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Conducting Effective Foodborne-Illness Investigations.


Hazard analyses during an outbreak investigation must focus on identifying the source and mode by which the implicated food has been contaminated, as well as on the situations that have allowed the contaminants to survive heat processing or other potentially lethal processes and that have permitted or promoted propagation of the pathogen. This article offers practical techniques for detecting such events. The information can be used to prevent further occurrences at the location where a mishandling has occurred and to build a surveillance database. Factors that contribute to foodborne outbreaks can be incorporated into the database, which can guide inspections, hazard analyses, promulgation of food regulations, training of public health personnel and food workers, and education of the public.


Epidemiologic data generated from calculations of rates and statistical analyses may suggest hypotheses of etiologic agent, place of eating, perhaps a meal, and perhaps a food. The task of the field investigator is to prove or refute the validity of these hypotheses, or to gather data from which to formulate other hypotheses.

Investigative Procedures

Anticipating from Initial Data Where to Focus Attention

At the outset of an on-site investigation at the place of a presumed mishandling, investigators should concentrate on contamination, survival, and/or propagation of the etiologic agents under suspicion. If there is a microbial- or chemical-caused disease, contamination with the etiologic agent has to have occurred. If the disease is microbial, either there was no heat process (e.g., fresh produce or shellfish was eaten raw) or the pathogen survived a process such as cooking or heat processing or the contamination occurred after the process. If the disease is bacterial, the pathogen (unless highly virulent or affecting highly susceptible persons) must propagate to attain a population or to produce a quantity of toxin that overwhelms the susceptibility/resistance threshold of the host. If the disease is parasitic, the parasite may have to develop into an infectious stage. Therefore, at the sites of production, processing, and/or preparation, priority activities will be

* to find the source (whether within the food establishment or from before the food arrived there) and mode of contamination;

* to determine whether the process killed the pathogens, reduced their populations, or permitted survival; and

* to determine whether the pathogen propagated rapidly, slowly, or not at all.

With this attitude and with appropriate equipment and supplies, an investigator is ready to work on site [1]. Table 1 shows sources and modes of contamination, and further help is available in a manual of procedures for investigating foodborne illness; the procedures involve anticipating contamination, survival, and growth [1].

Proving the Illness Has Been Caused by the Etiologic Agent Under Consideration

In this step, investigators will need to obtain stool, blood, or other appropriate specimens from those who are ill and whose syndrome and incubation period are typical of the disease under consideration. The specimens then can be analyzed for the suspected etiologic agent [1,2]. This step is essential in confirming a diagnosis; otherwise the investigation will result in the classification "unknown etiology." After isolation of a pathogen, if applicable (as in cases of Salmonella and Escherichia coli contamination), investigators should request that isolates be typed to identify the serovar or strain. Further identification of the strain is possible with markers such as phages, DNA probes, and antibiograms, or with a number of other techniques [1].

Confirming the Vehicle and Eliminating Other Possible Vehicles

The next step is to calculate attack rates for those who have eaten specific foods and those who have not. Or, from information on food histories, the investigators will need to calculate percentages, if this has not been done, for those who are ill and for those who are well (controls) among people who

* have attended a common event,

* have eaten a common meal, or

* have eaten the same food item from information on food histories.

The symptoms of people classified as ill must comply with a case definition that is developed from the syndrome under investigation. It is appropriate to calculate these data with both narrow and broad case definitions. A narrow case definition might be laboratory-confirmed cases; a broad case definition would include those cases as well as cases involving diarrhea or other appropriate signs and symptoms that have occurred within the incubation period of the disease under consideration. If both calculations suggest the same vehicle, confidence that the vehicle has been identified is high. The investigation then can focus on this vehicle. If, however, one calculation indicates a different vehicle than the other, the investigation should look at the processing and preparation of the foods that both calculations have suggested as vehicles. Additional statistical calculations can evaluate the strength of the association between disease and consumption of a suggested vehicle (e.g., relative risk, or odds ratio), as well as the probability that the differences in rates occurred by chance (e.g., Chi-squared or Fisher's exact probability test). These calculations provide information from which to form a hypothesis about a vehicle and supportive data.

