbreaks due to S. aureus could potentially occur given the right conditions. S. aureus has been shown to grow on peeled Hamlin oranges (Table G/S2) stored at 24°C (75.2°F) or survived up to 14 d when stored at 4-8°C (39.2-46.4°F).
3.3.8. Yersinia enterocolitica
Although animals, particularly swine, are the predominant natural reservoir for Y. enterocolitica, the pathogen has also been isolated from several raw vegetables. Yersinia enterocolitica infection has been associated with the consumption of mung bean sprouts contaminated with well-water containing the organism (Table O4). Catteau and others (1985) analyzed 58 samples of grated carrots obtained from eating establishments in France and found that 27% were contaminated with Yersinia. Seven percent of the samples contained Y. enterocolitica serotypes that may be pathogenic to humans. Darbas and others (1985) examined prepared raw vegetables destined for school meals that had been held for up to 5 days in cold storage. Fifty percent of 30 samples of raw vegetables analyzed contained Yersinia species. The incidence was higher in root and leafy vegetables than for tomatoes or cucumbers. Yersinia enterocolitica was the only species isolated from grated carrots, whereas Yersinia intermedia and Yersinia kristensenii were mainly isolated from lettuce. Cross-contamination between vegetables was observed in some cases. No pathogenic strains were isolated from raw vegetables analyzed in this study. The pathogen can grow at refrigeration temperatures commonly used during transport and storage of fresh produce.
3.4. Spore-forming pathogenic bacteria
Contamination of vegetables and fruits with spores of pathogenic bacteria such as B. cereus, C. botulinum, or C. perfringens present in soil is common (Tables I2, I4, I5, and I7). However, only when produce is handled in a manner that enables germination of spores and growth of vegetative cells is there a threat to public health from these spore-forming bacteria. Of particular concern are vegetables packaged under modified atmosphere (see Chapter VI).
Botulism has been linked more to consumption of cooked vegetables than to fresh produce. The organism requires relatively high water activity, a pH of greater than 4.6, relatively warm temperatures, and anaerobic conditions to grow and produce toxin. Growth and toxin production often lag behind spoilage in fresh vegetables. Of greatest concern are those products that will support growth and toxin production prior to visible signs of spoilage.
Outbreaks implicating cabbage and garlic in oil have been documented (Table O8-10). The garlic was likely dried and rehydrated prior to mixing with oil, but subsequent studies have shown that the organism will grow in fresh garlic. Botulism has been linked to eating coleslaw prepared from packaged, shredded cabbage mixed with coleslaw dressing (Solomon and others 1990). Since the pH of the dressing was 3.5, C. botulinum had apparently grown in the shredded cabbage that was suspected to have been packed in a modified atmosphere. A survey subsequently revealed that 12 of 88 cabbages obtained from supermarkets contained C. botulinum spores, and that botulinum toxin can be formed in shredded cabbage when the cabbage is packaged under an atmosphere containing reduced oxygen and stored at 22-25°C (71.7-77°F) for 4-6 d. The appearance and color of the stored cabbage was acceptable when toxin was present. Other vegetables that appear to support growth and toxin production of C. botulinum before spoilage is detected are cubed butternut squash and sliced onions (Table G/S4).
The high rate of respiration of mushrooms can create an anaerobic environment within film-wrapped packages, thus favoring botulinal toxin production. Botulinal toxin was produced in polyvinyl chloride film-packaged mushrooms held at 20°C (68°F) for 3-4 d, and the toxic mushrooms appeared to be edible (Sugiyama and Yang 1975). Although placing holes in film reduces the shelf life of mushrooms, this practice is encouraged so as to prevent C. botulinum growth. Proteolytic strains of C. botulinum grew and produced toxin in vacuum-packaged Enoki mushrooms held at 15-27°C (59-80.6°F), but the mushrooms were visibly spoiled at the time toxin was detected (Malizio and Johnson 1991).
Bacillus cereus has been associated with one outbreak related to the consumption of mixed seed sprouts (Table O4). The organism was subsequently shown to be present at relatively high levels in a variety of seeds sold for sprouting (Table I2). Clostridium perfringens was associated with one outbreak epidemiologically linked to the consumption of salad. Illness caused by this organism is usually associated with gravies and meat dishes. Large numbers of the organism are required to cause illness and anaerobic conditions and a nutrient-rich environment are essential for growth of the organism. It is not clear how salad (presumably lettuce salad) would provide these conditions.
3.5. Pathogens of greatest concern - Viruses
Outbreaks caused by hepatitis A virus, calicivirus, and Norwalk-like viruses have been associated with the consumption of produce (Table O1, O6, O7, O8). These outbreaks have been associated with frozen raspberries or frozen strawberries, lettuce, melons, salads, watercress, diced tomatoes, and fresh-cut fruit. A number of these outbreaks were the result of contamination via an infected food handler during final preparation (Table O9). Hepatitis A and Norwalk-like viruses are the most commonly documented viral food contaminants. Viruses can be excreted in large numbers by infected individuals and have been isolated from sewage and untreated waste-water used for crop irrigation. Although viruses cannot grow in or on foods, their presence on fresh produce, which may serve as vehicles for infection, is of concern. Of 14 reports of viral gastroenteritis outbreaks cited by Hedberg and Osterholm (1993), a food handler who was ill before or while handling the implicated food was identified as the source of infection in eight outbreaks. Salads were the implicated vehicle in five outbreaks (36%), and cold food items or ice were implicated in all but one outbreak.
The survival of viruses on vegetables has been studied. Several enteroviruses (poliomyelitis, enteroviruses, hepatitis A, rotavirus, and Coxsackie viruses) can survive in a variety of raw vegetables for periods exceeding the normal shelf life of salad vegetables (Table G/S8). Survival appears to be dependent upon the pH, moisture content, and temperature. These observations indicate that salad vegetables can serve as vehicles for the transmission of viral pathogens to humans.
3.6. Pathogens of greatest concern - Protozoan parasites
Reliable and sensitive detection methods for parasites in raw produce are lacking and therefore, incidence studies are not available with the exception of one Costa Rican survey. In Costa Rica, Monge and Chinchilla (1996) surveyed a total of 640 samples from eight different vegetables for the presence of Cryptosporidium oocysts, fecal coliforms, and generic E. coli. Escharichia coli was found at populations of 101 (tomato) to 105/106 MPN/g (cilantro leaves/cilantro roots). Cryptosporidium oocysts were found in at least one of 80 samples of each vegetable except cabbage. Highest isolation rates were seen for cilantro leaves (5 of 80 samples positive) and cilantro roots (7 of 80 samples positive). Highest contamination rates were observed in the rainy season and the probable contamination route was thought to be the use of contaminated irrigation water. No correlation was observed between the presence of Cryptosoridium oocysts and populations of fecal coliforms or generic E. coli.
