SUBCHAPTER 8.3 - INVESTIGATION OF FOODBORNE OUTBREAKS
- 8.3.1 - FOODBORNE OUTBREAKS
- 220.127.116.11 - Outbreaks on Foreign Flag Vessels
- 18.104.22.168 - Outbreaks Involving Interstate Conveyances
- 22.214.171.124 - Cooperation with Other Agencies
- 126.96.36.199 - Farm Investigations
- 8.3.4 - EPIDEMIOLOGICAL ASSOCIATIONS
- 188.8.131.52 - Outbreak Determination
- 184.108.40.206 - Assistance
- 220.127.116.11 - Additional Case History Interviews
- 18.104.22.168 - Establishment Investigation
- 22.214.171.124 - Food Handlers Interviews
- 126.96.36.199 - Possible Contamination Source
- 188.8.131.52 - Pathogen Growth Factors
The Coordinated Outbreak Response and Evaluation (CORE) Network coordinates FDA’s efforts to prevent, detect, investigate, respond to, evaluate and apply lessons learned from foodborne outbreaks and public health incidents. Along with ORA and others in FDA, CORE directs the strategy and manages the implementation of outbreak response activities and evaluates environmental, epidemiologic, and laboratory data to inform assignments and direction of outbreak investigations related to foods, cosmetics, and dietary supplements.
If you become aware of a foodborne outbreak, contact the appropriate Emergency Response Coordinator in your District and/or Regional Office immediately who will then contact the CORE Signals Team at CORESignalsTeam@fda.hhs.gov.
If a suspect outbreak involving a foreign flag vessel or a US flag vessel with an international itinerary comes to your attention, report it to your supervisor and OCM/OEO 301-796-8240 immediately. The Centers for Disease Control and Prevention (CDC) assumes primary jurisdiction for foreign flag (non-US registry) and US flag vessels with international itineraries entering the US and traveling in US waters. See IOM 184.108.40.206.
Reports of illness attributed to travel on an interstate conveyance (plane, bus, train, or vessel) are a shared responsibility of FDA, CDC, USDA, EPA and potentially others. When a report of illness is received, notify OCM/OEO at 301-796-8240 and contact the appropriate Emergency Response Coordinator (ERC) in your District and/or Regional Office immediately. The ERC will contact the CORE Signals Team at CORESignalsTeam@fda.hhs.gov. Please include the CFSAN Division of Field Programs Interstate Travel Program Office on any email correspondence (Bruce.Kummer@fda.hhs.gov). In addition, you are encouraged to share the report with state and local public health officials. The following activities are to be coordinated with local/state public health officials:
Interviews with the ill passenger, family members (well and ill), caregivers, and/or health professional (as appropriate) should be sufficiently probative to hypothesize if the food, water or an environmental transmission is related to the illness. Transmission of illnesses, particularly viral diseases, by ill employees and contaminated environmental surfaces can result in illness carryover between successive trips and should be considered. Factors such as time of onset of symptoms, symptoms, food history for the 72 hours prior to onset of the first symptom, any clinical laboratory results, and other potential exposures should be documented. The carrier should also be contacted to determine if other reports of illness have been received (passengers and employees). Obtain any illness logs from the carrier. The information developed should be evaluated to determine if further follow-up is necessary. On those carriers where a reservation system is used, obtain the names and phone numbers of passengers. It may be necessary for the state/local health authorities, CDC or FDA to contact other passengers to determine if they became ill.
If additional cases are uncovered during these contacts, immediately notify the appropriate ERC in your District and/or Regional Office immediately who will then contact the CORE Signals Team at CORESignalsTeam@fda.hhs.gov and the state and local public health authorities in all of the affected states. FDA will work cooperatively with these authorities and request their assistance in conducting an epidemiological investi-gation and collecting patient specimens. Note: If at any time the local/state public health officials are unable to assist with an investigation, notify CORE Signals Team at CORESignalsTeam@fda.hhs.gov who will contact CDC and request assistance in the epidemiological investigation.
One of FDA's functions is to assist local, State, and other Federal agencies in conducting investigations, collecting samples, and conducting plant inspections if warranted.
