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San Francisco Health Network
Environmental Health

Food Safety Program - Foodborne Illness Investigations

Environmental Health may investigate foodborne illness complaints when three (3) people or less are ill. If the illness affects four (4) or more persons, call Disease Control at (415) 554-2830.


Investigation Procedure

After Communicable Disease Control reports a foodborne lllness to the Environmental Health Section, the foodborne illness investigation program aims to:

  1. Identify cases associated with an incident
  2. Detect implicated foods
  3. Elucidate information about causative agents and their sources
  4. Determine the factors that contribute to contamination, growth and survival of etiologic agents.


If the responsible food can be identified, further cases may often be prevented by:

  1. Halting its distribution and sale
  2. Recalling production lots already distributed, and
  3. Implementing impound, reprocessing, or disposal of the contaminated foods to prevent their entry or reentry into food channels.


Rapid identification of the agent may lead to specific treatment of victims. Future outbreaks can be prevented by explaining the problem to food service operators to avoid recurrences. As epidemiological point's data accumulates, information will indicate the critical control point in food production, processing, and preparation and appropriate methods for controlling and preventing foodborne disease.


An outbreak investigation involves getting notification of illnesses which might be foodborne, interviewing the ill and the persons at risk but who remained well, making epidemiological associations from initial information, and forming hypotheses. Based upon those hypotheses, additional actions must follow. This includes collecting specimens and samples and visiting the place(s) where suspected foods were produced, processed, or prepared (if out of county, the appropriate county lead agency would be notified and efforts would then be coordinated) to determine sources and models of contamination, survival or growth of the causative agent.


The public relies on health inspectors for protection from foodborne illness. Such protection depends on rapid detection of outbreaks and a thorough knowledge of the agents and factors responsible for foodborne illness. Within days of processing, current food distribution systems are able to circulate contaminated products throughout a country or even to other countries. Local investigations of reported foodborne illness can, therefore, influence national and international foodborne disease surveillance and control.