INVESTIGATE THE INCIDENCE OF FOOD BORNE DISEASE OUTBREAK

1.      INTRODUCTION

Food-borne illness results from the natural, accidental, or malicious contamination of foods by microbiological or chemical substances. The impacts of food-borne illness may include morbidity and mortality, increased health care costs, loss of consumer confidence, economic losses, and lost productivity to industry.

Changes in food distribution networks and the increased globalization of trade in food have resulted in larger volumes of raw and processed products moving across domestic and international boundaries.

Consequently, food-borne illness outbreaks associated with widely distributed foods result in human illnesses that cross local, provincial/territorial and international boundaries.

Regulatory bodies responsible for human health and food safety respond to these events through the development of enhanced food-borne illness surveillance networks, including the use of molecular sub typing and other laboratory technology, to enable cluster detection and the linkage of seemingly unrelated cases to initiate outbreak investigation.

Increased concern and public awareness of food safety has heightened the demand for swift resolution of food safety issues at a time when they are becoming increasingly complex, reinforcing the need for collaboration in multi-jurisdictional outbreak investigations and the active participation of all partners in centrally led efforts to mitigate risk and prevent further illness.

2.      PURPOSE OF THE INVESTIGATION

There are many reasons to do an outbreak investigation. Those reasons can be listed as,

·         Control and prevention

The primary reason to investigate an outbreak is to control the occurrence of disease and prevent further disease. Therefore, it is necessary to first determine whether the outbreak is ongoing or is over. If the outbreak is ongoing, the first goal should be to prevent new cases. If the outbreak has already occurred, the goal should be to determine the factors or sources that contributed to the outbreak and prevent them from occurring in the future.

·         Surveillance

Outbreak investigations can add valuable information to ongoing public health surveillance activities. The goal of surveillance is not to compile numbers of cases of illness for administrative purposes, but to provide data that are important to guide public health policy and action. Continual surveillance adds to existing knowledge regarding the potential for and occurrence of a disease in a population.

·         Research opportunities

An important objective of an outbreak investigation is to gain additional knowledge regarding the natural history of the disease. Carefully conducted investigations may reveal trends, new or overlooked disease agents, novel vehicles or transmission modes, groups at risk or specific risk factors. New knowledge may also be gained by assessing the impact and effectiveness of control measures.

·         Administrative concerns

Identifying the cause of outbreaks may be used to evaluate and improve current health programs in the community, identify high-risk groups or etiologic agents previously overlooked and guide future strategies and future allocations in these areas.

·         Political or legal concerns

There may be overwhelming pressures placed on the local health departments (LHD) by families of affected individuals, the media, local politicians and others to determine the source of an outbreak and whether it may pose a continued or future threat to the community.

3.      STEPS INVOLVE IN INVESTIGATING AN OUTBREAK

Prompt response to food related complaints is the foundation of a successful investigation. Important steps and information necessary to determine the initiation and extent of an investigation include examination of test results and preliminary evidence such as onset times, symptoms and duration of illness, development of hypotheses, assessment of the magnitude of the problem, and evaluation of available resources.

The procedure for the investigation and determination of the existence of an outbreak is reasonably standard regardless of the disease being investigated. The steps involve in investigation is listed below and they are not sequential and some contingency planning can be done before an outbreak. The steps in this procedure include;

• preparation for a detailed epidemiologic investigation
• establish the existence of an outbreak or epidemic
• verify diagnosis
• formulate a tentative hypothesis
• put control measures into operation
• conduct the investigation
• relate the outbreak to time, place and person
• analyze and interpret data
• test hypothesis and formulate conclusions
• prepare a final report of the investigation

3.1             Preparation for a detailed epidemiologic investigation

Planning an epidemiologic investigation may be considered as the initial step in the process because part of the planning can be done before an outbreak occurs. The responsible department can begin by training personnel in how to compile line lists, develop questionnaires, conduct interviews, and use epidemiologic information.

The department should have 6-8 stool culture kits on hand or readily available should an outbreak occur because in most cases stool specimens must be collected within 72 hours of onset of illness to isolate and identify certain pathogens (e.g., Clostridium perfringens, Bacillus cereus, and Staphylococcus aureus).

Lists of contacts such as administrative contacts, additional personnel, sanitarians, regional contacts, physicians, clinical laboratories, or other persons who may become involved in outbreak investigations should be assembled.

Resource materials describing signs and symptoms, incubation times and specifics regarding specimen collection and appropriate kits to be used should be maintained and readily available to those processing the initial calls. This may help in formulating an initial hypothesis.

Once the investigation is underway, the proper clinical specimens should be collected as soon as possible before patients recover and become less likely to submit specimens, and before the general interest in the investigation wanes.