In addition to state and local health departments, the following federal agencies may also become involved in investigating foodborne disease outbreaks:
- U.S. Department of Agriculture (USDA)
- Centers for Disease Control and Prevention (CDC)
- Environmental Protection Agency (EPA)
Whenever a complaint is received involving any meat containing product, including such items as soups, combination infant foods, frozen dinners, etc., evaluate the need to contact USDA. Most products containing red meat or poultry are regulated by USDA. The exceptions include:
- Products containing meat from game animals, such as venison, rabbits, etc.;
- Meat-flavored instant noodles;
- The product "pork and beans" (which contain only a small amount of pork fat and is regulated by FDA); and
- Closed face sandwiches.
Determine from the consumer if there is a round "shield" on the label with the USDA Establishment Number. Alternatively, the establishment number may be identified in the lot number. Red meat products under USDA jurisdiction will often contain the abbreviation "EST" followed by a one to four digit number; poultry products under USDA jurisdiction will contain the letter "P" followed by a number.
IOM 3.2.1 and 220.127.116.11 provide information for reporting suspected outbreaks to USDA and CDC. In addition, FDA and CDC have an agreement that FDA will be immediately advised whenever CDC ships botulism antitoxin anywhere in the United States or its possessions.
Whenever the source water is suspected as a likely origin of the agent of an illness outbreak, Environmental Protection Agency (EPA) should be notified. For example, when investigating a foodborne outbreak on a vessel passenger conveyance, you may find the water used in food preparation to be from a land-based source or from an on-board water treatment plant. Both of these sources would fall under EPA jurisdiction. See IOM 3.2.11.
A farm investigation of a raw agricultural commodity (RAC) may be conducted as a result of a traceback conducted during a foodborne outbreak investigation that implicates a specific farm or ranch, packing house, and/or any other operations involved in handling the RAC. Generally CORE (Coordinated Outbreak Response and Evaluation) would coordinate a farm investigation in conjunction with a District Office (domestic produce) or a team of investigators (foreign produce). A District Office may also initiate a farm investigation as follow up to a positive produce sample or be directed by either CFSAN or ORA HQ through an assignment to conduct follow up to a positive sample to mitigate the public health impact when the farm is still in production and the product must be removed from commerce. The goal of the investigation is to gather information, observe and document practices that may have led to the growth and survival of pathogen specific contamination of produce, and that will support regulatory action, if appropriate
A team approach is utilized for a farm investigation (see IOM 18.104.22.168 Team Investigations). A Lead CSO should be identified from the District Office and who has attended the FDA ER321 Produce Farm Investigation Course. A minimum of 3 team members should participate and ideally all members should have produce farm training and/or produce farm inspection experience. The appropriate State Regulatory Agency having jurisdiction over produce farms should be notified and invited to participate. Additional Subject Matter Experts (SMEs) may be added to provide needed expertise such as wildlife, soils, agricultural water, or epidemiology. CORE, CFSAN Produce Safety Staff, and/or ORA HQ may assist with identifying appropriate SMEs and providing technical guidance during the investigation.
The implicated grower should be notified in advance of the investigation as he/she or a representative of the grower will need to be present to provide information to assist the investigation. Generally, a 482 will be issued to the grower or packing house, if different. If the investigation expands to fields not owned by the grower, a new 482 must be issued to those growers. Please see IOM 22.214.171.124 Team Investigations for additional information.
CORE is currently leading a workgroup to develop a Standard Operating Procedure (SOP) to conduct environmental assessments at produce farms which should be finalized in 2014. This SOP will supplement this guidance and is intended to be utilized by CORE when requesting farm investigations associated with foodborne outbreaks. A link will be provided in the electronic version of the IOM when available.