If a pathogen (e.g., Salmonella enteritidis) has been isolated from a specimen, certain foods (e.g., eggs) might come under initial suspicion because of the history of contamination of eggs by salmonellae. Nevertheless, the vehicle must be proven or refuted by subsequent laboratory testing and on-site investigation. To implicate a particular food as a vehicle, investigators must eliminate from consideration all other possible vehicles and reservoirs. For example, animals of all sorts can be infected with salmonellae, and their meats or products (e.g., eggs, milk) may be contaminated with these bacteria. If poultry and red meat have been served at the same meal or have been eaten by people meeting the case definition, consider these foods as potential vehicles despite an initial hypothesis of eggs, for example, as the vehicle. Raw poultry, meat, seafoods, and eggshells can serve as sources of contaminants. Cross-contamination via workers' hands, equipment, or utensil surfaces that come into contact with those sources may spread the pathogen from raw to ready-to-eat foods of any type.

Another way of implicating vehicles is to collect samples of prepared or processed foods and test them. In identifying sources or modes of contamination, it can be helpful to take

* samples of raw products used as ingredients (e.g., beef, pork, turkey chicken, eggs);

* swabs of equipment surfaces; or

* samples of products during particular stages of processing.

Whenever pathogens are isolated from foods, investigators should definitively type them and compare them with strains isolated in specimens from ill persons. For association, the strains found in patient specimens and in food should be identical. Isolation of the strain of pathogen under investigation or large quantities of this organism from any of the processed or prepared leftover foods provides evidence that the product was the vehicle if this conclusion is supported by on-site confirmation of contamination, survival, and/or propagation.

If investigators collect samples of foods--which, typically, they should do--they should take particular care in selecting samples and in interpreting the test results. Collection of samples during outbreak investigations is not like random sampling of end products to find defectives in a production lot. Judgements should be made to select items that might have been contaminated and that might remain so in the suspected place of mishandling or use. Selection of an item or site to be sampled should be based on the following criteria:

* observations,

* measurements,

* information obtained from discussions with establishment staff, and

* a knowledge of typical sources and usual modes of contamination for the pathogens under consideration (Table 1).

Contamination of a food item may occur at specific sites on the item rather than throughout:

* If an item has been rolled or pushed across a contaminated surface (e.g., a table or cutting board), large portions of the surface but not the interior may have become contaminated.

* If a food has been handled by a worker, contamination may be present only on the portion of the surface that has been touched.

* If a fly or other insect has walked over a food, only a small, random, zigzag trail on the surface may have become contaminated.

* If the food has been sliced, the first few slices may be contaminated more heavily than the next slices, and the last few slices may not be contaminated at all.

* If a fork or thermometer has been contaminated, the site of puncture and the internal region along the channel may be the only portions contaminated.

* If solid-food mixtures have been tossed, stirred, or otherwise mixed, contaminants may be spread throughout the mass, but not always homogeneously.

* If liquids are mixed, there is a greater likelihood that the contamination is homogeneously distributed in the solution.

* If multiple dishes or containers of a food are prepared, they may not all be contaminated, or they may not be contaminated to the same extent.

These examples of site-specific contamination are not the only ones possible, but they do illustrate the need for care in selecting items for sampling, as well as in selecting the regions on the items to be sampled.

The thickness of the food mass and ambient storage temperature (e.g., [less than]32[degrees]F, 32-50[degrees]T, 70-120[degrees]F [greater than]l30[degrees]F) greatly influence growth of pathogenic bacteria. (Ambient storage temperature may mean freezer, refrigerator, room or outdoor, or hot-holding temperature.) There probably would be no growth below 32[degrees]F, slow growth over several days between 32[degrees]F and 50[degrees]F rapid growth between 70[degrees]F and 120[degrees]F, and no growth above 130[degrees]F. Furthermore, the depth of the food in storage containers during cooling significantly influences bacterial growth and regions where multiplication is likely to occur. As the depth increases, the likelihood of bacterial growth increases, resulting in larger populations in the center of the mass, if contaminants are present there. The manner in which the food has been served (e.g., cold, room temperature, warm, or hot) further influences the quantity of pathogens present. Also, the manner in whic h the food was stored during the interval between serving and eating influences further growth of pathogenic and competing bacteria. This factor means that when the food is served, populations of an etiologic agent may be either greater or less than populations present at the time the food actually is eaten. Pathogens can even be eliminated by overgrowth of competitive microbes.

Oxidation-reduction conditions around and within the food (which are determined by food mass, processing, and packaging or storage container) also affect the growth of pathogens. This factor dictates which kinds of bacteria (i.e., aerobic, anaerobic, micro-aerobic, or facultative) can grow or grow well.