3.6.1. Cryptosporidium parvum
Cryptosporidium parvum is an obligate intracellular parasite. It is currently thought that the form infecting humans is the same species that causes disease in young calves. The forms that infect avian hosts and those that infect mice are not thought capable of infecting humans. Cryptosporidium sp. infects many herd animals (cows, goats, and sheep among domesticated animals, and deer and elk among wild animals). The infective stage of the organism is the oocyst. The sporocysts are resistant to most chemical disinfectants, but are susceptible to drying and the ultraviolet portion of sunlight.
Intestinal cryptosporidiosis is characterized by severe watery diarrhea that is particularly severe in immune compromised individuals. Healthy adults may be asymptomatic. The infectious dose is less than 10 organisms and, presumably, one organism can initiate an infection. Oocysts are shed in the infected individual's feces. Cryptosporidium sp. could occur, theoretically, on any food touched by a contaminated food handler. The incidence is higher in child day care centers that serve food. Fertilizing salad vegetables with manure is another possible source of human infection. Large outbreaks have been associated with contaminated water supplies suggesting that contaminated irrigation water could be another route of contamination. Produce- and juice-associated outbreaks of cryptosporidiosis have occurred (Table O-5, O-8).
3.6.2. Cyclospora cayetanensis
Cyclospora cayetanensis is a unicellular parasite previously known as cyanobacterium-like or coccidia-like body (CLB). The first known human cases of illness caused by Cyclospora infection (for example, cyclosporiasis) were reported in the medical literature in 1979. Cases have been reported with increased frequency from various countries since the mid 1980s, in part because of the availability of better techniques for detecting the parasite in stool specimens.
Infected persons excrete the oocyst stage of Cyclospora in their feces. When excreted, oocysts are not infectious and may require days to weeks to become infectious (for example, to sporulate). Therefore, transmission of Cyclospora directly from an infected person to someone else is unlikely. However, indirect transmission can occur if an infected person contaminates the environment and oocysts have sufficient time, under appropriate conditions, to become infectious. For example, Cyclospora may be transmitted by ingestion of water or food contaminated with oocysts. Outbreaks linked to contaminated water, as well as outbreaks linked to various types of fresh produce, have been reported in recent years. Raspberries and possibly blackberries imported from Guatamala have been implicated in at least five outbreaks, two involving numerous states and Canadian provinces (Table O2). The route of contamination was not conclusively determined, but was suspected to be related to contaminated water used for irrigation or pesticide application. Berries imported in the spring but not in the fall were associated with illnesses suggesting a seasonality to the illness. In addition, fresh basil and products made from the basil were implicated in an outbreak in 1997 (Table O8). The source of contamination for this outbreak was not determined. How common the various modes of transmission and sources of infection are is not yet known, nor is it known whether animals can be infected and serve as sources of infection for humans. The incubation period between acquisition of infection and onset of symptoms averages 1 week. Cyclospora infects the small intestine and typically causes watery diarrhea, with frequent, sometimes explosive, stools. Other symptoms can include loss of appetite, substantial loss of weight, bloating, increased flatus, stomach cramps, nausea, vomiting, muscle aches, low-grade fever, and fatigue. If untreated, illness may last for a few days to a month or longer, and may follow a remitting-relapsing course. Some infected persons are asymptomatic.
3.6.3. Giardia lamblia
Organisms that appear identical to those that cause human illness have been isolated from domestic animals (dogs and cats) and wild animals (beavers and bears). A related but morphologically distinct organism infects rodents, although rodents may be infected with human isolates in the laboratory. Human giardiasis may involve diarrhea within 1 week of ingestion of the cyst, which is the environmental survival form and infective stage of the organism. Normally, illness lasts for 1 to 2 weeks, but there are cases of chronic infections lasting months to years. Chronic cases, both those with defined immune deficiencies and those without, are difficult to treat. Different individuals show various degrees of symptoms when infected with the same strain, and the symptoms of an individual may vary during the course of the disease.
Ingestion of one or more cysts may cause disease. Giardiasis is most frequently associated with the consumption of contaminated water. Cool moist conditions favor the survival of the organism. Produce-related outbreaks have been linked to lettuce, tomatoes, and onions (Table O7, O8).
- Numerous microorganisms, most of them from enteric environments (for example, Salmonella spp., E. coli O157:H7, C.jejuni) but also from other sources (for example, C. botulinum and L. monocytogenes) have been isolated from a variety of fresh fruits and vegetables.
Although isolation rates can be high, they are not consistent. The percentage of samples contaminated ranges from 0 to 50%, depending upon the product and target pathogen. Because of differences in their production systems, surface morphology, or other factors, produce items, such as lettuce, berries, seed sprouts, melons, seem to provide conditions for pathogen survival and/or growth.
The number of foodborne illness outbreaks linked to fresh produce and reported to the United States Centers for Disease Control and Prevention (CDC) has increased in the last years. Some of this increase is due to improved surveillance, but other factors may also come into play, such as increase in consumption, change in consumers' habits, and complex distribution systems.
Foodborne illness resulting from the consumption of any food is dependant upon a several factors. For example, the produce must be contaminated with a pathogen that survives or grows to infective level doses at the time of consumption. Temperature abuse and growth is not always necessary for foodborne illness to occur.
Conditions for survival and/or growth of pathogens on fresh produce necessary for illness are influenced by the type of microorganism, produce item, and environmental conditions in the field and subsequent handling and storage. For example, free moisture resulting from condensation rain or irrigation may promote survival and growth of microbial populations in an otherwise inhospitable environment.
After harvest, pathogens will survive but not grow on the outer surface of most fresh fruits and vegetables, especially if the humidity is high. In some cases, pathogen levels will decline on the outer surface. The rate of decline is dependent upon the produce type, humidity, and temperature, as well as the atmosphere and type of packaging used.
Survival and multiplication of foodborne pathogens on produce is significantly enhanced once the protective epidermal barrier has been broken either by physical damage, such as punctures or bruising, or by degradation by plant pathogens.
Physically damage produce and fresh cut produce can promote the multiplication of pathogens, especially at nonrefrigerated temperatures. At refrigerated temperatures the ability of the microorganisms to multiply is reduced with the exceptions of psychrotrophic pathogens (for example, non-proteolytic C. botulinum, L. monocytogenes, Y. enterocolitica).
Specifications requiring very low microbial counts may, in some cases, compromise produce safety because the population of nonpathogenic bacteria is potentially a barrier that reduces the risk of illness associated with fresh-cut products.
Under some circumstances (for example, pressure differentials) wash water may enter an intact fruit through the stem scar or other opening, promoting pathogen infiltration. Access to nutrients inside the product may induce pathogen multiplication to hazardous levels. Conditions that reduce infiltration of plant pathogens should also prevent infiltration of human pathogens.
- Packaging of the product under modified atmospheres changes the growth rate of pathogens which may become a concern (for example, growth and toxin production by C. botulinum).
