The definition of a foodborne illness outbreak can be generally defined as “two or more people experiencing a similar illness resulting from the ingestion of a common food.” The definition of an outbreak may be expanded to specify that the foods are epidemiologically linked to the illness. Many factors influence the decision to initiate an investigation. For example, is the affected population considered high risk for exposure or serious illness? Are illnesses associated with the immunocompromised ,e.g. a nursing home, a daycare center? Has anyone been hospitalized? What is the severity of the illness associated with agent? Are the systems typical of a foodborne illness or are their neurological symptoms involved or bloody diarrhea? Symptoms of a foodborne illness may resemble underlying medical conditions and because of the biological variability, not everyone will have the same symptoms. Most infected people will have a similar range of symptoms, but some individuals may not show any symptoms.