Food infection occurs when a pathogen enters the gastrointestinal tract and multiplies. Microorganisms can penetrate into the intestinal mucosa and grow there, or they can pass through other systemic organs. Infections are characterized by a delay in the appearance of gastrointestinal disturbance while the pathogen increases in numbers or affects invaded tissue. There is also usually a fever, one of the body's general responses to an infective organism.

Food borne infections remain a major public health problem. The Council for Agricultural Science and Technology estimated in its 1994 report, Food borne Pathogens: Risks and Consequences that as many as 9,000 deaths and 6.5 to 33 million illnesses in the United States each year are food-related.