Illness characterised by vomiting, diarrhoea and abdominal pain, resulting from eating food contaminated with metallic or chemical poisons, certain micro-organisms or microbial products. Some foods, such as undercooked red kidney beans or fish of the scombroid family (mackerel and tuna), may sometimes contain natural poisons. Food poisoning caused by chemical or metallic substances usually occurs rapidly, within minutes or a few hours of eating. Among micro-organisms, bacteria are the leading cause of food poisoning, particularly Campylobacter jejuni, Staphylococcus aureus, Clostridium perfringens, Salmonella, and Escherichia coli O157.

Enteritis caused by Campylobacter jejuni is the commonest reported cause of food poisoning in the UK with over 70,000 notifications yearly to public health services (likely to be the tip of an iceberg, however). People usually recover within 1–3 days but a few will have more serious disease. The most frequent cause is from contaminated poultry.

Staphylococcal food poisoning occurs after food such as meat products, cold meats, milk, custard and egg products becomes contaminated before or after cooking, usually after unhygienic handling by humans who carry S. aureus. The bacteria produce an ENTEROTOXIN which causes the symptoms of food poisoning 1–8 hours after ingestion. The toxin can withstand heat so cooking of contaminated food does not prevent illness.

Heat-resistant strains of Cl. perfringens cause food poisoning associated with meat dishes, soups or gravy when dishes cooked in bulk are left unrefrigerated for long periods before consumption. The bacteria are ANAEROBES and form spores; spores multiply rapidly during cooling, resulting in heavy contamination. Once eaten, the bacteria produce enterotoxins in the intestine, causing symptoms within 8–24 hours.

Many different types of Salmonella cause food poisoning or ENTERITIS, from eight hours to three days after ingestion of food in which they have multiplied. Salmonella infections are common in animals such as cows, pigs and poultry whose meat and milk may be infected, although the animals may show no symptoms. Duck eggs may harbour Salmonella (usually S. typhimurium), arising from surface contamination with the bird's faeces, and foods containing uncooked or lightly cooked hen's eggs, such as mayonnaise, have been associated with enteritis. Although Salmonella are mostly killed by heating at 60 °C for 15 minutes, contaminated food requires considerably longer cooking and, if frozen, must be completely thawed beforehand, to allow even cooking at a sufficient temperature.

E. coli O157 was reported in 800 cases in England & Wales in 2014. The illness can be severe, with bloody diarrhoea and life-threatening renal complications (see HAEMOLYTIC URAEMIC SYNDROME). The reservoir for this pathogen is thought to be cattle, and transmission results from consumption of raw or undercooked meat products and of raw dairy products. Cross-infection of cooked meets by storing them adjacent to raw meat is a common cause of outbreaks of Escherichia coli O157 food poisoning. Water and other foods can be contaminated by manure from cattle, and person-to-person spread can occur, especially in children, so careful hand-washing is important after handling farm animals.

Food poisoning associated with fried or boiled rice is caused by Bacillus cereus, whose heat-resistant spores survive cooking. An enterotoxin is responsible for the symptoms, which occur 2–8 hours after ingestion and resolve after 8–24 hours.

Viruses are emerging as an increasing cause of some outbreaks of food poisoning from shellfish (cockles, mussels and oysters).