Foodborne illnesses may be diagnosed by a physician during a physical examination that includes a medical history and list of medications. A physician may ask a patient questions about:

• The types and amounts of foods eaten
  
• The locations where food was consumed (e.g., at home, in a restaurant)
  
• The symptoms experienced (e.g., nausea, vomiting, diarrhea)

Certain types of bacteria and parasites that cause foodborne illness (such as Campylobacter and Salmonella) can be detected with a laboratory test. Patients may be asked to provide a stool sample to be studied under a microscope for the presence of bacteria.

Many types of foodborne infections cannot be identified during routine laboratory tests and require specialized, experimental and/or expensive tests that are not widely available. For this reason, foodborne illnesses often go undiagnosed.