The causes for food poisoning can be bacterial or viral agents. Common bacterial agents are Salmonella species, Shigella species, Escherichae coli, Bacillus cerues, Campylobacter species and staphylococcal aureus.
Some bacteria cause the symptoms of gastroenteritis by releasing toxins. These toxins are heat resistant and can not be destroyed by reheating ( such as frying). Other bacterial toxins cause symptoms by directly invading and causing damage to the gut wall.
Viral gastroenteritis is estimated to be responsible for 25% to 40% of hospital admissions for diarrhoeal illness. Viruses are easily transmitted through water and contaminated and improperly cooked seafood such as clams, oysters. Hepatitis A can present as food poisoning during the early stages of the disease (see related article on hepatitis A on this website).