More than 250 foodborne illnesses have been identified. Most of them are infections, caused by pathogens (organisms that cause disease) such as bacteria, viruses and parasites found in food. Others are poisonings caused by toxins or chemicals that have contaminated food, such as food served in lead-glazed pottery, or naturally poisonous foods, such as poisonous mushrooms.

The most common types of foodborne illnesses include:

• Campylobacteriosis. Caused by the Campylobacter bacteria, which is the most commonly identified bacteria that causes diarrhea. The bacteria live in the intestines of birds. Undercooked chicken or other foods are frequent sources of this type of infection.
  
  
• Clostridium perfringens infection. Results in diarrhea, abdominal pain, nausea and vomiting and usually develops after eating improperly stored or cooked meat.
  
  
• Salmonellosis. Caused by the Salmonella bacteria, which is widespread in the intestines of birds, reptiles and mammals. Any type of food can become contaminated with the salmonella bacteria. The foods that most frequently transmit salmonella are poultry, meat, eggs and dairy products. People may also be exposed to salmonella through contact with household pets - especially lizards, turtles, and snakes - and through contact with contaminated surfaces, such as computer keyboards and cooking utensils. Fever, diarrhea and abdominal cramps are common symptoms. In people with poor health or weakened immune systems, bacteria can enter the bloodstream and cause life-threatening infections. Some infected people do not develop symptoms, but instead become carriers and spread the infection to others.
  
  
• Escherichia coli (E. coli) infection. E. coli is a bacterial pathogen found in cattle and other related animals. Illness often occurs when people consume food (especially beef) or water that has been contaminated with microscopic amounts of cow feces. E. coli can also be spread through contact with contaminated surfaces and by touching infected animals (e.g., petting zoos). The illness causes severe diarrhea that may be bloody and painful abdominal cramps. In a small number of cases, a serious condition called hemolytic uremic syndrome (HUS) can occur. This can result in anemia, profuse bleeding and kidney failure.
  
  
• Calicivirus. An extremely common cause of viral foodborne illness. However, this type is rarely diagnosed because the laboratory test is not widely available. The virus (a type of norovirus) can spread from one person to another or through food.  For instance, a kitchen worker may spread the virus during food preparation.
  
  
• Shigellosis. Caused by the Shigella bacteria. It can be transmitted by eating food or drinking beverages contaminated by food handlers with Shigella, eating vegetables grown in fields containing sewage, eating food contaminated by flies bred in infected feces and drinking or swimming in contaminated water. The bacteria cause fever, bloody diarrhea and abdominal pain.
  
  
• Bacillus cereus food poisoning. Caused by the Bacillus cereus bacteria. It usually presents with extreme nausea and vomiting and has the fastest onset of symptoms (three hours) of foodborne illnesses. Bacillus cereus food poisoning is commonly seen in people after consuming Chinese fried rice.
  
  
• Staphylococcal food poisoning. Caused by the Staphylococcus aureus bacteria. Unlike other types of foodborne illness, this form is not caused by contamination. The bacteria can grow in some foods (e.g. dairy products, fish and processed meats) and produce a toxin that results in intense vomiting.
  
  
• Ascariasis (roundworm). A parasitic worm infection caused by contact with contaminated food or soil.
  
  
• Vibrio. There are many different types of this bacteria, one of which causes cholera. Other Vibrio species are commonly found in raw or undercooked shellfish. An infection often causes chills and fever.
  
  
• Giardiasis. Caused by the parasite Giardia that is passed to humans in drinking water or from infected animal products. Giardia is a common traveler’s illness which causes abdominal cramps and diarrhea.
  
  
• Chemical food poisoning. Some types of foods, such as certain species of mushrooms, contain toxins that result in illness. Most cases result in mild symptoms. However, some are more serious and require immediate medical treatment.
  
  
• Botulism. A rare, but serious illness caused by the Clostridium botulinum bacteria. If untreated, it can cause paralysis and respiratory failure. Cases of botulism are usually contracted from insufficiently heated home-canned foods, such as asparagus, green beans, beets and corn.