From such information, it should be clear that the possibility of multiple vehicles in a single outbreak is quite remote. Each item would have to be contaminated with a highly infective pathogen from an ingredient or by handling and not subsequently be heated. Otherwise one of the following situations would have to occur:

* An initially contaminated food has cross-contaminated other foods.

* Different foods have had contact with a contaminated piece of equipment (e.g., cutting board, grinder, slicer, table).

* An infected person has contaminated each food item.

Then the contaminant would have to survive all subsequent processing (e.g., cooking) of each item. Furthermore, each item would have to be subjected to time-temperature abuse (e.g., being left at room temperature, being stored in large containers in a refrigerator) that has allowed multiplication of the pathogenic bacteria to populations sufficient to cause illness. The chance is small that all these events will occur sequentially in multiple food items.

When interpreting the results of the analysis, investigators should consider all the situations and conditions described above. Additional limitations of sampling and testing have been described elsewhere [3]. It is not always possible when pathogens are present--even large populations of pathogens-- to isolate them from samples of epidemiologically implicated foods. Therefore, the fact that pathogens have not been found in epidemiologically implicated foods does not necessarily mean that the illness was caused by viruses. The etiologic agent, along with a host of other pathogens, may not have been recovered for any of the following reasons:

* an inappropriate sample has been taken

* the wrong sample site has been chosen on an appropriate food sample,

* the results have been affected by the environmental conditions of the food before and after it was served,

* the wrong agents have been tested for, or

* the laboratory methods used were not effective.

The statistically and/or laboratory-confirmed vehicle should be further proven by observations and measurements that demonstrate the biological plausibility of contamination, survival, and/or proliferation (as applicable) of the etiologic agent while disproving the role of other suspected or possible vehicles. Investigators should make these observations and measurements at all sites where mishandling or mistreatment of foods may have contributed to the outbreak.

Based upon observations and discussions, investigators should draw a flow diagram of the processing or preparation of each food that is being considered as a possible vehicle. The diagram should start with each ingredient at receiving and should use rectangles (enclosing titles that indicate operations or activities) for each step that follows until the food is either shipped out or eaten.

Identifying (If Possible) the Source and Mode of Contamination

The most common direct sources of food-borne pathogens are incoming raw foods and workers who handle foods. The mode of contamination may be direct contamination from one of these sources, or a variety of processing and preparation activities may convey contaminants from a source food to other foods. If it is likely that a food product has been contaminated after the food has been subjected to a process potentially lethal to the contaminant, investigators should evaluate the mode of contamination. They can do so by

* interviewing managers about sources of foods and steps in processing and preparation;

* interviewing food workers who were involved with processing and preparation and interviewing others who may know about these situations;

* observing operations (but realizing that workers will be on their best behavior while being watched and that managers may have cautioned workers beforehand to use modified practices); and

* collecting samples of epidemiologically implicated foods or other foods that may have been sources of cross-contamination.

Raw Foods

Incoming raw foods are common sources of Campylobacter jejuni, Cyclospora cayetenensis, Salmonella, Vibrio parahaemolyticus, Yersinia enterocolitica, and several other pathogens. Investigators may conclude that raw food is the source of the outbreak if foods have been eaten raw, if raw ingredients have been incorporated into unheated foods, if foods have been lightly heated for culinary purposes, or if foods have been insufficiently cooked. Raw foods also can contain bacterial spores (e.g., Bacillus cereus, Clostridium botulinum, Clostridium perfringens), which survive typical cooking and pasteurization (although they do not survive properly calculated retorting). In this kind of outbreak, too, the raw foods are the likely source. Furthermore, raw foods can contaminate other foods if they come into direct contact with those foods or if their juices drip, seep, or flow onto the other foods. Investigators should observe handling and storage operations for these possibilities. Proof is obtained by sampling the f oods under suspicion, testing them for pathogens, typing isolates, and comparing the strains with those isolated from patients' specimens.

Cross-contamination commonly occurs when a food worker handles a contaminated raw food and then, without intervening effective handwashing, handles cooked foods, ready-to-eat foods, or an ingredient in a food that will not subsequently be heated. Thus, investigators should evaluate the possibility that processing or kitchen personnel have spread the pathogens by observing kitchen practices and by interviewing personnel about their practices.

