Investigation of foodborne disease outbreaks
Foodborne disease outbreaks, i.e. several similar cases occurring at the same time, are not uncommon. To identify the source and prevent reoccurrence of such outbreaks, systematic clinical and laboratory investigations have to be made. The investigation and control of foodborne disease outbreaks are multidisciplinary tasks requiring skills in the areas of clinical medicine, epidemiology, laboratory medicine, food microbiology and chemistry, food safety and food control, and risk communication and management. Many outbreaks of foodborne disease are poorly investigated, if at all, because these skills are unavailable, or because a field investigator is expected to master them all single-handedly without having been fully trained.
If you have an unusually large number of people with symptoms of foodborne diseases in your community, you should follow the general steps and procedures summarised below.
Steps in investigating a foodborne disease outbreak
- Collect initial information about the number of cases and report this to the appropriate person at the nearest health facility or District Health Office.
- Develop an initial case definition (who is ill, where are they, what are their symptoms, when did they become ill). You should also record the age and gender of all people affected.
- Develop an initial questionnaire to determine if there is a common source of contamination (e.g. if everyone affected ate the same food, or food from the same place).
- Collect specimens of faeces, vomit, etc. according to the procedures laid down by the local regulatory body and send them to a health facility for transport to the nearest Laboratory of Public Health. You will need to use a sterile container for the samples and store them in an icebox. Wear gloves and wash your hands thoroughly before and after taking samples. Send the samples to the laboratory immediately.
- If you identify a particular location or event as the origin of the outbreak you should visit the exposure site for a field inspection and environmental sampling.
- Take samples of the foods under investigation according to the procedures laid down by the local regulatory body. You will need to use sterile bags or containers and ensure that your sample is representative of the food consumed. You may need to act quickly to obtain food samples in case any remainder has been used up or disposed of.
- If the source of the outbreak is a workplace, you will need to interview the employers and employees. You should try to find out how many of them ate the same food, when they ate it, how much they ate, and where the food came from.
- Data analysis and interpretation. For example, does the data you have recorded indicate that any particular age group or gender is affected more than others?
- Report. Summarise the findings from your investigation and compile into a brief report that should be submitted to the health facility or public health emergency management centre.