All suspected food borne outbreaks should be examined and a determination made regarding the feasibility of conducting an investigation even if the time to collect proper clinical specimens has passed. This is done in order to determine the source of the outbreak and to prevent similar outbreaks from recurring.

3.2             Establish the existence of an outbreak or epidemic

Establish the existence of an outbreak by comparing the incidence of the disease in a specified population during a comparable previous time period or when point source outbreaks occur in order to be familiar with disease trends in the community and determine whether there actually is a higher than expected number of cases in a community.

This can be done through diligent public health surveillance that provides an accurate assessment of the status of the health of the community and helps to determine any increases or decreases in communicable diseases in the local population.

Surveillance data should be reviewed by the responsible department on a regular basis to become familiar with the status of all communicable diseases in the area of jurisdiction.

While establishing the existence of an outbreak, have to be aware of artificial causes of increases such as;

• changes in local reporting,
• changes in case definitions of reportable diseases,
• increased local or national interest in particular diseases,
• new physicians in the area,
• new diagnostic procedures which might identify new or existing infectious agents, and
• Increased populations or new arrivals into the area.

3.3             Verify diagnosis

Analyze clinical histories of cases and have laboratory tests performed in order to confirm the etiologic agent associated with the illness. Clinical, laboratory and epidemiologic evidence should be considered.

Verify that laboratory results are consistent with the clinical evidence as laboratory errors sometimes occur. In verifying the diagnosis, it is crucial to collect clinical and environmental samples as soon as possible because many etiologic agents become more difficult to isolate with time (e.g., Bacillus cereus, Clostridium perfringens, Staphylococcus aureus).

As case-patients begin to recover they may become more reluctant to submit clinical samples. Also, when delay occurs, environmental samples are more likely to be discarded or disinfected.

3.4             Formulate a tentative hypothesis

Formulate a tentative hypothesis to explain the most likely cause of illness, etiologic agent, vehicle, and distribution of cases. Hypothesis generating is an ongoing process. It may begin with the first phone call.

This hypothesis may be based on known incubation periods, symptoms, duration of illness or foods eaten, as well as knowledge about the various agents responsible for outbreaks. The tentative hypothesis directs the course of an investigation and control measures, and is tested by data gathered during the investigation.

A series of hypotheses may evolve during an investigation. First, facts are examined and broad hypotheses are formulated. As more facts are gathered, a more specific hypothesis may be formulated.

Confirm the diagnosis if laboratory testing has been completed.

Examine case histories to determine if there are common exposures, or if signs and symptoms and onset of illness are consistent with etiologic agents. Next, additional facts to test the new hypothesis are gathered. The cycle is continued as necessary.

3.5             Put control measures into operation

The priority during each investigation should be to implement effective control measures.

This should be done early in the course of the investigation based on the initial hypotheses. Factors to consider when determining the most effective control measures include the extent of the illness, who was affected, when and where did the critical exposure take place, what was the vehicle, how was the disease transmitted, what is the etiologic agent and whether or not there is a potential for ongoing or future transmission.

Control measures should focus on specific agents, sources, or reservoirs of infection and should be targeted to interrupt the transmission of disease or reduce exposure to disease. These measures should be instituted as soon as possible to control the current problem and demonstrate to the community that efforts are being made to control the problem.

Use the information collected during the investigation to control the current situation and to prevent future problems in the community.

3.6             Conduct the investigation

Conducting the investigation can be listed as;

• Prepare a line list of ill persons listing signs, symptoms, onset times, duration of illness.
• Gather appropriate community and environmental information; investigate potential sources of the responsible agent and factors that may have contributed to the outbreak.
• Obtain clinical specimens (usually stool specimens) from ill case patients for laboratory analysis of enteric pathogens.
• When possible, obtain samples of implicated food or environmental samples for laboratory analysis. Hold these samples under refrigeration until a known etiologic agent has been identified.

3.7             Relate the outbreak to time, place and person

If an outbreak occurs following a common meal or exposure (e.g., wedding, parties), conduct a survey of known cases to investigate commonalties, such as onset of illness (time), population characteristics (e.g., age, gender) (person) and where they could have been infected or exposed (place).

If an outbreak does not have an established common meal or exposure (e.g., an increase of cases of illness in a community within a close time frame), it may be necessary to start with an informational or a more general survey in order to select case patients.

Develop a questionnaire and perform a case-control study or cohort study. It is imperative to interview non-ill (control) persons who are similar or had similar experiences regarding time and place to those ill. Begin by interviewing and analyzing data from 20-25 ill persons (if available) and 20-25 well persons who had the same exposures but remained well.

Obtain identifying information (name, address, telephone number, etc.); demographic information (age, sex, race, occupation or group characteristics); and clinical information (symptoms, onset times, and duration of illness).

