Foodborne illness often shows itself as flu-like symptoms such as nausea, vomiting, stomach cramps, diarrhea or fever, so many people may not recognize it as a foodborne illness. The severity of the symptoms may depend on the quantity of food that was eaten and the age of the person. Young children and older adults are more susceptible to foodborne illness. People with compromised immune systems also may be more susceptible. The onset of symptoms ranges from a few hours to two or more days after the contaminated food was eaten.

Bacteria or other pathogens on food cause Foodborne illness. Thousands of types of bacteria are naturally present in our environment, but only some bacteria cause disease in humans. Bacteria that cause illness are called "pathogens." When certain pathogens enter the food supply, they can cause foodborne illness.

Estimates of people affected by foodborne illness range from 3.3 million to 12.8 million cases each year and 3900 deaths each year, according to the USDA's Economic Research Service. The reason for the large range is that many people attribute their illness to "24 Hour Flu" and do not report it or seek treatment for foodborne illness.