The prime causes of foodborne illness are bacteria, viruses and parasites. Viruses, such as hepatitis A virus, and Norwalk and Norwalk-like virus, can also cause foodborne illness. Parasites are another origin of this type of illness and include Giardia lamblia, Cyclospora cayetanenses, and Cryptosporidium parvum. These organisms can become unwelcome guests at the dinner table. They're in a wide range of foods, including meat, milk and other dairy products, spices, chocolate, seafood, and even water.
Poultry is the food most often contaminated with disease-causing organisms.
It's been estimated that 60 percent or more of raw poultry sold at retail probably carries some disease-causing bacteria. Bacteria such as Listeria monocytogenes, Vibrio vulnificus, Vibrio parahaemolyticus and Salmonella have been found in raw seafood. Oysters, clams, mussels, scallops, and cockles may be contaminated with hepatitis A virus. For example, hot or cold foods left standing too long at room temperature provide an ideal climate for bacteria to grow. Improper cooking also plays a role in foodborne illness.