Establish a Case Definition

Begin with broad or “loose” definitions that may be narrowed as more cases are defined. Classify cases as “lab-confirmed” or “probable”. Not all cases need to be lab-confirmed. Make case counts and relate these to the appropriate population to determine those groups at risk (e.g., same age groups, same sex, and occupation).

Develop a line listing of cases. Contact those with information on the illness or environmental circumstances contributing to the outbreak (e.g., physicians, sanitarians). When attempting to identify cases, additional contacts may need to be surveyed such as physicians, clinics, hospitals, laboratories and friends of case-patients.

In some situations the media may be used to solicit case-patients, but this approach should be considered carefully to avoid biasing an epidemiologic investigation and damaging the reputation of local establishments unnecessarily.

3.8             Analyze and interpret data

Summarize field investigations. Compare and interpret all information collected and results of tests conducted. Construct epidemic curves to detect the course of the outbreak and to determine if the illness originated from a single source or is on going, calculate attack rates, develop appropriate tables and charts, apply statistical tests and interpret the cumulative data. Define the geographic extent of the outbreak and the population at risk.

3.9             Test hypothesis and formulate conclusions

Accept or reject the hypothesis on the basis of the available data and appropriate statistical analysis. For a hypothesis to be accepted, the patterns of disease must fit the nature of the agent, its source, its mode of transmission, and the contributory factors that allowed the outbreak to occur.

If the hypothesis is rejected, another hypothesis should be developed and additional data gathered in order to test this new hypothesis. A more systematic study can be conducted as needed to improve the sensitivity and specificity of the findings, establish the true number of cases, and assist in arriving at more definitive conclusions.

3.10         Prepare a final report of the investigation

Investigations should be summarized as soon as completed and a final report sent to the responsible department / authority. These final reports serve as a record of the rationale and provide documentation for the activities conducted during the investigation.

The final report can also be used to improve future investigations and prevention measures. The report should follow the usual scientific format of introduction, background, methods, results, discussion, references and recommendations.

Do not use the names of case-patients. The names of responsible department personnel or authorized personnel involved in the investigation may be included. The names of facilities or locations where the food borne outbreak occurred may be included.

The background is a short paragraph describing why the outbreak investigation was initiated and may include who was affected, how many people were ill and how many exposed, where the outbreak occurred, the severity and clinical presentation of the cases. Note whether or not the outbreak involved a particular setting or social event (e.g., school, restaurant, wedding, festival) or to particular population (e.g., nursing home, day care center).

The methods section should list how cases were identified, how questionnaires were developed, methods used to collect data, as well as clinical and environmental samples, laboratory tests performed, statistical methods, control methods instituted, and other features of the investigations used during the outbreak investigation.

The results section should list what was discovered in the investigation, results of laboratory testing of clinical or environmental samples, results of the epidemiologic investigation, the sanitarian’s report, statistical results, epi-curves, tables, charts and other studies used during the investigation.

The discussion should briefly summarize the findings of the investigation. Evaluate the control and methods used in the investigation. Were they successful? Could they be instituted in similar outbreaks in the future or how should they be changed? What problems were encountered ? Is the current surveillance program sufficient to identify and control future outbreaks? , etc.

List any important or unique aspects of the outbreak or a specific disease agent uncovered during the investigation.

4.      SUMMARY

Food borne outbreaks have to be investigated for prevention of further occurring as well as for future requirements. About 10 steps can be used to investigate an outbreak as described above. Those steps can be carried out in an order or change of order or skip of steps according to the nature of food borne outbreak and requirement in investigation.

5.      REFERENCES

• Food borne disease outbreaks by Washington State Department of Health, Last Revised on January 2013
• Investigating Food borne Disease Outbreaks by Andrea Ellis
• Guidelines for Food borne Disease Outbreak Response by CIFOR (council to improve foodborne outbreak response)
• FOODBORNE AND WATERBORNE DISEASE OUTBREAK INVESTIGATION MANUAL by Department of Health and Family Services, Wisconsin Division of Public Health, Bureau of Communicable Diseases, Communicable Disease Epidemiology Section.
•  Guidelines for Investigating Foodborne Illness Outbreaks by Rhode Island Department of Health
• FOODBORNE ILLNESS AND OUTBREAK INVESTIGATION MANUAL by Kansas Department of Health and Environment, Division of Health
• General Outbreak Investigation / Notification Protocol by West Virginia Department of Health and Human Resources, January 2008
• FOOD BORNE DISEASE OUTBREAKS : guidelines for investigation and control by world health organization (WHO)
•  http://doh.dc.gov/service/foodborne-disease-outbreaks
• http://www.phac-aspc.gc.ca/zoono/fiorp-mitioa/index-eng.php
• http://labspace.open.ac.uk/mod/oucontent/view.php?id=451997&section=1.8