In addition, cross-contamination can occur when a contaminated raw product is processed or prepared on equipment (e.g., cutting boards, slicers, grinders, mixers, tables), on surfaces, or with utensils (e.g., knives) that are used subsequently for ready-to-eat foods without intervening washing and sanitizing. Furthermore, cleaning cloths, sponges, and other cleaning aids can spread pathogens from surfaces soiled by raw foods to surfaces used for foods that are not subsequently heated. If a cleaning item remains damp between uses, the contaminating bacteria can multiply These possibilities can be evaluated by swabbing (with sterile cotton-tipped swabs or sterile sponges) of equipment surfaces or of other items that may have helped spread the pathogen. Isolates must be definitively typed to be useful in determining the source and mode of contamination. Investigators can modify their flow diagrams with a note or symbol according to whether ingredients are expected or initially confirmed to be contaminated.


Human beings are reservoirs of certain food-borne pathogens (Table 1). For the most part, human carriers have not played a major role as sources of contamination. Exceptions include persons infected with Salmonella typhi, Shigella, hepatitis A virus, Norwalk-like viruses, enteric viruses (which are host-adapted to human beings), Staphylococcus aureus, and Streptococcus pyogenes. Even when other kinds of contaminants are involved, the possibility of human carriers should not be ignored. Investigators may need to prove or eliminate the possibility that ill persons, carriers, or colonized persons have contaminated the food.

An important step is to interview all food workers who have handled the foods under investigation. Investigators must determine whether any workers have been ill with diarrhea, have had other symptoms of an enteric illness, or have had skin lesions either before or during preparation of the food or meal in question. Supervisors should be questioned and absentee records checked to confirm workers' answers. Because a carrier may remain infected with salmonellae, shigellae, or other pathogenic enteric bacteria for several weeks, the history of diarrhea should extend back two to three months. Also, workers should be questioned about contact with other people (e.g., family members) who have recently been ill with diarrhea or contact with pets (e.g., dogs, cats, turtles, fowl) that may have been infected. Investigators should try to discover whether the workers had bare-hand contact with ready-to-eat foods or with ingredients that were not heated, and should attempt to get an impression of typical handwashing and personal hygiene practices. Also, it is important to learn whether the food workers, ill or not, have eaten the epidemiologically implicated food or handled raw foods of animal origin. If a worker has eaten the implicated food and has become ill during the same interval as the other cases, it is likely that this person is a victim, not the source of the pathogen.

Collect appropriate specimens from food workers who have had an opportunity to contaminate the foods under investigation. Specimens are particularly warranted when

* the food worker has had diarrhea or a skin infection before onset of the outbreak,

* a close contact has had diarrhea or hepatitis,

* there is suspicion of poor personal hygiene practices, or

* there has been a likelihood of bare-hand contact with the epidemiologically implicated food, particularly if the food has not subsequently been cooked.

If enteric illnesses (other than hepatitis A) are under investigation, investigators should collect stool specimens or rectal swabs. If hepatitis A is suspected, they should collect blood specimens. If a staphylococcal food poisoning is suspected, they should collect nasal swabs or skin lesion specimens. Proof of association requires that the patients, the food vehicle, and the worker are found to have the same strain of pathogen.

Epidemiologic data show that the most common event involving workers is bare-hand contact with cooked foods or foods that are not subsequently heated [4,5]. This possibility should be investigated whenever human host-adapted enteric pathogens or staphylococci are under consideration as etiologic agents. To show like modes of contamination on the flow diagram, investigators may wish to insert a comment or symbol into each rectangle that represents an operation [1].

Evaluating and Explaining Time-Temperature Exposures During Cooking

Inadequate cooking is commonly identified as a contributing factor in outbreaks [4,5]. Therefore, whenever a cooked food is contaminated with viruses, parasites, or vegetative forms of non-spore-forming bacteria, one of two things has happened: Either the microorganisms have survived the time-temperature exposures (or other potentially lethal processes), or contamination has occurred after those exposures.

Initially, investigators should get information on the procedures used for all heating processes (i.e., cooking, reheating) by interviewing cooks and others who have a knowledge about the equipment used, its operation, temperature settings, cooking times, and any product temperature measurements. Then investigators should observe potentially lethal processes and test the products and extrinsic environmental conditions to determine whether the pathogens have survived the process.