A variety of environmental samples may be collected during a farm investigation, including environmental swabs and water from both the field and the packing house, and soil and wildlife scat samples from the growing environment. Do not collect human fecal matter, the FDA Laboratories are not equipped to analyze these. If it is felt that these samples are necessary to inform the investigation, arrangements may be made through your State counterparts or CDC to collect these. Instructions for collecting soil and water samples on farm investigations are found in IOM Ch. 4, in the Salmonella Sample Schedule Chart 1 and covered in ER321. All environmental samples are labeled Investigational. Use the product code builder to identify the proper code for the type of environmental sample collected, including swabs, soil, water, and animal scat; do NOT use the product code of the implicated produce for environmental samples. Produce samples taken from the field or prior to packing (i.e. not finished product) are labeled as investigational; finished product, i.e. have completed processing on the packing line, are labeled “official”. Use the appropriate product code for produce samples. Note: Normally produce is not collected from the field unless a for-cause observation is made or if it is requested as part of an assignment or directed by CORE or ORA HQ. The District should be consulted prior to collecting pre-processed produce.
FDA Form 3623, the Farm Investigation Questionnaire (FIQ), must be completed for all farm investigations, as covered in ER321. Some portions may not be applicable, such as use of biosolids; these questions may be marked as N/A. However, questions for practices that may be used but are not currently in use should be completed by use of interview techniques with the grower to the extent possible. The FIQ should be completed on site to ensure all information is collected and submitted to CORE and/or the CFSAN Produce Safety Staff if requested, and included in the EIR as an Attachment. To avoid duplication in the EIR, the FIQ may be used to provide information under the “Manufacturing Processes” section by either reference or cutting and pasting into that section. A short summary and flow diagram(s) describing the steps from planting through harvesting and/or packing should be included along with this.
There are two ways you can record 483 observations for a produce farm or packing house: use a hard copy FDA 483; or use an electronic non-Turbo version. Do not use Turbo 110 citations for raw agricultural produce operations.
Do not cite or paraphrase a GMP/Part 110 regulation even without the statutory reference.
State what you observed in terms of relating the observation to a 402(A)(4) charge, i.e. link to a potential route of contamination. The following is an example of a citation of a significant observation at a packing house:
The carpeting on the dump tank where cantaloupes are received from the field is visibly soiled. The cantaloupes come in contact with the carpet. Carpet is not a cleanable surface and provides harborage for pathogens of concern.
OFFO/DFFPOI/POB presented a Webex which covers this, and may be viewed at:
For farm investigations, if a 482 was issued, an EIR should be completed. Otherwise, per IOM 8.1, an investigation memo should be written covering the reason for the investigation, a description of investigative activities, the findings, the grower’s response if provided, and any recommendations for mitigation or regulatory action. If an outbreak is on-going and the information is needed immediately, it may be necessary to prepare a memo to submit to CORE prior to completing the EIR.
Investigator kits with proper equipment should be maintained in the district to facilitate immediate investigation of foodborne outbreaks. The kits should be re-stocked on a schedule recommended by FDA laboratory personnel to ensure continued sterility of sampling equipment. A supply of commercially available environmental sampling swabs containing transport media should be readily available as part of the investigation kit. These tubes provide a transport medium that will help preserve the environmental and food swabs.
If an alert or complaint indicates a large outbreak, inform your servicing laboratory immediately that samples will probably be collected and give the approximate time they are expected to arrive at the laboratory. This will assist laboratory managers planning work schedules, equipment and supplies.
Each district may have individuals specifically trained in epidemiological investigations who can provide advice on investigations. If not, consult with OCM/OEO at 301-796-8240 and the state and local public health authorities.
Health professionals, hospital personnel, or consumers may report suspected cases of foodborne illness. Regardless of the source of the report, the diagnosis must be verified by a thorough case history and, if possible, by examination of appropriate food samples and clinical specimens. This verification is done by public health professionals.
Upon contacting the affected person, identify yourself and explain the purpose of the visit or call. Neat attire, pleasant manner of speech, professional attitude and confidence in discussing epidemiology and control of foodborne illnesses are important in developing rapport with an affected person or family. Exhibit a genuine concern for persons affected, and be sincere when requesting personal and confidential information. Communicate a sense of urgency, and emphasize the positive contribution already made by the complainant toward the control and prevention of foodborne illness.
Set your level of communication based on the person being interviewed. Tact is essential. Phrase your questions so the person(s) interviewed will describe their illness, and the foods and events which they feel were associated with it, in their own way. Use open ended questions. Never suggest answers by the way you phrase your questions.