5. Research needs
Continue and increase the number of well-designed incidence studies of pathogens in fresh produce. Isolation studies should be designed considering their statistical relevance, consistency (for example, consistent sample collection, treatment, laboratory test methods, and data analysis) and including testing of control samples. Negative results should also be reported.
Increase surveillance and investigation of fresh produce related outbreaks.
Investigate the relative fitness of human pathogens and common epiphytes (microbes that grow and persist on plant surfaces) and the interaction between bacterial pathogens and indigenous microorganisms.
Determine the effects of various environmental factors (for example, ultraviolet irradiation) on the survival and growth of pathogens of concern.
- Investigate the factors affecting produce infiltration of microorganisms and assess the risk of foodborne disease due to infiltration of pathogen inside produce.
Abdul-Raouf UM, Beuchat LR, Ammar MS. 1993. Survival and growth of Escherichia coli O157:H7 on salad vegetables. Appl Environ Microbiol 59(7):1999-2006.
Ackers M, Mahon BE, Leahly E, Goode B, Damrow T, Hayes PS, Bibb WF, Rice DH, Barrett TJ, Hutwagner L and others. 1998. An outbreak, of Escherichia coli O157:H7 infections associated with leaf lettuce consumption. J Infect Dis 177:1588-93.
Al-Hindawi N, Rished R. 1979. Presence and distribution of Salmonella species in some local foods from Baghdad City, Iraq. J Food Prot 42(11):877-80.
Allen AB. 1985. Outbreak of campylobacteriosis in a large educational institution--British Columbia. Can Dis Weekly Rep 2:28-30.
Andrews WH, Wilson CR, Poelma PL, Romero A, Mislivec PB. 1979. Bacteriological survey of sixty health foods. Appl Environ Microbiol 37(3):559-66.
Andrews PH. 1992. Biological control in the phyllosphere. Ann Rev Phytopathol 30:603-35.
[Anonymous|. 1993. Fourth northwest Sizzler outbreak sickens at least nine. Food Chem News 34:45.
Arumugaswami RK, Ali GRR, Abdul-Hamid SNB. 1994. Prevalence of Listeria monocytogenes in foods in Malaysia. Int J Food Microbiol 23:117-21.
Asplund K, Nurmi E. 1991. The growth of salmonellae in tomatoes. Int J Food Microbiol 13(2):177-82.
Austin JW, Dodds KL, Blanchfield B, Farber JM. 1998. Growth and toxin production by Clostridium botulinum on inoculated fresh-cut packaged vegetables. J Food Prot 61(3):324-8.
Aytac SA, Gorris LGM. 1994. Survival of Aeromonas hydrophila and Listeria monocytogenes on fresh vegetables stored under moderate vacuum. World J Microbiol Biotechnol 10:670-2.
Backer HD, Mohle-Boetani JC, Werner SB, Abbott SL, Farrar J, Vugia DJ. 2000. High incidence of extra-intestinal infections in a Salmonella havana outbreak associated with alfalfa sprouts. Pub Health Rep 115:339-45.
Badawy AS, Gerba CP, Kelley LM. 1985. Survival of rotavirus SA-11 on vegetables. Food Microbiol 2:199-205.
Bagdasaryan GA. 1964. Survival of viruses of the enterovirus group (poliomyelitis, echo, coxsackie) in soil and on vegetables. J Hyg Epidemiol Microbiol Immunol 8:497-505.
Bartz JA. 1999. Washing fresh fruits and vegetables: lessons from treatment of tomatoes and potatoes with water. Dairy Food Environ Sanit 19(12):853-64.
Bean NH, Griffin PM. 1990. Foodborne disease outbreaks in the United States, 1973-1987: pathogens, vehicles, and trends. J Food Prot 53(9):804-17.
Beattie GA, Lindow SE. 1995. The secret life of foliar bacterial pathogens on leaves. Ann Rev Phytopathol 33:145-72.
Beattie GA, Lindow SE. 1999. Bacterial colonization of leaves: a spectrum of strategies. Phytopathol 89(5):353-9.
Berrang ME, Brackett RE, Beuchat LR. 1989a. Growth of Listeria monocytogenes on fresh vegetables stored under controlled atmosphere. J Food Prot 52(10):702-5.
Berrang ME, Brackett RE, Beuchat LR. 1989b. Growth of Aeromonas hydrophila on fresh vegetables stored under a controlled atmosphere. Appl Environ Microbiol 55(9):2167-71.
Besser RES, Lett SM, Weber JT, Doyle MP, Barrett TJ, Wells JG, Griffin PM. 1993. An outbreak of diarrhea and hemolytic uremic syndrome from Escherichia coli O157-H7 in fresh-pressed apple cider. J Am Med Assoc 269:2217-20.
Beuchat LR, Brackett RE, Hao DYY, Conner DE. 1986. Growth and thermal inactivation of Listeria monocytogenes in cabbage and cabbage juice. Can J Microbiol 32:791-5.
Beuchat LR, Brackett RE. 1990a. Survival and growth of Listeria monocytogenes on lettuce as influenced by shredding, chlorine treatment, modified atmosphere packaging and temperature. J Food Sci 55(3):755-8, 870.
Beuchat LR, Brackett RE. 1990b. Inhibitory effects of raw carrots on Listeria monocytogenes. Appl Environ Microbiol 56(6):1734-42.
Beuchat LR, Brackett RE. 1991. Behavior of Listeria monocytogenes inoculated into raw tomatoes and processed tomato products. Appl Environ Microbiol 57(5):1367-71.
Beuchat LR, Brackett RE, Doyle MP. 1994. Lethality of carrot juice to Listeria monocytogenes as affected by pH, sodium chloride and temperature. J Food Prot 57(6):470-4.
Beuchat LR, Doyle MP. 1995. Survival and growth of Listeria monocytogenes in foods treated or supplemented with carrot juice. Food Microbiol 12:73-80.
Beuchat LR. 1996a. Listeria monocytogenes: incidence on vegetables. Food Control 7(4/5):223-8.
Beuchat LR. 1996b. Pathogenic microorganisms associated with fresh produce. J Food Prot 59(2):204-16.
Bidawid S, Farber JM, Sattar SA. 2001. Survival of hepatitis A virus on modified atmosphere packaged (MAP) lettuce. Food Microbiol 18(1):95-102.
Birkhead GS, Morse DL, Levine WC, Fudala JK, Kondracki SF, Chang HG, Shayegani M, Novick L, Blake PA. 1993. Typhoid fever at a resort hotel in New York: a large outbreak with an unusual vehicle. J Infect Dis 167:1228-32.
Blakeman JP, editor. 1981. Microbial ecology of the phylloplane. London: Academic Press. 502 p.
Blenden DC, Szatalowicz FT. 1967. Ecological aspects of listeriosis. J Am Vet Med Assoc 151:1761-6.
