All foods naturally contain small amounts of bacteria.
But when food is poorly handled, improperly cooked or inadequately stored, bacteria can multiply in great enough numbers to cause illness. Parasites, viruses and chemicals can also contaminate food. Foodborne illness from these sources, however, is less common. Signs and symptoms of food poisoning vary with the source of contamination. Generally diarrhea, nausea, abdominal pain and sometimes vomiting occur within hours of eating contaminated food.