Better yet is to measure, as far as is practicable, the time-temperature exposures for all possible vehicles the next time that those foods are prepared. Possible vehicles include those implicated by attack rates; those suggested by on-site observations; those, such as poultry, eggs, meat, seafoods, rice, and beans, that are likely to be initially contaminated with pathogens; and those commonly implicated as vehicles. The next time the implicated food is prepared, temperatures should be measured throughout the heating process, and measurement should continue afterwards until the product has cooled to below 130[degrees]F. If feasible, investigators should use thermocouples to measure temperatures at specific locations and should record process times continuously or periodically. Sensors should be inserted into the geometric center of poultry and large cuts of meat. In the case of ground meat and products that are frequently rotated or flipped during cooking (such as scrambled eggs), temperatures should be mea sured at multiple sites. Following microwave heating, temperatures should be measured at regions near surfaces. Surfaces also may be appropriate sites for evaluating the temperature exposures of foods being heated by other means.

After measurements are taken, the data should be graphed. Temperature-value guidelines should be included to predict likely destruction of pathogens. (E.g., at 130[degrees]F, approximately two hours of exposure would be required, and at 165[degrees]F, a few seconds of exposure would be required to kill vegetative forms of pathogenic bacteria. Intermediate amounts of time would be required for temperatures between these values). Higher temperature guidelines (e.g., 212[degrees]F and 250[degrees]F) are needed in evaluating effects on spores. For pathogens of concern, investigators should determine time of exposure within lethal temperature ranges to predict likely survival or destruction (Figure 1). The findings should be evaluated according to published D-values for specific foods at specific temperatures, or z-values can be used to evaluate possible destruction of the pathogens at other temperatures [6]. Comments or symbols about survival can be inserted into the flow diagrams [1].

Measurements of pH and/or water activity of the foods under investigation may provide additional information that is useful in evaluating the lethality of time-temperature exposures. In general, destruction of foodborne pathogenic bacteria progressively accelerates as food products have pH values either lower or higher than the optimum value for growth of the bacteria. Furthermore, if a food with a pH value below 4 is epidemiologically implicated, whether heated or not, investigators should seek an explanation of the means of survival. To do so, they will need to gather information on the type of acid, duration of exposure to heat, and the acid tolerance of the pathogen strain. With dry highly sugared, or otherwise low-water-activity products, considerably longer time-temperature exposures are necessary to kill microorganisms than with moist foods.

Investigators should consider collecting samples of foods before and after potentially lethal processing operations. The samples should be tested for the pathogens in question and/or the quantity of mesophilic organisms to evaluate survival. When interpreting test results, investigators should be aware of

* the site on the food from which the sample was collected;

* time-temperature exposures at that site;

* the environment in which the food was located at the time of sampling (and previously, if determined);

* statistical limitations, according to number of samples collected; and

* limitations of the laboratory tests [3].

In addition, challenge studies that simulate processing situations can provide information on survival or destruction during time-temperature exposures [7]. Such studies should be concluded and interpreted under the supervision of a competent food microbiologist.

Evaluating and Explaining Time-Temperature Abuses in Holding and Storage

Food subjected to slow cooling and room-temperature holding (i.e., inadequate refrigeration) are the most frequent contributory factors in outbreaks of foodborne diseases [4]. Inadequate hot-holding also is a common contributory factor.

Investigators can evaluate food storage and holding with some or all of the following techniques:

* interviewing kitchen personnel about routine practices and any changes in those practices that might have occurred when the meals under investigation were prepared;

* observing cooling, storage, and holding practices during the on-site investigation; and/or

* measuring the temperatures of the implicated products for the entire duration of processing, hot-holding, room-temperature holding, cooling, cold storage, and shipping (if applicable).