Blostein J. 1993. An outbreak of Salmonella javiana associated with consumption of watermelon. J Environ Health 56(1):29-31.
Brocklehurst, Zaman-Wong CM, Lund BM. 1987. A note on the microbiology of retail packs of prepared salad vegetables. J Appl Bacteriol 63:409-15.
Butler ME. 2000 April 24. Salmonella outbreak leads to juice recall in Western states. Food Chem News 42(10):19.
Callister SM, Agger WA. 1987. Enumeration and characterization of Aeromonas hydrophilia and Aeromonas caviae isolated from grocery store produce. Appl Environ Microbiol 53(2):249-53.
Carlin F, Nguyen-The C. 1994. Fate of Listeria monocytogenes on four types of minimally processed green salads. Lett Appl Microbiol 18:222-6.
Carlin F, Nguyen-the C, Abreu da Silva A. 1995. Factors affecting the growth of Listeria monocytogenes on minimally processed fresh endive. J Appl Bacteriol 78:636-46.
Carlin F, Nguyen-the C, Da Silva AA, Cochet C. 1996. Effects of carbon dioxide on the fate of Listeria monocytogenes, of aerobic bacteria and on the development of spoilage in minimally processed fresh endive. Int J Food Microbiol 32:159-72.
Castillejo Rodriguez AM, Barco-Alcala E, Garcia-Gimeno RM, Zurera-Cosano G. 2000. Growth modelling of Listeria moncytogenes in packaged fresh green asparagus. Food Microbiol 17:421-7.
Castillo A, Escartin EF. 1994. Survival of Campylobacter jejuni on sliced watermelon and papaya [a research note]. J Food Prot 57(2):166-8.
Castro-Rosas J, Escartin EF. 2000. Survival and growth of Vibrio cholerae O1, Salmonella typhi, and Escherichia coli O157:H7 in alfalfa sprouts. J Food Sci 65(1):162-5.
Catteau M, Krembel C, Wauters G. 1985. Yersinia in raw vegetables. Sci Aliments 5:103-6.
CDC. 1971. Infectious Hepatitis--Tennessee. MMWR 20:357.
CDC. 1975. Salmonella typhimurium outbreak traced to a commercial apple cider--New Jersey. MMWR 24:87.
CDC. 1979. Salmonella oranienburg gastroenteritis associated with consumption of precut watermelons-Illinois. MMWR 28:522-3.
CDC. 1989. Epidemiologic notes and reports common-source outbreak of giardiasis--New Mexico. MMWR 38:405-7.
CDC. 1990. CDC surveillance summaries; March 1, 2000. MMWR 39(SS-1):15-23.
CDC. 1991. Multi-state outbreak of Salmonella poona infections - United States and Canada 1991. MMWR 40:549-52.
CDC. 1994. Foodborne outbreaks of enterotoxigenic Escherichia coli-Rhode Island and New Hampshire, 1993. MMWR 43:81, 7-8.
CDC. 1995. Outbreak of S. hartford among travellers to Orlando, FA, May 1995. Atlanta, GA: CDC.
CDC. 1996a. Foodborne outbreak of diarrheal illness associated with Cryptosporidium parvum--Minnesota, 1995. MMWR 45(36):783-5.
CDC. 1996b. Outbreak of Escherichia coli O157:H7 infections associated with drinking unpasteurized commercial apple juice -- British Columbia, California, Colorado, and Washington, October 1996. MMWR 45(44):975.
CDC. 1997a. Hepatitis A associated with consumption of frozen strawberries- Michigan, March 1997. MMWR 46:288-9.
CDC. 1997b. Outbreak of cyclosporiasis-Northern Virginia-Washington DC-Baltimore, Maryland metropolitan area, 1997. MMWR 46(30):689-91.
CDC. 1997c. Outbreaks of Escherichia coli 0157:H7 infection and cryptosporidiosis associated with drinking unpasteurized apple cider--Connecticut and New York, October 1996. MMWR 46:4-8.
CDC. 1997d. Outbreaks of Escherichia coli O157:H7 infection associated with eating alfalfa sprouts- Michigan and Virginia, June-July 1997. MMWR 46(32):741-4.
CDC. 1998a. Foodborne outbreak of cryptosporidiosis--Spokane, Washington, 1997. MMWR 47(565-7).
CDC. 1998b. Outbreak of Campylobacter enteritis associated with cross-contamination of food--Oklahoma, 1996. MMWR 47:129-31.
CDC. 1998c. Outbreak of cyclosporiasis--Ontario, Canada, May 1998. MMWR 47:806-9.
CDC. 1999a. Outbreak of Salmonella serotype Muenchen infections associated with unpasteurized orange juice--United States and Canada, July 1999. MMWR 48:582-5.
CDC. 1999b. Outbreaks of Shigella sonnei infection associated with eating fresh parsley-United States and Canada, July-August 1998. MMWR 48:285-9.
CDC. 2000. CDC surveillance summaries; March 17, 2000. MMWR 49(SS-1):1-51.
Cody SH, Glynn K, Farrar JA, Cairns KL, Griffin PM, Kobayashi J, Fyfe M, Hoffman R, King AS, Lewis JH and others. 1999. An outbreak of Escherichia coli 0157:H7 infection from unpasteurized commercial apple juice. An Intern Med 130:202-9.
Cook KA, Dobbs TE, Hlady WG, Wells JG, Barrett TJ, Puhr ND, Lancette GA, Bodager DW, Toth BL, Genese CA and others. 1998. Outbreak of Salmonella serotype Hartford infections associated with unpasteurized orange juice. J Am Med Assoc 280:1504-9.
Cover TL, Aber RC. 1989. Yersinia enterocolitica. New Engl J Med 321:16-24.
[CSPI] Center for Science in the Public Interest. Updated and Revised 2000 Aug. Outbreak alert! Closing the gaps in our federal food-safety net (Appendix A Outbreaks traced to FDA-regulated foods, 1990-2000). Lkd. from: . Accessed 2001 Aug 28.
Cummings K. 1999 Sept 20. Salmonella outbreak linked to raw tomatoes in California. In: 39th Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC): a meeting of the American Society for Microbiology; 1999 Sept 26-29; San Francisco, CA. Herndon (VA): ASM Pr. Session 213. L/M, Paper 2216.
Darbas H, Riviere M, Oberti J. 1985. Yersinia in refrigerated vegetables. Sci Aliments 5:81-4.
Davis H, Taylor JP, Perdue JN, Stelma Jr. GN, Humphreys Jr. JM, Rowntree III R, Greene KD. 1988. A shigellosis outbreak traced to commercially distributed shredded lettuce. Am J Epidemiol 128(6):1312-21.
de Simon M, Tarrago C, Ferrer MD. 1992. Incidence of Listeria monocytogenes in fresh foods in Barcelona [Spain]. Int J Food Microbiol 16:153-6.
