Food poisoning is illness that results from eating food that is contaminated by microorganisms or chemicals, or that is poisonous in itself. Food can be contaminated by such chemicals as lead or zinc, leading to food poisoning. Several varieties of mushrooms and certain species of fish are poisonous if eaten. More often, food poisoning is caused by microorganisms, such as bacteria, molds, viruses, and parasites.
Some food-poisoning agents are already in food at the time the game or livestock is killed or the plants are harvested. Many microorganisms cause food to spoil but are otherwise harmless. Certain bacteria that grow in food, however, produce toxins (poisons) that cause illness. The bacterium Staphylococcus << `staf` uh luh KOK uhs >> produces toxins that cause vomiting and diarrhea a few hours after the contaminated food is eaten. The bacterium Clostridium botulinum << klos TRIHD ee uhm BOCH uh lihn uhm >> causes a far more serious, often fatal, type of food poisoning called botulism.
Many instances of food poisoning are really infections by bacteria, viruses, or parasites that multiply in the body and cause illness. The most common foodborne bacteria are Salmonella and Campylobacter << `KAM` pih loh BAK tuhr >>. These bacteria affect the stomach and intestines, causing nausea and diarrhea. A variety of the common bacterium Escherichia coli << ehsh uh RIHK ee uh KOH ly >> called E. coli O157:H7 causes severe illness and kidney failure, particularly in children. The virus that causes hepatitis A, a serious liver disease, is often transmitted to people through contaminated food or water. Disease-causing parasites, such as Cryptosporidium << krihp toh spaw RIHD ee uhm >> and Giardia << jeh AHR dee uh >>, often contaminate uncooked vegetables. 
Food-poisoning illnesses are usually brief and mild, and cause no permanent harm in healthy people. The elderly, the very young, pregnant women, and people whose immune systems are weakened by illness or medication are most susceptible to food poisoning.
Proper processing and preparation of food destroy most food-poisoning agents and prevent most illness. Food preparers should wash their hands often and not work if they are ill. People should always thoroughly wash foods before eating them, especially if the food is eaten raw. Refrigerating, freezing, or holding cooked foods at temperatures too high for bacteria to grow are also important for keeping foods safe.