Sufficient populations of foodborne pathogens must be present in the vehicle for all the cases associated with an outbreak to have become ill. This usually involves proliferation of pathogenic bacteria at some stage of the food chain. If it has been determined that the heating process was lethal to the pathogen under investigation, the proliferation must have occurred after heating. In the case of eggs, bacterial growth may occur during room or outdoor storage in the shells, but the potential for proliferation increases greatly after eggs are broken--while pooled eggs or batters are held in large containers in refrigerators or while they are held at room temperature awaiting preparation or storage. In an ice cream mix, bacterial growth can occur during the interval between preparation of the mix and freezing if this interval is sufficiently long. Spores can survive cooking of meat, poultry, and prepared food dishes, and contamination can occur afterwards, during handling. Bacterial multiplication also can oc cur during room or warm-temperature outdoor holding or while the food is stored in large containers in refrigerators, particularly if the food is covered with tight-fitting lids or if the containers are stacked. Proliferation also may occur during prolonged warm-holding of these cooked foods if they are held below the maximum temperature at which the pathogens of concern can grow. In rice, beans, and moist pasta, spore germination and bacterial growth occur

* after cooking,

* during overnight refrigeration,

* when the food is held at room or at outdoor temperatures for several hours, or

* when the food is held for several hours in warming devices.

Furthermore, some pathogenic bacteria (e.g., Listeria monocytogenes, Yersinia enterocolitica) can multiply in contaminated foods at typical cold-storage temperatures if the duration of storage is sufficiently long.

Investigators should take time-temperature measurements of foods during operations and under conditions that simulate typical holding of the suspected vehicle. These data can be plotted on graph paper with guidelines at maximum, optimal, and minimal growth temperatures for the pathogens of primary concern and/or with temperature ranges within which pathogenic bacteria multiply "rapidly" (e.g., 70-120[degrees]F), "less rapidly" (e.g., 69-51[degrees]F), or "slowly" (e.g., 32-69[degrees]F). (A few pathogenic bacteria can multiply slowly at commonly used or required cold storage temperatures [e.g., 41[degrees]F]). Potential bacterial growth should be interpreted with reference to the time the food is held within these ranges (Figure 2). Flow diagrams should be modified with the information about the potential for bacterial growth.

Samples of foods should be collected after a holding interval and tested for the presence and quantity of the pathogen under investigation. Also, the samples should be tested for the quantity of mesophilic organisms to show or suggest what the possibilities of bacterial growth are. Measurements of pH and water activity of the food also can be helpful in evaluating the potential for bacterial growth. For most pathogenic bacteria, pH 7 and water activity 0.99 are optimum. Growth slows as these values decrease. At pH values below 4 and at water activity values below 0.85, it is unlikely that pathogenic bacteria have grown; only a few pathogenic bacteria can grow at water activity levels below 0.92 (6). If such foods are considered vehicles, rational explanations must be sought. Challenge tests can be conducted to demonstrate growth of specific pathogens during simulated holding for varying durations at various temperatures (7).

Finding the Initial Source of the Pathogens

If it is found--or if data suggest--that a product has been contaminated before its entrance into the establishment under investigation, the investigation should be redirected to an earlier processing or production phase. This step may include a traceback of the product from a food service establishment, to a processor and/or distributors, to the farms or ranches where animals were raised or other food products were grown or harvested. At farms, investigators can sample feed, fecal droppings, and litter; make drags over litter; or test environmental conditions (e.g., water, fertilizer) in an attempt to associate the outbreak strain with a herd, flock, or plant. Success in this endeavor involves cooperation and action (along with official agreements and documentation) by state or federal departments of agriculture or by the Food and Drug Administration, as well as by the food industry. Often, however, previously collected epidemiologic, ecologic, microbial, chemical, or other scientific data, have predicted li kely pathogen sources--and perhaps modes of contamination--thus nullifying the need for traceback investigations, which are complex and expensive (Table 1).

Confirming Findings and Using the Information for Food Safety

For a variety of reasons, all elements of the approach discussed in this paper may not be possible in all outbreak investigations. Nevertheless, all available evidence should be collected to implicate a food, to clear other foods of possible involvement, and to identify contributory factors. Despite barriers to complete investigations, the etiologic agent, its sources, and contributory factors should not be just a matter of opinion [8].

Often, investigators raise more questions than they answer. If the conclusions are not plausible according to prevailing scientific knowledge, research should be initiated to resolve the differences. That is a way new knowledge is generated.

Identification of operations that have contributed to previous outbreaks does not prove that those operations occurred before the outbreak currently under investigation, but it does show conditions that could have allowed contamination, survival and/or propagation of pathogens [4,5,9-11]. Inversely, the lack of such identification does not mean that the operations--or others-- did not contribute to the outbreak. Each Outbreak should be critically reviewed before it is classified according to the various categories of surveillance data [1,12-15]. In time, data accumulate on incidence, frequency of etiologic agent, geographic distribution, place of mishandling or mistreatment, season of occurrence, frequency of vehicles, and frequency of contributory factors. Of particular importance to the sanitarian are data on places of mishandling, vehicles, and factors that contributed to the outbreaks.

