Foodborne Illness Outbreak Investigation 101

Have you ever wondered how foodborne illness outbreaks are investigated?

United States has public health infrastructure that includes governmental agencies such as CDC (Center for Disease Control and Prevention), FDA (Food and Drug Administration), FSIS (Food Safety Inspection Services) and State Health Departments.

Outbreak by definition involves 2 plus individuals and typically involves large groups of people. Investigating the outbreak is a complex process and involves extensive resources.

Investigation starts at the state level where State Health Departments detect and investigate local outbreaks. The process starts with collecting information and inspecting local food establishments that could be potential sources of foodborne illness outbreaks. Results of investigations are reported to CDC.

One of the most common hazards that causes foodborne outbreaks is Salmonella. This pathogen makes approximately 1.3 million people sick and causes on average 450 deaths in the US every year. This number is an estimate as for every reported illness there are 30 more that are not reported to authorities.

Here is how investigation process looks like in steps.

  1. Outbreak detection – There are over 80 participating laboratories that conduct DNA testing to determine the common source of the microorganism. Reporting to CDC takes about 25 days from the time when patients ate adulterated food.
  2. Generating hypothesis about the sources of an outbreak. Factors taken under consideration include the following: sex, age, geographics, history of pathogens, food exposures, consumers habits, and shelf life of the product.
  3. Generating the lines of evidence used to link outbreaks to food source. This includes the following elements:
  4. epidemiologic evidence – interviewing people involved in the outbreak about their eating habits, locations, and the food they recently ate. This also includes interviewing food establishments that were mentioned during the initial interviews.
  5. Traceback evidence – This involves collecting product names, invoices, traceability information about potential food.
  6. Laboratory evidence – sampling and testing of leftover food to see if bacteria matching the DNA can be found and swabbing of food preparation environment.
  7. Interpretation of lines of evidence– linking food to a company is a long process. There must be at least 2 out of 3 lines of evidence to make the link.
  8. Pinpointing the cause
  9. Taking actions to prevent more illnesses – consumer warnings, product recalls.

CDC builds the evidence for regulatory agencies that take preventive actions.

  1. Confirming the outbreak is over – CDC closes the outbreak where illnesses stop or when the source was mitigated. Once the outbreak is closed it is reported to National Outbreak Reporting System (NORS).

Companies have regulatory responsibilities to produce and serve safe food. Compliance can be achieved by continuous education and improvements of food safety systems and practices. There are number of certificate trainings that are useful in development and improvement of food safety systems. These are HACCP, PCQI or Internal Auditor. Foodborne illnesses can be prevented with Good Manufacturing Practices and robust food safety systems. Visit our website at to learn more about training programs that are relevant to your food business.