Ask specific questions to clarify the affected person's comments. Realize people are sometimes sensitive to questions about age, gender, special dietary habits, ethnic group, excreta disposal and housing conditions. Phrase questions thoughtfully. Some information may usually be deduced from observations, but if doubt remains, confirm your hypothesis by asking questions. Information on recent travel, gatherings, or visitors may indicate common sources or events.
Gather information about all meals and snacks eaten seventy-two hours before onset of illness. The food, even the meal, which precipitated the illness, might not be obvious. The type of illness will sometimes give a clue.
If the first and predominant symptoms are nausea and vomiting, concentrate questions on foods eaten recently.
If the first and predominant symptoms are diarrhea and abdominal cramps, foods eaten six to twenty hours before onset of illness are suspect.
If diarrhea, chills and fever predominate, foods eaten twelve to seventy-two hours before onset of illness are suspect.
Remember that these suggestions relate to common foodborne illnesses. The more unusual illnesses often present different clinical patterns. For instance, some illnesses such as Typhoid Fever and Hepatitis A, have incubation periods greater than 72 hours. Refer to IOM Exhibit 8-6.
Use this detailed interview approach with every person identified in the initial complaint or alert, even though some may not have been ill, until you have sufficient information to determine if there is a foodborne disease outbreak.
Physicians' and hospitals' records can be useful in verifying reported signs, symptoms and other clinical data and can sometimes rule out the possibility of foodborne illness. See IOM 5.10.5, IOM 8.2.6 and IOM Exhibit 8-5.
CAUTION: Never taste any of the food products, and handle all samples with caution to prevent accidental ingestion of even minute amounts of the contaminated or suspect product.
During investigations of foodborne diseases, cooperate with other health officials in collecting samples of items that may be associated with the outbreak.
Use a menu or data from an attack-rate table to determine which of the foods from the implicated meal are most suspect and collect samples of the suspect foods. Check storage areas for items that may have been overlooked. Check garbage for discarded foods or containers. Suspect foods often are discarded by an operator if he thinks someone may have become ill as a result of eating in his establishment. Because one of the primary tasks of the investigator is to prevent further illness, take appropriate action to prevent distribution or serving of any suspect food until it has been proven safe. If no foods remain from the suspect meal or lot, try to collect samples of items prepared in a similar manner, but subsequently to the suspect lot. Collect ingredients or raw items used in the suspect food. Determine supplier, distribution, and code information on ingredients and packaged foods to aid any investigation of the same lot in distribution channels.
Collect samples aseptically. If foods are to be examined for organophosphate pesticides or heavy metals, do not use plastic containers. Use glass jars with foil lined lids because substances from the plastic can leach into the food and interfere with analysis.
The following are examples of articles normally collected:
- Remaining portions of all suspect foods;
- Parent stocks of suspect foods;
- Insecticides, rodenticides, or other poisons which may be involved.
- Suspect food containers such as cans, bottles, etc.;
- Utensils or materials used in the preparation and storage of the suspect food;
- Table scrapings and food residues from equipment such as slicing machines, cutting boards, etc.
NOTE: Clinical specimens such as vomitus, stools, swabs of nasal and throat passages or open sores or lesions of food workers are collected by local, state, or CDC health officials or private physicians.
In general, follow the IOM SAMPLE SCHEDULE in Charts 1, 2, and 3 (IOM, Chapter 4). Where only small amounts of items remain, such as bits of leftovers, empty containers with adhering particles, etc., collect all or as much as possible by scraping from utensils, equipment or containers. It may also be necessary to collect the empty containers. See IOM 126.96.36.199.
Record the temperature of the room, refrigerator, or warmer in which the food was stored, and record the temperature of the food that remains after a sample is collected.
Inform the laboratory of the type and number of samples, and discuss methods to preserve and transport samples, time of arrival, and the person who will receive the shipment.
Samples of products frozen at the time of collection should be maintained frozen until analyzed. Samples of perishable foods, which are not frozen at the time of collection, should be cooled rapidly to a temperature of 4.4oC (40oF) and maintained at this temperature if they can be analyzed within eight hours. If analysis cannot be started within eight hours, and you suspect microbial contamination, contact your servicing microbiology laboratory for proper handling procedures.