Deeks S, Ellis A, Ciebin B, Khakhria R, Naus M, Hockin J. 1998. Salmonella oranienburg, Ontario. Can Comm Dis Rep 24:177-9.
Del Rosario BA, Beuchat LR. 1995. Survival and growth of enterohemorrhagic Escherichia coli O157:H7 in cantaloupe and watermelon. J Food Prot 58(1):105-7.
Dickinson CH. 1986. Adaptations of micro-organisms to climatic conditions affecting aerial plant surfaces. In: Fokkema NJ, van den Heuvel J, editors. Microbiology of the phyllosphere. New York: Cambridge Univ. p 77-100.
Dingman DW. 2000. Growth of Escherichia coli 0157:H7 in bruised apple (Malus domestica) tissue as influenced by cultivar, date of harvest, and source. Appl Environ Microbiol 66:1077-83.
dos Reis Tassinari A, Melo Franco BDG, Landgraf M. 1994. Incidence of Yersinia spp. in food in Sao Paulo, Brazil. Int J Food Microbiol 21(3):263-70.
Doyle MP, Schoeni JL. 1986. Isolation of Campylobacter jejuni from retail mushrooms. Appl Environ Microbiol 51(2):449-50.
Duncan TG, Doull JA, Miller ER, Bancroft H. 1946. Outbreak of typhoid fever with orange juice as the vehicle, illustrating the value of immunization. Am J Public Health 36:34-6.
Einstein AB, Jacobsohn W, Goldman A. 1963. An epidemic of infectious hepatitis in a general hospital: probable transmission by contaminated orange juice. J Am Med Assoc 185:171-4.
Ercolani GL. 1976. Bacteriological quality assessment of fresh marketed lettuce and fennel. Appl Environ Microbiol 31(6):847-52.
Farber JM, Sanders GW, Johnston MA. 1989. A survey of various foods for the presence of Listeria species. J Food Prot 52(7):456-8.
Farber JM, Wang SL, Cai Y, Zhang S. 1998. Changes in populations of Listeria monocytogenes inoculated on packaged fresh-cut vegetables. J Food Prot 61(2):192-5.
Farber JM. 2000 Oct. Qualitative risk assessment unpasteurized fruit juice/cider. Ottawa, Ontario: Health Canada, Food Directorate, Health Products and Food Branch. 27 p. Available from: Jeff_Farber@hc-sc.gc.ca.
[FDA] Food and Drug Administration, Center for Food Safety and Applied Nutrition, Office of Plant and Dairy Foods and Beverages. 2001 Jan 30. FDA survey of imported fresh produce. FY 1999 Field Assignment. . Accessed 2001 Aug 10.
Feng P. Updated 1999 Aug 18. A summary of background information and foodborne illness associated with the consumption of sprouts. Food and Drug Administration, Center for Food Safety and Applied Nutrition.
Fernandez Escartin EF, Castillo Ayala A, Saldana Lozano J. 1989. Survival and growth of Salmonella and Shigella on sliced fresh fruit. J Food Prot 52(7):471-2.
Fisher TL, Golden DA. 1998. Fate of Escherichia coli O157:H7 in ground apples used in cider production. J Food Prot 61(10):1372-4.
Fleming CA, Caron D, Gunn JE, Barry MA. 1998. A foodborne outbreak of Cyclospora cayetanensis at a wedding. Arch Intern Med 158:1121-5.
Francis GA, Thomas C, O'Beirne D. 1999. The microbiological safety of minimally processed vegetables [review article]. Int J Food Sci Technol 34:1-22.
Fredlund H, Back E, Sjoberg L, Tornquist E. 1987. Watermelon as a vehicle of transmission of Shigellosis. Scand J Infect Dis 19:219-21.
Garcia-Gimeno RM, Sanchez-Pozo MD, Amaro-Lopez MA, Zurera-Cosano G. 1996. Behaviour of Aeromonas hydrophila in vegetable salads stored under modified atmosphere at 4 and 15°C. Food Microbiol 13:369-74.
Garcia-Villanova Ruiz B, Cueto Espinar A, Bolanos Carmona MJ. 1987. A comparative study of strains of salmonella isolated from irrigation waters, vegetables and human infections. Epidemiol Infect 98:271-6.
Garcia-Villanova Ruiz B, Galvez Vargas R, Garcia-Villanova R. 1987. Contamination on fresh vegetables during cultivation and marketing. Int J Food Microbiol 4:285-91.
Gaulin CD, Ramsay D, Cardinal P, Halevyn MAD. 1999. Epidemic of gastroenteritis of viral origins associated with eating imported raspberries. Can J Pub Health 90:37-40.
Gayler GE, MacCready RA, Reardon JP, McKernan BF. 1955. An outbreak of Salmonellosis traced to watermelon. Public Health Reports 70(3):311-3.
Golden DA, Rhodehamel EJ, Kautter DA. 1993. Growth of Salmonella spp. in cantaloupe, watermelon, and honeydew melons. J Food Prot 56(3):194-6.
Gras MH, Druet-Michaud C, Cerf O. 1994. La flore bacterienne des feuilles de salade fraiche (Bacterial flora of salad leaves). Sci Aliments 14:173-88.
Griffin PM, Tauxe RV. Updated 2001 June 20. Surveillance for outbreaks of Escherichia coli 0157:H7 infection summary of 1998 data. Center for Disease Control, National Center for Infectious Diseases, Division of Bacterial and Mycotic Diseases (Atlanta, GA). Accessed 2001 Aug 10.
Hall HE, Brown DF, Lewis KH. 1967. Examination of market foods for coliform organisms. Appl Microbiol 15:1062-9.
Harmon SM, Kautter DA, Solomon HM. 1987. Bacillus cereus contamination of seeds and vegetable sprouts grown in a home sprouting kit. J Food Prot 50(1):62-5.
Harvey J, Gilmour A. 1993. Occurrence and characteristics of Listeria in foods produced in Northern Ireland. Int J Food Microbiol 19:193-205.
Hedberg CW, Osterholm MT. 1993. Outbreaks of food-borne and waterborne viral gastroenteritis. Clin Microbiol Rev 6(3):199-210.
Heisick JE, Wagner DE, Nierman ML, Peeler JT. 1989. Listeria spp. found on fresh market produce. Appl Environ Microbiol 55(8):1925-7.
Herwaldt BL, Lew JF, Moe CL, Lewis DC, Humphrey CD, Monroe SS, Pon EW, Glass RI. 1994. Characterization of a variant strain of norwalk virus from a foodborne outbreak of gastroenteriitis on a cruise ship in Hawaii. J Clin Microbiol 32:861-6.
Herwaldt BL, Ackers ML. 1997. An Outbreak in 1996 of cyclosporiasis associated with imported raspberries. New Engl J Med 336(22):1548-56.
