Foodborne illnesses (commonly known as food poisoning) are gastrointestinal infections that occur when foods contaminated with harmful organisms are ingested.

Food can be contaminated by a number of pathogens (organisms that cause disease) including bacteria, viruses and parasites. The pathogen enters the body by the mouth and then travels into the stomach and intestines. After infection, an incubation period occurs, which may last from hours to days before symptoms appear.

Although rarer, foodborne illness can also be caused by toxins and chemicals. For instance, pesticides can remain on foods, which can cause illness. A naturally toxic substance, such as poisonous mushrooms, may be consumed, also causing sickness. Symptoms vary according to the source and may include nausea, vomiting, abdominal cramps and diarrhea.

The risk of acquiring foodborne illnesses is typically greater during the summer months because the warm weather speeds up bacterial growth on raw meats and poultry.

In most cases, foodborne illnesses are not serious and do not cause serious complications. However, certain types of illnesses such as botulism (severe food poisoning caused by a bacterial toxin) can result in serious health consequences (such as spontaneous abortion in pregnant women) or death.

In some people (especially children) a condition called hemolytic uremic syndrome (HUS) can result from infection by a particular strain of the E. coli bacteria. HUS is a rare disorder that usually affects children between ages 1 to 10. Although most children recover completely, it may cause acute renal (kidney) failure, seizures, heart failure, pancreatitis or, in rarer cases, diabetes.

The types of common foodborne illnesses can change over time. Typhoid fever, tuberculosis and cholera were once common foodborne diseases before food safety measures (such as pasteurization and safe food canning) became commonplace. In recent years, new foodborne illnesses have been discovered. In 1996, the parasite Cyclospora was identified as a cause of diarrhea that occurred after Guatemalan raspberries were consumed. In 1998, a new strain of the bacteria Vibrio parahaemolyticus contaminated oyster beds in Galveston Bay, Texas, and caused people that consumed the oysters to become ill.

Although local and state health departments are required to report cases of foodborne illness to the U.S. Centers for Disease Control and Prevention (CDC), establishing precise figures is difficult.  Most cases are not diagnosed because people do not seek treatment for the illness or physicians do not diagnose it. Therefore, the case is never reported to the CDC.

According to estimates by the CDC, there are approximately 76 million cases of foodborne illness each year in the United States. These cases result in an estimated 325,000 hospitalizations and 5,000 deaths annually.

In addition to tracking individual cases of foodborne illness, health departments keep track of outbreaks of foodborne illness. This occurs when a group of people eat the same contaminated food and two or more of them become sick. According to the CDC, about 400 to 500 outbreaks investigated by local and state health departments are reported each year.

Despite recent outbreaks, researchers report that the foods that Americans consume are now safer than in previous years.