Transport refrigerated or frozen samples to the laboratory in insulated containers, packed with an appropriate refrigerant to maintain the desired temperature during transit. Send samples to the laboratory by the most expeditious means. Clearly mark: "PERISHABLE FOOD SAMPLE FOR MICROBIAL EXAMINATION - RUSH," "PRIORITY." Label specimens according to applicable regulations governing transport of hazardous material. See IOM 188.8.131.52.6.
If the suspect food is a commercial product, examine the original package or container for coding information to identify the place and time of processing. Your district may notify all agencies responsible for regulating the products alleged or suspected to have caused the illness. Collect additional packages bearing the same code number for analyses for microorganisms, toxins, seam defects, vacuum, leaks, or other conditions. Be as specific as possible in requesting the type of analysis.
Conduct a preliminary evaluation of your epidemiological data as soon as possible. If your data suggests an outbreak has occurred, develop a hypothesis about the causal factors. Test your hypothesis by obtaining additional information to prove or disprove its validity.
An outbreak is two or more cases of a similar illness shown by an investigation to result from a common exposure, such as ingestion of a common food. Single cases of certain rare and serious conditions, such as botulism, elicit an outbreak like response. This definition of an outbreak was adopted from the Council to Improve Foodborne Outbreak Response (CIFOR), an organization supported by both CDC and FDA.
Sometimes it will be obvious from an initial report that a foodborne disease outbreak has occurred, simply because of the number of individuals displaying certain symptoms at or near the same time. Many complaints, however, involve illness in only one or two individuals, and determining a particular food was responsible, or its consumption and the onset of illness was only coincidental, is often difficult. Certain diseases that are highly communicable from person to person, such as epidemic viral gastroenteritis, or those associated with a common place, such as carbon monoxide poisoning, may simulate a foodborne illness.
If additional complaints connected with the same food or eating establishment are received, food is almost certainly involved. A food-related or enteric disease alert/complaint log assists in determining if similar complaints have been received.
Time associations primarily refer to onset of similar illnesses within a few hours or days of each other. Place associations deal with buying foods from the same place, eating at the same establishment, residing at the same place, or attending the same event. Person associations have to do with common experiences, such as eating the same foods or being of the same age, gender, ethnic group, occupation, social club, or religion. Once some of these associations become obvious, verify the outbreak by identifying and interviewing other individuals who were at risk by virtue of their association with the ill persons.
If the outbreak affects a large number of individuals or food establishments, consult with your supervisor regarding the need to seek assistance from other health professionals. A team consisting of an epidemiologist, microbiologist or chemist, sanitarian, and others may be required to make a sufficiently detailed foodborne illness investigation. Such personnel may be provided by local, state or provincial, or national agencies concerned with health, food and drug, environment, fish or agriculture.
Seek and interview additional individuals both ill and well, who had time, place, or person associations with the identified cases. If the suspect meal was served during a particular occasion, determine the name of the person in charge. That person may have a list of names, addresses, and telephone numbers of persons who attended. Obtain menus of suspect meals as soon as possible. Additional cases may be identified by checking reservation books and credit card receipts. Review the districts food-related, enteric disease alert/complaint log for recently received complaints which may be related to the outbreak. Consult with your supervisor as to further contact with other health agencies, hospital emergency rooms, poison control centers, and local physicians to find additional cases. At this stage of the investigation, interviews can be accelerated by reviewing the event itself to stimulate each individual's memory. Inquire about specific symptoms known to be common to the suspected syndrome, and mention each food served at the event or meal.
The number of individuals to be interviewed depends on the proportion of attendees who are probably affected. As a rule of thumb, if no more than 100 people attended the meal, an effort should be made to interview everyone. If several hundred were present, a random, representative number should be interviewed.
Prepare a separate FDA 3042, Food Illness Investigation Report, for each person interviewed. See IOM Exhibit 8-7. The FDA 3042 is intended as a guide to supplement a complete narrative report. Do not be restricted to this form in obtaining details during investigations. Information can be extracted from this form to compile an Attack Rate Table to pinpoint the suspect food. See IOM Exhibit 8-8.
When botulism or other foodborne outbreak is reported, and an establishment is inspected, the initial impact of the incident can create confusion at the plant, and conflicting instructions if too many individuals become involved.
