Authors: George J. Jackson, Joseph M. Madden, Walter E. Hill, and Karl C. Klontz
To investigate a food that has been implicated as the causative vehicle in an outbreak of illness, the microbiologist should make certain observations and perform certain tests as a matter of course; further analysis depends on the circumstances of the particular case. It is always crucial to note the general condition of the food sample, such as its consistency, color, and odor. As much information as possible should be obtained about its pre- and post-collection history (see Chapter l). Microscopic examination and Gram staining must be carried out, as described in Chapter 2.
To decide what treatments, enrichments, or other tests are needed, the microbiologist should evaluate the data in relation to two types of information: l) the causes epidemiologically associated with the type and condition of the implicated food, and 2) the clinical signs and symptoms observed in afflicted individuals. If possible, clinical microbial isolates (usually from stool specimens) and blood serum samples for serological and biochemical testing should be obtained from patients by way of their physicians.
Table l lists the major microbial or chemical agents of foodborne disease and their commonly associated food sources. Recently reported causative agents of foodborne outbreaks, cases, and deaths are given in Table 2. Clinical symptoms most often associated with specific microbial or chemical agents and their duration are listed in Table 3. Analysts should use these tables as an aid in deciding the most probable, less probable, and least likely associations. The tables should not be used to assume a single cause or to eliminate possibilities entirely.
The information in Tables 1-3 concerns mostly those infections designated as "reportable" in the United States by the centers for Disease Control and Prevention (CDC). This agency, which is the principal source of epidemiologic data on reported foodborne disease outbreaks in the United States, periodically publishes summary surveillance reports of foodborne diseases in the Morbidity and Mortality Weekly Report series.
Most reports of foodborne illness are submitted to CDC by state health departments. CDC defines a foodborne disease outbreak as an incident in which at least two (or more) persons experience a similar illness after ingestion of a common food, and epidemiologic analysis implicates the food as the source of the illness. A few exceptions exist; for example, one case of botulism or chemical poisoning constitutes an outbreak. Although CDC's foodborne disease surveillance system has limitations (i.e., except for illnesses linked to chemicals or toxins, sporadic cases of foodborne illness are not reported), the system does provide helpful epidemiologic insights. The etiologic agent was confirmed in 909 (38%) of the 2397 outbreaks of foodborne disease reported to CDC from 1983 through 1987.
With new pathogens there is an inevitable lag before methods are installed and reporting by clinical and food laboratories becomes routine. Changes in food production or processing may make a food the vehicle or growth medium for microorganisms not previously associated with that product. For example, new varieties of tomatoes that are less acidic than the traditional types might support the growth and toxin production of Clostridium botulinum; freezing procedures improved to preserve taste may also preserve microorganisms that are killed in blast freezing. The food microbiologist should be aware that the clinical symptoms and diagnosis of the patient's illness, available when analysis of the food sample must begin, may be preliminary or incomplete. To proceed from the generalities given in the tables to an analytical course of action, the microbiologist must use reason, imagination, and caution.
The authors thank the following FDA microbiologists for their contributions to the tables: Wallace H. Andrews, Reginald W. Bennett, Jeffrey W. Bier, Elisa L. Elliot, Peter Feng, David Golden, Vera Gouvea, Anthony D. Hitchins, E. Jeffery Rhodehamel, and Tony T. Tran.
For more detailed information and instructions on the step-by-step procedures used in investigating foodborne illness, see the Compendium of Methods for the Microbiological Examination of Foods, published by the American Public Health Association of Washington, DC, USA.
Table 1. Number of food-implicated outbreaks in the USA reported to CDC from 1983 to l987, causative agents, and total and confirmed percentages
|Agent||FOOD SOURCE||Total||Total (%)||Con- firmed (%)|
|Beef & pork||Poultry||Other meats||Seafood||Milk, eggs, cheese||Other dairy||Baked goods||Fruits & vegs||Salads||Other||Un-known|
|Streptococcus, Group A||0||0||0||0||0||0||0||0||2||2||3||7||0.3||0.8|
Table 2. Number and percent of confirmed foodborne disease outbreaks cases, and deaths in the USA reported to CDC from 1983 through 1987, listed by etiologic agent
|Streptococcus, Group A||7||0.8||1,001||1.8||0||0.0|
Table 3. Onset, duration, and symptoms of foodborne illnesses(a1)
|Onset and duration of illness||Predominant symptoms||Associated organism or toxin|
|Upper gastrointestinal tract symptoms (nausea, vomiting) occur first or predominate||Less than 1 h||Nausea, vomiting, unusual taste,burning of mouth.||Metallic chemicals(a)|
|1-2 h||Nausea, vomiting, cyanosis, headache, dizziness, dyspnea, trembling, weakness, loss of consciousness.||Nitrites;(b)Paragonimus sp.|
|Onset 1-6 h, mean 2-4 h, duration 1-2 days||Nausea, vomiting, retching, diarrhea, abdominal pain, prostration.||
Staphylococcus aureus and its enterotoxins;
|8-16 h (1-4 h rarely)||Vomiting, abdominal cramps,diarrhea, nausea.||Bacillus cereus|