Herwaldt BL, Beach MJ. 1999. The return of Cyclospora in 1997: another outbreak of cyclosporiasis in North America associated with imported berries. Ann of Intern Med 130:210-9.
Herwaldt BL. 2000. Cyclospora cayetanensis: a review, focusing on the outbreaks of cyclosporiasis in the 1990s. Clin Infect Dis 31:1040-57.
Hillborn ED, Mermin JH, Mshar PA, Hadler JL, Voetsch A, Wojtkunski C, Swartz M, Mshar R, Lambert-Fair MA, Farrar JA and others. 1999. A multistate outbreak of Escherichia coli 0157:H7 infections associated with consumption of mesclun lettuce. J Am Med Assoc 159:1758-64.
Ho JL, Shands KN, Friedland G, Eckind P, Fraser DW. 1986. An outbreak of type 4b Listeria monocytogenes infection involving patients from eight Boston hospitals. Arch Intern Med 146:520-3.
Hutin YJF, Pool V, Cramer EH, Nainan OV, Weth J, Williams IT, Goldstein ST, Gensheimer KF, Bell BP, Shapiro CN and others. 1999. A multistate, foodborne outbreak of hepatitis A. New Eng J Med 340:595-602.
Jagger J. 1981. Near-UV radiation effects on microorganisms. Photochemistry and Photobiology 34:761-8.
Janisiewicz WJ, Conway WS, Brown MW, Sapers GM, Fratamico P, Buchanan RL. 1999. Fate of Escherichia coli O157:H7 on fresh-cut apple tissue and its potential for transmission by fruit flies. Appl Environ Microbiol 65(1):1-5.
Jaquette CB, Beuchat LR, Mahon BE. 1996. Efficacy of chlorine and heat treatment in killing Salmonella stanley inoculated onto alfalfa seeds and growth and survival of the pathogen during sprouting and storage. Appl Environ Microbiol 62(6):2212-5.
Jerngklinchan J, Saitanu K. 1993. The occurrence of Salmonellae in bean sprouts in Thailand. Southeast Asean J Trop Med Public Health 24(1):114-8.
Kallander KD, Hitchins AD, Lancette GA, Schmieg JA, Garcia GR, Solomon HM, Sofos JN. 1991. Fate of Listeria monocytogenes in shredded cabbage stored at 5 and 25 degrees C under a modified atmosphere. J Food Prot 54(4):302-4.
Kapperud G, Rorvik LM, Hasseltvedt V, Hoiby EA, Iversen BG, Staveland K, Johnsen G, Leitao J, Herikstad H, Andersson Y and others. 1995. Outbreak of Shigella sonnei infection traced to imported iceberg lettuce. J Clin Microbiol 33(3):609-14.
Konowalchuk J, Speirs JI. 1974. Recovery of coxsackievirus B5 from stored lettuce. J Milk Food Technol 37:132-4.
Konowalchuk J, Speirs JI. 1975. Survival of enteric viruses on fresh vegetables. J Milk Food Technol 38:469-72.
Koumans EHA, Katz DJ, Malecki JM, Kumar S, Wahlquist SP, Arrowood MJ, Hightower AW, Herwaldt BL. 1998. An outbreak of cyclosporiasis in Florida in 1995: a harbinger of multistate outbreaks in 1996 and 1997. J Trop Med Hyg 59:235-42.
Lang MM, Ingham BH, Ingham SC. 2000. Efficacy of novel organic acid and hypochlorite treatments for eliminating Escherichia coli 0157:H7 from alfalfa seeds prior to sprouting. Int J Food Microbiol 58:73-82.
Larson AE, Johnson EA, Barmore CR, Hughes MD. 1997. Evaluation of the botulism hazard from vegetables in modified atmosphere packaging. J Food Prot 60(10):1208-14.
Li Y, Brackett RE, Chen J, Beuchat LR. 2001. Survival and growth of Escherichia coli 0157:H7 inoculated onto cut lettuce before or after heating in chlorinated water, followed by storage at 5°C or 15°C. J Food Prot 64(3):305-9.
Liao C-H, Sapers GM. 2000. Attachment and growth of Salmonella chester on apple fruit and in vivo response of attached bacteria to sanitizer treatments. J Food Prot 63(7):876-83.
Lilly T, Solomon HM, Rhodehamel EJ. 1996. Incidence of Clostridium botulinum in vegetables packaged under vacuum or modified atmosphere. J Food Prot 59(1):59-61.
Lin C-M, Fernando SY, Wei CI. 1996. Occurrence of Listeria monocytogenes, Salmonella spp., Escherichia coli and E. coli O157:H7 in vegetable salads. Food Control 7:135-40.
Lin C-M, Kim J, Du W-X, Wei C-I. 2000. Bactericidal activity of isothiocyanate against pathogens on fresh produce. J Food Prot 63(1):25-30.
Little C, Roberts D, Youngs E, de Louvois J. 1999. Microbiological quality of retail imported unprepared whole lettuces: a PHLS Food Working Group Study. J Food Prot 62(4):325-8.
Lowry PW, Levine R, Stroup DF, Gunn RA, Wilder MH, Konigsberg C. 1989. Hepatitis A outbreak on a floating restaurant in Florida, 1986. Am J Epidemiol 129:155-64.
Lund BM, Snowdon AL. 2000. Fresh and processed fruits, Chapter 27. In: Lund BM, Baird-Parker TC, Gould GW, editors. The microbiological safety and quality of food, Volume I. Gaithersburg (MD): Aspen. p 738-58.
MacGowan AP, Bowker K, McLauchlin J, Bennett PM, Reeves DS. 1994. The occurrence and seasonal changes in the isolation of Listeria spp. in shop bought food stuffs, human faeces, sewage and soil from urban sources. Int J Food Microbiol 21:325-34.
Madden JM. 1992. Microbial pathogens in fresh produce-the regulatory perspective. J Food Prot 55(10):821-3.
Mahon BE, Ponka A, Hall WN, Komatsu K, Dietrich SE, Siitonen A, Cage G, Lambert-Fair MA, Hayes PS, Bean NH and others. 1997. An international outbreak of Salmonella infections caused by alfalfa sprouts grown from contaminated seeds. J Infect Dis 175:876-82.
Malizio CJ, Johnson EA. 1991. Evaluation of the botulism hazard from vacuum-packaged enoki mushrooms [Flammulina velutipes]. J Food Prot 54(1):20-1.
Marchetti R, Casadei MA, Guerzoni ME. 1992. Microbial population dynamics in ready-to-use vegetable salads. Ital J Food Sci 2:97-108.
Martin DL, Gustafson TL, Pelosi JW, Suarez L, Pierce GV. 1986. Contaminated produce-a common source for two outbreaks of Shigella gastroenteritis. Am J Epidemiol 124(2):299-305.