To reduce the confusion, one investigator should be designated as the team leader. A supervisor should be the coordinator for overall district activities, and the district contact for headquarters personnel. All communications from FDA field or other offices to the firm's management should be channeled through the supervisor. The lead investigator should be responsible for all phases of the physical inspection of the facilities, and briefing the supervisor as to his progress. See IOM 184.108.40.206.2.
Upon arrival at the establishment where the suspect food was processed or prepared, the implicated meal was served, identify yourself to the person in charge and state your purpose. Emphasize the purpose of the investigation is to determine what contributed to the outbreak, so preventive measures can be taken. Attempt to create a spirit of cooperation. Consider the position, feelings, and concerns of the manager and his staff; defensive reactions are common.
Many factors could have contributed to contamination before foods came under the control of the manager. Assure him these possibilities will also be investigated. Inform the manager of the activities proposed and benefits which may be gained for educating his workers.
Review of distribution records and examination of warehouse stock are two important aspects of a botulism follow-up inspection. Each of these operations should be monitored by an investigator reporting directly to the team leader. These two monitoring investigators are responsible for all reports from their assigned areas, regardless of the number of investigators assisting them. Field examination should also include an inventory by code of all stock on hand. When conducting field examinations, follow instructions in IOM Sample Schedule Chart 2 (IOM, Chapter 4).
When preparing the report, follow instructions in IOM 220.127.116.11.1.
If a food is already suspect, interview separately all persons who were directly involved in processing, preparing, or storing of the food and others who could have observed preparation and storage. Ask questions in a sequence that discloses the flow of food from the time it was received until it was served or distributed. Especially inquire about foods that were prepared several hours or days before being served with the suspect meal. Ask similar questions, suitably modified, of the managers or workers who were involved in producing, transporting, processing, preparing, or storing food at other levels of the food chain, as well as individuals who prepared the food at home.
Food workers who fear criticism or punitive action because of their possible role in the outbreak do not always accurately describe the food handling as it actually happened. Their descriptions should be plausible, account for possible sources of contamination, and indicate possibilities of survival and potentials for growth of pathogens. If the description does not contain all the information desired, rephrase the questions and continue the inquiry. Seek confirmation of one person's story by talking to others who have knowledge of the food operation, or by watching the food preparation or processing practices. Be alert for inconsistencies among the accounts, as told by different individuals.
It is important to have an understanding of the pathogen and the factors that contribute to the contamination that resulted in the foodborne illness. Some pathogens, such as Shigella, are associated with human fecal contamination, while other pathogens, may be more commonly associated with a particular food source (e.g. raw meat and E. coli O157:H7). Exhibit 8-6 and microbiologists can help provide useful information on sources and contributing factors.
Pests are a possible contamination source and can be an indication of poor hygiene, sanitation, food storage, handling and preparation practices. These pests include certain rodents, flies, cockroaches or other pests that:
- Occur around human settlements.
- Occur indoors as well as outdoors.
- Are attracted to potential sources of pathogens (garbage, drains, excrement, etc.) and to human food.
- Travel back and forth between possible sources of pathogens and food or food contact surfaces.
Evaluate whether a pest is a potential contributing factor to the outbreak by comparing your direct observations of pest activity combined with other evidence of pest activity (excreta, urine, gnawing, etc.) to the above criteria. A pest species that appears to meet all four of the above criteria is a possible source of pathogen contamination. It is helpful to collect specimens of any insect pest that meets these criteria for identification to determine if the pest species is one that is known to carry foodborne pathogens. See Appendix A.
Raw poultry, pork, and other meats are often contaminated when they come into kitchens. If any of these agents are suspected in an outbreak, samples of meat and poultry, meat scraps, drippings on refrigerator floors, and deposits on saws or other equipment can sometimes be helpful in tracing the primary source. Swabbing food contact surfaces of equipment (as tables, cutting boards, slicing machines) which had contact with the suspect food may establish links in the transmission of contamination. This is especially true if a common utensil or piece of equipment is used for raw and cooked foods. Swab these surfaces with sterile swabs, moistened with a sterile solution (such as sterilized 0.1% peptone water or buffered distilled water). Break off the tip of the swab into a tube containing 5 to 10 ml of this solution or into a tube of enrichment broth for specific pathogens. Samples or swabs from air filters, drains, vacuum sweepings, food scrap piles, dried deposits on equipment, and dead ends of pipe lines may reflect the presence of organisms previously in the establishment.
