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Foodborne disease: A disease caused by consuming contaminated food or drink. Myriad microbes and toxic substances can contaminate foods. There are more then 250 known foodborne diseases. The majority are infectious and are caused by bacteria, viruses, and parasites. Other foodborne diseases are essentially poisonings caused by toxins, chemicals contaminating the food. All foodborne microbes and toxins enter the body through the gastrointestinal tract and often causes the first symptoms there. Nausea, vomiting, abdominal cramps and diarrhea are frequent in foodborne diseases.

Many microbes can spread in more than one way, so it may not be immediately evident that a disease is foodborne. The distinction matters, because public health authorities need to know how a particular disease is spreading to take the appropriate steps to stop it. For example, infections with Escherichia coli O157:H7 (E. coli O157:H7) can be acquired through contaminated food, contaminated drinking water, contaminated swimming water, and from toddler to toddler at a day care center. Depending on which means of spread cause a case, the measures to stop other cases from occurring could range from removing contaminated food from stores, chlorinating a swimming pool, or closing a child day care center.

The most common foodborne infections are caused by three bacteria -- Campylobacter, Salmonella, and E. coli O157:H7 -- and by a group of viruses called calicivirus, better known as Norwalk-like virus:

Campylobacter -- Campylobacter is the most common bacterial cause of diarrheal illness in the world. The bacteria live in the intestines of healthy birds, and most raw poultry meat has Campylobacter on it. Eating undercooked chicken, or other food that has been contaminated with juices dripping from raw chicken is the most frequent source of this infection. Aside from diarrhea, common symptoms include causes fever, diarrhea, and abdominal cramps. Salmonella -- Salmonella is widespread in the intestines of birds, reptiles and mammals. People can acquire the bacteria via a variety of different foods of animal origin. The illness it causes is called salmonellosis and typically includes fever, diarrhea and abdominal cramps. In persons with poor underlying health or weakened immune systems, Salmonella can invade the bloodstream and cause life-threatening infections. E. coli O157:H7 -- E. coli O157:H7 has a reservoir in cattle and other similar animals. Illness typically follows consumption of food or water that has been contaminated with microscopic amounts of cow feces. The illness it causes is often a severe and bloody diarrhea and painful abdominal cramps, without much fever. But in 3 to 5% of cases, a lifethreatening complication called the hemolytic uremic syndrome (HUS) can occur several weeks after the initial symptoms, resulting in anemia, profuse bleeding, and kidney failure. Calcivirus (Norwalk-like virus) -- Calicivirus (Norwalk-like virus) is an extremely common cause of foodborne illness (though it is rarely diagnosed, because the laboratory test is not widely available). It causes an acute gastrointestinal illness, usually with more vomiting than diarrhea, that resolves within two days. Unlike many foodborne pathogens that have animal reservoirs, it is believed that Norwalk-like viruses spread primarily from one infected person to another. Infected kitchen workers can contaminate a salad or sandwich as they prepare it, if they have the virus on their hands. Infected fishermen have contaminated oysters as they harvested them.

Common diseases that are usually transmitted by other routes are occasionally foodborne. These include infections caused by Shigella, hepatitis A, and the parasites Giardia lamblia and Cryptosporidia. Even strep may be occasionally transmitted through food.

Food toxins -- Some foodborne diseases are caused by a toxin in the food that was produced by a microbe in the food. For example, staph bacteria (Staphylococcus aureus) can grow in food and produce a toxin that causes intense vomiting. The rare but deadly disease botulism occurs when the bacterium Clostridium botulinum grows and produces a powerful paralytic toxin in foods. These toxins can produce illness even if the microbes that produced them are no longer there.

Other foodborne diseases -- Among the many other foodborne diseases are the following: amebiasis (Entamoeba histolytica infection), Blastocystis hominis infection, bovine spongiform encephalopathy (BSE) and Creutzfeldt-Jakob disease (CJD), cholera, cryptosporidiosis (crypto), cyclospora cayetanensis, diarrheagenic Escherichia coli (E. coli), viral gastroenteritis, giardiasis, listeriosis, marine toxins shigellosis, travelers' diarrhea, trichinosis (trichinellosis), typhoid, Vibrio parahaemolyticus and Vibrio vulnificus infection.

Magnitude of the problem -- An estimated 76 million cases of foodborne disease occur each year in the US alone. The great majority of these cases are mild and cause symptoms for only a day or two. Some cases are more serious, and CDC estimates that there are 325,000 hospitalizations and 5,000 deaths related to foodborne diseases each year in the US. The most severe cases tend to occur in the very old, the very young, those who have an illness already that reduces their immune system function, and in healthy people exposed to a very high dose of an organism.

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