The most commonly recognized food borne infections are those caused by the bacteria Campylobacter, Salmonella, and E. coli O157:H7, and by a group of viruses called calicivirus, also known as the Norwalk and Norwalk-like viruses.
Food borne microbes can be introduced from infected humans who handle the food, or by cross contamination from some other raw agricultural product. For example, Shigella bacteria, hepatitis A virus and Norwalk virus can be introduced by the unwashed hands of food handlers who are themselves infected.