Evaluate the cleanliness, manner, and frequency of cleaning equipment. Seek possible routes of cross-contamination between raw and cooked foods. As ingredients may be the initial source of pathogens, determine which were added before, and which were added after any cooking or heat processing.
Workers can be a source of foodborne pathogens. Enterotoxigenic Staphylococcus aureus strains are carried in the nostrils of a large percentage of healthy persons. They are also found on the skin and occasionally in feces. Clostridium perfringens can be recovered from the feces of most healthy persons. Workers are sometimes infected with other enteric pathogens. Employee food safety training and knowledge should be investigated. Poor hygiene practices among food workers (e.g. not washing their hands), continues to be a major contributing factor to foodborne illnesses. See IOM Exhibit 8-6. If the same type of pathogenic organism is recovered from a fecal specimen of a worker and the suspect food, do not immediately conclude the worker was the source. A worker who ate some of the implicated food could be one of the victims. A history that includes a skin infection (boil or carbuncle) or a gastrointestinal or respiratory disturbance preceding the preparation of the suspect food would be more incriminating. Employee attendance and sick leave records may provide additional information.
Look for pimples, minor skin inflammation, boils and infected cuts and burns on unclothed areas of the body; ask if there are any infections in other areas.
In addition to tracing sources of contamination, the circumstances which permitted survival and growth of foodborne pathogens in the implicated foods must be identified. This information is vital to develop preventive measures. Factors usually contributing to outbreaks of specific foodborne illnesses are cited in IOM Exhibit 8-6. Identify these factors by careful and diligent interviews of food workers; close observation of employees' food handling practices; checking temperatures of foods during processing and equipment in which the foods were held; and by conducting studies to determine time-temperatures relationships during processing and storage. Consider times and temperatures which were involved in freezing, thawing, cooking or thermal processing, hot and cold holding, chilling, reheating, and any other steps in the processing operations. It is important to know the survival and growth characteristics of the pathogen that caused the illness outbreak. For example, viruses do not replicate outside of the body and therefore will not "grow" regardless of the temperature. However, their survival characteristics should be considered. You should consult with a microbiologist or CORE prior to your investigation in order to understand the characteristics of the pathogen and focus on the relevant contributing factors.
Organize and group the data obtained from interviews of both ill and well individuals. From appropriate calculations and analyses, the illness can be classified, the hypothesis tested as to whether the outbreak was associated with a common source, a vehicle can be determined, and the necessity for further field or laboratory investigation can be decided.
An epidemic curve is a graph which depicts the distribution of onset times for the initial symptoms of all cases that occurred in a disease outbreak. The unit of time used in the construction of the graph depends on the disease, or the period covered by the outbreak. For example, use a scale in days or weeks for Hepatitis A; and a scale in hours for staphylococcal food poisoning.
The epidemic curve assists in determining whether the outbreak originated from a common-source, such as food, or person-to-person propagation. A common-source epidemic curve is characterized by a sharp rise to a peak; with the fall usually being less abrupt. The curve continues for a period approximately equal to the duration of one incubation period of the disease. A person-to-person curve is characterized by a relatively slow, progressive rise. The curve will continue over a period equivalent to the duration of several incubation periods of the disease. (Exhibit 8-9)
Determine predominant symptoms by constructing a table as illustrated below:
Frequency of symptoms
|Symptoms||Number of Cases||Percent with |
Symptoms (N = 20)
The percent of ill persons who manifest each symptom is obtained by dividing the number of individuals reporting a given symptom by the number of individuals reporting any symptom (twenty in this example), and multiplying by one-hundred.
This information helps determine whether the outbreak was caused by an agent that produces a neurological, enteric, or generalized illness. Either infections or intoxications will be suggested. Such information can identify suspect foods and indicate appropriate laboratory tests.
