<P> The vast majority of reported cases of foodborne illness occur as individual or sporadic cases . The origin of most sporadic cases is undetermined . In the United States, where people eat outside the home frequently, 58% of cases originate from commercial food facilities (2004 FoodNet data). An outbreak is defined as occurring when two or more people experience similar illness after consuming food from a common source . </P> <P> Often, a combination of events contributes to an outbreak, for example, food might be left at room temperature for many hours, allowing bacteria to multiply which is compounded by inadequate cooking which results in a failure to kill the dangerously elevated bacterial levels . </P> <P> Outbreaks are usually identified when those affected know each other . However, more and more, outbreaks are identified by public health staff from unexpected increases in laboratory results for certain strains of bacteria . Outbreak detection and investigation in the United States is primarily handled by local health jurisdictions and is inconsistent from district to district . It is estimated that 1--2% of outbreaks are detected . </P> <P> In postwar Aberdeen (1964) a large - scale (> 400 cases) outbreak of typhoid occurred, caused by contaminated corned beef which had been imported from Argentina . The corned beef was placed in cans and because the cooling plant had failed, cold river water from the Plate estuary was used to cool the cans . One of the cans had a defect and the meat inside was contaminated . This meat was then sliced using a meat slicer in a shop in Aberdeen, and a lack of cleaning the machinery led to spreading the contamination to other meats cut in the slicer . These meats were then eaten by the people of Aberdeen who then became ill . </P>

Which bacteria is the most common source of food borne illness