Merson MH, Morris GK, Sack DA, Wells JE, Feeley JC, Sack RB, Creech WB, Kapikian AZ, Gangarosa EJ. 1976. Travelers' diarrhea in Mexico. N Engl J Med 294:1299-305.
Millard PS, Gensheimer KF, Addiss DG, Sosin DM, Beckett GA, Houck-Jankoski A, Hudson A. 1994. An outbreak of cryptosporidiosis from fresh-pressed apple cider. JAMA 272(20):1592-6.
Mohle-Boetani JC, Reporter R, Werner SB, Abbott S, Farrar J, Waterman SH, Vugia DJ. 1999. An outbreak of Salmonella serogroup Saphra due to cantaloupes from Mexico. J Infect Dis 180:1361-4.
Monge R, Chinchilla M. 1996. Presence of Cryptosporidium oocysts in fresh vegetables. J Food Prot 59(2):202-3.
Morse DL, Pickard LK, Guzewich JJ, Devine BD, Shayegani M. 1990. Garlic-in-oil associated botulism: episode leads to product modification. Am J Pub Health 80(11):1372-3.
[NACMCF] National Advisory Committee on Microbiological Criteria for Foods. 1999. Microbiological safety evaluations and recommendations on fresh produce. Food Control 10:117-43.
Nguyen-the C, Lund BM. 1991. The lethal effect of carrot on Listeria species. J Appl Bacteriol 70:479-88.
Nguyen-the C, Lund BM. 1992. An investigation of the antibacterial effect of carrot on Listeria monocytogenes. J Appl Bacteriol 73:23-30.
Nguyen-the C, Carlin F. 2000. Fresh and processed vegetables. In: Lund BM, Baird-Parker TC, Gould GW, editors. The microbiological safety and quality of food. Gaithersburg (MD): Aspen. p 620-84.
Niu MT, Polish LB, Robertson BH, Khanna BK, Woodruff BA, Shapiro CN, Miller MA, Smith JD, Gedrose JK, Alter MJ and others. 1992. Multistate outbreak of hepatitis A associated with frozen strawberries. J Inf Dis 166:518-24.
Notermans S, Dufrenne J, Gerrits JPG. 1989. Natural occurrence of Clostridium botulinum on fresh mushrooms (Agaricus bisporus). J Food Prot 52(10):733-6.
O'Brien RD, Lindow SE. 1988. Effect of plant species and environmental conditions on epiphytic population sizes of Pseudomonas syringae and other bacteria. Phytopathol 79:619-27.
Odumeru JA, Mitchell SJ, Alves DM, Lynch JA, Yee AJ, Wang SL, Styliadis S, Farber JM. 1997. Assessment of the microbiological quality of ready-to-use vegetables for health-care food services. J Food Prot 60(8):954-60.
O'Mahoney M, Cowden J, Smyth B, Lynch D, Hall M, Rowe B, Teare EL, Tettmar RE, Rampling AM, Coles M and others. 1990. An outbreak of Salmonella saint-paul infection associated with beansprouts. Epidemiol Infect 104:229-35.
Pao S, Brown GE, Schneider KR. 1998. Challenge studies with selected pathogenic bacteria on freshly peeled hamlin orange. J Food Sci 63(2):359-62.
Paquet PE. 1923. Epidemie de fievre typhoide: Determinee par la consommation de petit cidre. Revue d'Hygiene 45:165-9.
Parish ME. 1997. Public health and nonpasteurized fruit juices. Crit Rev Microbiol 23(2):109-19.
Parish ME. 1998. Coliforms, Escherichia coli and Salmonella serovars associated with a citrus-processing facility implicated in a salmonellosis outbreak. J Food Prot 61(3):280-4.
Park CE, Sanders GW. 1992. Occurrence of thermotolerant campylobacters in fresh vegetables sold at farmers' outdoor markets and supermarkets. Can J Microbiol 38(4):313-6.
Petran RL, Sperber WH, Davis AR. 1995. Clostridium botulinum toxin formation in romaine lettuce and shredded cabbage: effect of storage and packaging conditions. J Food Prot 58:624-7.
Ponka A, Andersson Y, Siitonen A, de Jong B, Johhola M, Halkala O, Kuhmonan A, Pakkala P. 1995. Salmonella in alfalfa sprouts. Lancet 345:462-3.
Portnoy BL, Goepfert JM, Harmon SM. 1976. An outbreak of Bacillus cereus food poisoning resulting from contaminated vegetable sprouts. Am J Epidemiol 103(6):589-94.
Preston M, Davidson R, Harris S, Thususka J, Goldman C, Green K, Low D, Proctor P, Johnson W, Khakhria R. 1997. Hospital outbreak of Escherichia coli 0157:H7 associated in a rare phage type--Ontario. Can Comm Dis Rep 23:33-7.
Prokopowich D, Blank G. 1991. Microbiological evaluation of vegetable sprouts and seeds. J Food Prot 54(7):560-2.
Rafii F, Lunsford P. 1997. Survival and detection of Shigella flexneri in vegetables and commercially prepared salads. J AOAC Int 80(6):1191-7.
Ramsay CN, Upton PA. 1989 Jan 7. Hepatitis A and frozen raspberries. Lancet 1(8628):43-4.
Reid TMS, Robinson HG. 1987. Frozen raspberries and hepatitis A. Epidem Inf 98:109-12.
Rosenblum LS, Mirkin IR, Allen DT, Safford S, Hadler SC. 1990. A multifocal outbreak of hepatitis A traced to commercially distributed lettuce. AJPH 80(9):1075-9.
Rude RA, Jackson GJ, Bier JW, Sawyer TK, Risty NG. 1984. Survey of fresh vegetables for nematodes, amoebae, and Salmonella. J AOAC Int 67:613-5.
Saddik MF, El-Sherbeeny MR, Bryan FL. 1985. Microbiological profiles of Egyptian raw vegetables and salads. J Food Prot 48(10):883-6.
Sado PN, Jinneman KC, Husby GJ, Sorg SM, Omiecinski CJ. 1998. Identification of Listeria monocytogenes from unpasteurized apple juice using rapid test kits. J Food Prot 61(9):1199-202.
Satchell FB, Stephenson P, Andrews WH, Estela L, Allen G. 1990. The survival of Shigella sonnei in shredded cabbage. J Food Prot 53(7):558-62.
Schelch WF, Lavigne PM, Bortolussi RA, Allen AC, Haldane EV, Wort AJ, Hightower AW, Johnson SE, King SH, Nicholls ES and others. 1983. Epidemic listeriosis--evidence for transmission by food. New Engl J Med 308:203-6.
Singh BR, Kulshereshtha SB, Kapoor KN. 1995. An orange juice borne diarrhoeal outbreak due to enterotoxigenic Escherichia coli. J Food Sci Tech 32:504-6.
Sizmur K, Walker CW. 1988. Listeria in prepacked salads. Lancet:1167.