|6-24 h||Nausea, vomiting, diarrhea, thirst, dilation of pupils, collapse, coma.||
Amanita species mushrooms;(c)
|Sore throat and respiratory symptoms occur||12-72 h||Sore throat, fever, nausea, vomiting, rhinorrhea, sometimes a rash.||
(Lancefield Group A)
|2-5 days||Inflamed throat and nose,spreading grayish exudate,fever, chills, sore throat,malaise, difficulty in swallowing,edema of cervical lymph node.||Corynebacterium diphtheriae|
|Lower gastrointestinal tract symptoms (abdominal cramps, diarrhea) occur first or predominate||2-36 h, mean 6-12 h||Abdominal cramps, diarrhea, putrefactive diarrhea associated with C. perfringens, sometimes nausea and vomiting.||
|4-120 h, mean 18-36 h, duration 1-7 days||Abdominal cramps, diarrhea, vomiting, fever, chills, malaise, nausea, headache possible.Sometimes bloody or mucoid diarrhea, cutaneous lesions and hypotension associated with V. vulnificus; V. cholerae Ol may cause dehydration, shock; Yersinia enterocoliticia mimics flu and acute appendicitis.||Salmonella species
(including S. arizonae),
enteropathogenic Escherichia coli,
Pseudomonas aeruginosa (?),
Campylobacter jejuni (coli),
V. cholerae (O1 and non-O1),
|1-5 days||Diarrhea, fever, vomiting, abdominal pain, respiratory symptoms; often asymptomatic.||Enteroviruses, rotavirus, enteric adenovirus, Norwalk-like viruses; anisakid nematodes, Nanophyetus salmincola; Cryptosporidium parvum|
|1-6 weeks||Mucoid diarrhea (fatty stools), abdominal pain, weight loss.||Giardia lamblia
|1 to several weeks, mean 3-4 weeks||Abdominal pain, diarrhea, constipation, headache, drowsiness, ulcers, variable; often asymptomatic.||Entamoeba histolytica
|3-6 months||Nervousness, insomnia, hunger pains, anorexia, weight loss, abdominal pain, sometimes gastroenteritis.||Taenia saginata, T. solium|
|Neurological symptoms (visual disturbances, vertigo, tingling, paralysis) occur||Less than 1 h||Tingling and numbness, giddiness,staggering, drowsiness, tightness of throat, incoherent speech, respiratory paralysis.||Shellfish toxin(d)|
|Gastroenteritis, nervousness,blurred vision, chest pain,cyanosis, twitching, convulsions.||Organic phosphate(e)|
|Excessive salivation, perspiration, gastroenteritis, irregular pulse,pupils constricted, asthmatic breathing.||Muscaria-type mushrooms(f)|
|Tingling and numbness, dizziness, pallor, gastroenteritis, hemorrhage, and desquamation of skin, fixed eyes, loss of reflexes, twitching, paralysis.||Tetraodon toxin(g)|
|1-6 h||Tingling and numbness, gastroenteritis, dizziness, dry mouth, muscular aches, dilated eyes, blurred vision, paralysis.||Ciguatera toxin(h)|
|Nausea, vomiting, tingling, dizziness, weakness, anorexia,weight loss, confusion.||Chlorinated hydrocarbons(i)|
|2 h to 7 days,
usually 12-36 h
|Vertigo, double or blurred vision,loss of reflex to light, difficulty in swallowing, speaklng, and breathing, dry mouth, weakness, respiratory paralysis, death.||Clostridium botulinum and its neurotoxins|
|More than 72 h||Numbness, weakness of legs, spastic paralysis, impairment of vision, blindness, coma.||Organic mercury(j)|
|Gastroenteritis, leg pain, ungainly high-stepping gait, foot and wrist drop.||Triorthocresyl phosphate(k)|
|Allergic symptoms (facial flushing, itching) occur||Less than 1 h||Headache, dizziness, nausea, vomiting, peppery taste, burning of throat, facial swelling and flushing, stomach pain, itching of skin.||Histamine(1)|
|Numbness around mouth, tingling sensation, flushing, dizziness, headache, nausea, vomiting.||Monosodium glutamate (m)|
|Flushing, sensation of warmth,itching, abdominal pain, puffing of face and knees.||Nicotinic acid(n)|
|1-7 days||Coughing, asthma.||Ascaris lumbricoides|
|General infection symptoms (fever, chills, malaise, prostration, aches, swollen lymph nodes) occur||4-28 days, mean 9 days||Gastroenteritis, fever, edema about eyes, perspiration, muscular pain, chills, prostration, labored breathing.||Trichinella spiralis
|7-28 days, mean 14 days
|Malaise, headache, fever, cough, nausea, vomiting, constipation, abdominal pain, chills, rose spots on abdomen, bloody stools||Salmonella typhi
|10-13 days||Fever, headache, myalgia, rash.||Toxoplasma gondii|
|10-50 days, mean 25-30 days||Fever, malaise, lassitude, anorexia, nausea, abdominal pain, jaundice.||Etiological agent not yet isolated--probably viral (especially Hepatitis A and E viruses)|
|Varying periods (depends on specific illness)||Fever, chills, head- or joint ache, prostration, malaise, swollen lymph nodes, and other specific symptoms of disease in question.||Bacillus anthracis,
B. suis, Coxiella burnetii,
b Consider nitrites, test for decoloration of blood.
c Consider Amanita species mushroom poisning. Identify mushrooms species eaten; test urine and blood for evidence of renal damage (SGOT, SGPT enzyme tests).
d Consider shellfish poisoning.
e Consider organic phosphate insecticide poisoning.
f Consider Muscaria species of mushrooms.
g Consider tetraodon (puffer) fish poisoning.
h Consider ciguatera fish poisoning.
i Consider chlorinated hydrocarbon insecticides.
j Consider organic mercury poisoning.
k Consider triorthocresyl phosphate.
l Consider scombroid poisoning. Examine foods for Proteus species or other organisms capable of decarboxylating histidine into histamine, and for histamine.
m Consider Chinese restaurant syndrome caused by monosodium glutamate, a flavor intensifier.
n Consider nicotinic acid.
(a1) Developed from Compendium of Methods for the Microbiological Examination of Foods (1984), pp. 454-457, American Public Health Association, Washington, DC, with permission of the publisher.
Hypertext Source: Bacteriological Analytical Manual, Edition 8, Revision A, 1998. Chapter 25.