The incubation period is the interval between ingestion of a food contaminated with enough pathogens to cause illness and the appearance of the initial symptom of the illness. Calculate this interval for each case. Individual incubation periods will vary because of individual resistance to disease, differing amounts of food eaten, uneven distribution of the infectious agent or toxin throughout the food, and other factors.
The shortest and longest incubation periods give a range. Calculate the median incubation period, the mid-value of a list of individual incubation periods when ordered in a series from the shortest to the longest or the average of the two middle values if such series contains an even number of values. The median, rather than the mean, is used because the former is not influenced by exceptionally short or long incubation periods which are sometimes reported in outbreaks of foodborne illness.
The median and range of the incubation period, coupled with information regarding predominant symptoms, form bases upon which to judge whether the disease in question is an infection or intoxication and thereby determine what laboratory tests should be done.
See Exhibit 8-6.
Complete the Food-Specific Attack Rate Table. It provides an easy way to compare the percentage of ill persons who ate each food with the percentage of ill persons who did not eat each food. The attack rate table is useful in identifying the food responsible for an outbreak or illness. This food will usually have the highest attack rate, percent ill, in the column for persons who ate the food and the lowest attack rate in the column for persons who did not eat the food; it will also have the greatest difference between the two rates. See IOM Exhibit 8-8.
Traceback investigations are important epidemiological tools that are used to determine the source of food implicated in foodborne outbreaks. Traceback investigations may prevent further sale and distribution of contaminated food. Commonly, states or local government agencies conduct the initial epidemiological investigation of foodborne outbreaks and identify suspect (interstate) product(s) requiring tracebacks. In some cases FDA may be asked to assist another agency with a traceback investigation.
Any requests for traceback investigations received by a District Office related to a foodborne outbreak should be referred to the appropriate ERC in your District and/or Regional Office who will then contact the appropriate CORE team. CORE will issue traceback assignments to the appropriate district(s) and coordinate inter-district assignments for traceback investigations. The field should use the FDA Guide to Tracebacks of Fresh Fruits and Vegetables Implicated in Foodborne Outbreaks, dated April, 2001, unless otherwise directed by ORA HQ or CORE.
Your district will follow Field Management Directive FMD-119 for proper reporting of epidemiological investigations. Promptly submit a complete narrative of the investigation in English (IOM 1.1), including references to exhibits, samples, medical records, and laboratory reports. There is no prescribed reporting format, but it should be in a logical order, see IOM Exhibit 5-17. With the inclusion of investigative memos in Turbo EIR, Turbo can be utilized to prepare these memos. See the Turbo EIR Quick Reference Guide for detailed information. See also IOM 8.10.
Submit copies of any written reports and documents for all INJURY or ILLNESS complaints involving all CFSAN products (see section 8.2 and 8.4.5) to:
Food and Drug Administration
CAERS Staff (HFS-700)
5100 Paint Branch Pkwy
College Park, MD 20740
Attn: CAERS Monitor
Illness/injury complaints involving special nutritional products (refer to IOM 18.104.22.168) must be accompanied by a completed FACTS Adverse Event Questionnaire (Exhibit 8-1) when forwarded to CFSAN.
If additional follow-up on any complaint involving a CFSAN product is necessary, the Division of Field Program Planning and Evaluation (HFS-635) will issue an assignment.
- "Procedures to Investigate Foodborne Illness" Int'l Assoc. of Milk, Food and Environmental Sanitarians, Inc., Ames, Iowa 50010.
- "Diseases Transmitted by Foods" CDC, Atlanta, GA. 30333.
- "Procedures to Investigate Waterborne Illness" Int'l Assoc. of Milk, Food and Environmental Sanitarians, Inc., Ames, Iowa 50010.
- "Epidemiology Man and Disease" J.P. Fox, M.D., and L.R. Elveback, PhD, MacMillan Publishing Co., N.Y., N.Y. - 1970.
- FMD 119 - Consumer Product Complaints System.
- Regulatory Procedures Manual Chapters 5 - 10.
- "Control of Communicable Diseases Manual," American Public Health Association, Washington, D.C. 20001-3710.
- FDA Guide to Tracebacks of Fresh Fruits and Vegetables Implicated in Foodborne Outbreaks, dated April, 2001.