Solomon HM, Kautter DA. 1988. Outgrowth and toxin production by Clostridium botulinum in bottled chopped garlic. J Food Prot 51(11):862-5.
Solomon HM, Kautter DA, Lilly T, Rhodehamel EJ. 1990. Outgrowth of Clostridium botulimun in shredded cabbage at room temperature under modified atmosphere. J Food Prot 53(10):831-3.
Splittstoesser DF, Queale DT, Andaloro BW. 1983. The microbiology of vegetable sprouts during commercial production. J Food Safety 5:79-86.
Steele BT, Murphy N, Arbus GS, Rance CP. 1982. An outbreak of hemolytic uremic syndrome associated with ingestion of fresh apple juice. J Pediatrics 101(6):963-5.
Steinbruegge EG, Maxcy RB, Liewen MB. 1988. Fate of Listeria monocytogenes on ready to serve lettuce. J Food Prot 51(8):596-9.
Styliadis S. 1993 Oct 22. Clostridium perfringens outbreak in Peterborough County [Public Health Epidemiol Rep]. Toronto (Ontario): Public Health Branch. Available from: Public Health Branch, Ministry of Health and Long-Term Care; 5700 Yonge St., 8th Floor, Toronto, Ontario, M2M 4K5 Canada.
Sugiyama H, Yang KH. 1975. Growth potential of Clostridium botulinum in fresh mushrooms packaged in semipermeable plastic film. Appl Microbiol 30:964-9.
Sundin GW, Kidambi SP, Ullrich M, Bender CL. 1996. Resistance to ultraviolet light in Pseudomonas syringae: sequence and functional analysis of the plasmid-encoded rulAB genes. Gene 177:77-81.
Sundin GW, Jacobs JL. 1999. Ultraviolet radiation (UVR) sensitivity analysis and UVR survival strategies of a bacterial community from the phyllosphere of field-grown peanut (Arachis hypogeae L.). Microb Ecol 38:27-38.
Swerdlow DL, Mintz ED, Rodriguez M, Tejada E, Ocampo C, Espejo L, Greene KD, Saldana W, Seminario L, Tauxe RV and others. 1992. Waterborne transmission of epidemic cholera in Trujillo, Peru; lessons for a continent at risk. Lancet 340(4):28.
Szabo EA, Scurrah KJ, Burrows JM. 2000. Survey for Psychrotrophic bacterial pathogens in minimally processed lettuce. Lett Appl Microbiol 30(6):456-60.
Tabershaw IR, Schmelzer LL, Bruyn HB. 1967. Gastroenteritis from an orange juice preparation. Arch Environ Health 15:72-7.
Tamblyn S, deGrosbois J, Taylor D, Stratton J. 1999. An outbreak of Escherichia coli 0157:H7 infection associated with unpasteurized non-commercial, custom-pressed apple cider--Ontario, 1998. Can Commun Dis Rep 25:113-7.
Tamminga SK, Beumer RR, Kampelmacher EH. 1978. The hygenic quality of vegetables grown in or imported into the Netherlands: a tentative study. J Hyg Camb 80:143-54.
Taormina PJ, Beuchat LR. 1999a. Behavior of enterohemorrhagic Escherichia coli O157:H7 on alfalfa sprouts during the sprouting process as influenced by treatments with various chemicals. J Food Prot 62(8):850-6.
Taormina PJ, Beuchat LR. 1999b. Comparison of chemical treatments to eliminate enterohemorrhagic Escherichia coli O157:H7 on alfalfa seeds. J Food Prot 62(4):318-24.
Taormina PJ, Beuchat LM, Slutsker LM. 1999. Infections associated with eating seed sprouts: an international concern. Emerg Infect Dis 62: 626-34.
Tauxe R, Kruse H, Hedberg C, Potter M, Madden J, Wachsmuth K. 1997. Microbial hazards and emerging issues associated with produce: a preliminary report to the National Advisory Committee on Microbiological Criteria for Foods. J Food Prot 60(11):1400-8.
Tauxe RV. 1997. Emerging foodborne diseases: an evolving public health challenge. Dairy, Food Environ Sanit 17(12):788-95.
Uljas HE, Ingham SC. 1998. Survival of Escherichia coli 0157:H7 in synthetic gastric fluid after cold and acid habituation in apple juice or trypticase soy broth acidified with hydrochloric acid or organic acids. J Food Prot 61(8):939-47.
Wadstrom T, Ljungh A. 1991. Aeromonas and Plesiomonas as food-and waterborne pathogens. Int J Food Microbiol 12(4):303-11.
Webb RB. 1976. Lethal and mutagenic effects of near-ultraviolet radiation. In: Smith KC, editor. Photochemical and Photobiological Reviews. New York: Plenum Pr. p 169-261.
Wei CI, Huang TS, Kim JM, Lin WF, Tamplin ML, Bartz JA. 1995. Growth and survival of Salmonella montevideo on tomatoes and disinfection with chlorinated water. J Food Prot 58(8):829-36.
Weissinger WR, Chantarapanont W, Beuchat LR. 2000. Survival and growth of Salmonella Baildon in shredded lettuce and diced tomatoes, and effectiveness of chlorinated water as a sanitizer. Int J Food Microbiol 62:123-31.
Weissinger WR, McWatters KH, Beuchat LR. 2001. Evaluation of volatile chemical treatments for lethality to Salmonella on alfalfa seeds and sprouts. J Food Prot 64.
Wells JM, Butterfield JE. 1997. Salmonella contamination associated with bacterial soft rot of fresh fruits and vegetables in the marketplace. Plant Dis 81(8):867-72.
White KE. 1986. A foodborne outbreak of Norwalk virus gastroenteritis: evidence for post-recovery transmission. Acute Dis Epidemiol (Field Services Sect) Minnesota Dept Health 124:120-6.
WHO. 1996a. Enterohaemorrhagic Escherichia coli infection. Weekly Epidemiol Rec 30:229-30.
WHO. 1996b. Enterohaemorrhagic Escherichia coli infection. Weekly Epidemiol Rec 35:267-8.
Wong H-C, Chao W-L, Lee S-J. 1990. Incidence and characterization of Listeria monocytogenes in foods available in Taiwan. Appl Environ Microbiol 56(10):3101-4.
Wu FM, Doyle MP, Beuchat LR, Wells JG, Mintz ED, Swaminathan B. 2000. Fate of Shigella sonnei on parsley and methods of disinfection. J Food Prot 63(5):568-72.
Zhao T, Doyle MP, Besser RE. 1993. Fate of enterohemorrhagic Escherichia coli O157:H7 in apple cider with and without preservatives. Appl Environ Microbiol 59(8):2526-30.
Zhuang R-Y, Beuchat LR, Angulo FJ. 1995. Fate of Salmonella montevideo on and in raw tomatoes as affected by temperature and treatment with chlorine. Appl Environ Microbiol 61(6):2127-31.