Once the contributory factors have been determined, they can be used to prevent further occurrences in the place of mishandling. Sanitarians, food microbiologists, or other health department officials can stimulate development and implementation of a hazard analysis critical control point (HACCP) plan at the establishment. If practices that contributed to the outbreak are commonplace within a segment of the food industry, investigators should inform the managers of other establishments at risk about the hazards, control and preventive measures, and monitoring procedures. The information also can be used to anticipate hazards and estimate risks; guide inspections; promulgate food regulations; train public health staff, food regulatory personnel, and food workers; and educate the public. This is the way to ensure food safety.


(1.) Bryan, F.L., O.D. Cook, J.J. Guzewich, D. Maxson, R.C. Swanson, E.C.D. Todd, and L. Wisniewski (1999), Procedures to Investigate Foodborne Illness, 5th ed., Des Moines, Iowa: International Association of Milk, Food, and Environmental Sanitarians.

(2.) Murray, PR., E.J. Baron, MA. Pfaller, F.C. Tenover, and R.H. Yolken, eds. (1995), Manual of Clinical Microbiology, 6th ed., Washington, D.C.: American Society for Microbiology.

(3.) Bryan, F.L. (1996), "Hazard Analysis: The Link Between Epidemiology and Microbiology," Journal of Food Protection, 59:102-107.

(4.) Bryan, F.L. (1988), "Risks of Practices, Procedures and Processes that Lead to Outbreaks of Foodborne Diseases," Journal of Food Protection, 51:663-673.

(5.) Weingold, SE., J.K. Fudala, and, J.J. Guzewich (1994), "Use of Foodborne Disease Data for HACCP Risk Assessment," Journal of Food Protection, 57:820-830.

(6.) International Commission on Microbiological Specifications for Food (1996), Microorganisms in Foods 5, Microbiological Specifications of Food Pathogens, Toronto: University of Toronto Press.

(7.) Notermans, S., GC. Mead, P in't Veld, and T. Wijtzes (1993), "A User's Guide to Microbial Challenge Testing for Ensuring the Safety and Stability of Food Products," Food Microbiology, 10:145-157.

(8.) Salmon, R.L., T.N. Alisup, T.J. Coleman, P. Hutchins, S.R. Palmer, C.D. Ribeiro, WN. Richie, and EJA. Willis (1991), "How Is the Source of Food Poisoning Outbreaks Established? The Example of Three Consecutive Salmonella enteritidis PT4 Outbreaks Linked to Eggs," Journal of Epidemiology and Community Health 45:266-269.

(9.) Davey, G.R. (1985), "Food Poisoning in New South Wales: 1977-1984," Food Technology Australia, 37:453-456.

(10.)Roberts, D. (1982), "Factors Contributing to Outbreaks of Food Poisoning in England and Wales 1970-1979," Journal of Hygiene, 89:491-498.

(11.) Todd, E.C.D. (1983), "Factors that Contribute to Foodborne Disease in Canada, 1973-1977," Journal of Food Protection, 46:737-747.

(12.) Bryan, F.L., J.J. Guzewich, and E.C.D. Todd (1997), "Surveillance of Foodborne Disease, Part II--Summary and Presentation of Descriptive Data and Epidemiologic Patterns: Their Value and Limitations," Journal of Food Protection, 60:567-578.

(13.) Bryan, EL., J.J. Guzewich, and E.C.D. Todd (1997), "Surveillance of Foodborne Disease, Part III--Summary and Presentation of Data on Vehicles and Contributory Factors: Their Value and Limitations," Journal of Food Protection, 60:701-714.

(14.) Guzewich, J.J., F.L. Bryan, and E.C.D. Todd (1997), "Surveillance of Foodborne Disease, Part I--Purpose and Types of Surveillance Systems and Networks," Journal of Food Protection, 60:555-566.

(15.) Todd, E.C.D., EL. Bryan, and J.J. Guzewich (1997), "Surveillance of Foodborne Disease, Part IV--Dissemination and Uses of Surveillance Data," Journal of Food Protection, 60:715-723.
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Author:Bryan, Frank L.
Publication:Journal of Environmental Health
Geographic Code:1USA
Date:Jul 1, 2000
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