FAQ: Humans as Hosts of Foodborne Disease

How do pathogens make people sick?

The pathogens or their toxins can damage or destroy host cells or processes, or they can induce a host response to their presence that is harmful to the human host. Foodborne illness is caused by: viral, bacterial, or parasitic infections; toxins produced during microbial growth in food; and toxins produced by algal and fungal species.

Foodborne diseases include infection, toxicoinfection, and intoxication. Foodborne infections occur when pathogenic microorganisms are ingested, colonize the intestine, and sometimes invade other tissues. Foodborne toxicoinfections arise when a microorganism from ingested food grows in the intestinal tract and releases toxin(s) that damage tissues or interfere with normal tissue/organ function. Foodborne microbial intoxications occur by ingestion of a food containing harmful toxins or chemicals produced by the microorganisms, frequently during their growth in the food.

How soon after eating a contaminated food will someone get sick?

Anywhere from less than an hour to more than a month, depending on the pathogen. Onset times of a few hours are not uncommon; neither are onset times of a couple of days or more. A longer onset time can make linking the illness to a specific food consumption situation more difficult because samples of contaminated food eaten several days ago are difficult to obtain. In addition, the number of foods consumed within a long potential exposure time frame is much greater than for those pathogens that cause illnesses within a few hours of consumption. Furthermore, the dose of pathogen can influence the rate and intensity of onset.

How long does foodborne illness last? Again, the length of illness varies greatly. Some illnesses resolve within a day or two, but others linger for several days or even weeks. In addition to acute illness, some foodborne pathogens cause chronic disease, which may last for the rest of the victim’s life.

When several people eat the same contaminated food, why do only some people become ill?

First, the contamination may not be evenly distributed throughout the food, so everyone eating the food may not be exposed. Of those exposed to the pathogen, some may consume a greater number of pathogenic cells than other people, increasing the risk of illness.

Once the pathogen is ingested, the function of the individual’s immune system plays a crucial role. Any factor that reduces immune system function will increase the risk of foodborne disease. Children’s immune systems have not fully developed, putting them at greater risk. Similarly, the elderly are at greater risk because as people age the function of the immune system begins to decline. Others with poorly functioning immune systems include people with AIDS, transplant recipients, people with underlying medical conditions such as diabetes, and people on certain types of medication.

Are there some foods that people should avoid because they are more likely to contain foodborne pathogens?

Most healthy people can safely eat a rich and varied diet with minimal risk, as long as the food had been properly handled and prepared. The key is proper food safety practices. For example, to be safe, certain foods must be fully cooked. Fresh produce should be rinsed and carefully handled to prevent cross contamination by foods that require cooking. Once cooked, hot foods must remain hot for as long as they are available for consumption, or they must be refrigerated promptly to prevent pathogen growth.

Unfortunately, some people must avoid certain high-risk foods. For example, pregnant women are cautioned to avoid foods such as soft cheeses because of the risk of Listeria monocytogenes. Because certain foods are more likely to contain specific pathogens, individuals particularly susceptible to those pathogens must exercise special caution.

What can people do to reduce their susceptibility to illness?

Maintaining good overall health is the best way to minimize susceptibility to foodborne illness. A healthy life-style, including a balanced diet and avoiding stress, helps the immune system function properly. Consumption of probiotics—which are “good” bacteria that can promote gastrointestinal health—also may reduce susceptibility. Vaccines are available for only a very few foodborne pathogens, but more vaccines may become available in the future.

In addition to general immune system function, stomach acidity appears to play a role in susceptibility to foodborne illness. Antacids and medications that suppress acid production in the stomach may increase susceptibility to acid-sensitive pathogens because more pathogenic cells are likely to survive passage through the stomach into the small intestine. For this reason, the widespread use of increasingly powerful antacids and acid-reducing medications is cause for concern. Antacids that neutralize excess stomach acid may be preferable, from a food safety standpoint, to those longer acting medications that suppress acid production. Similarly, drinking large quantities of liquids such as water can dilute stomach acids and promote pathogen survival. Taking antibiotics can disrupt the naturally occurring microorganisms in the gastrointestinal tract, making it easier for pathogens to colonize, and medications that slow the passage of food through the gastrointestinal tract also can aid pathogen colonization. These examples demonstrate the complex relationship between food consumption, diet practices, and susceptibility to foodborne pathogens.

What can people do to reduce their exposure to foodborne pathogens?

Good food handling and preparation practices can have a tremendous impact on exposure to foodborne pathogens. Food handling behaviors—such as inadequate hand washing, unsafe storage temperatures that permit the growth of low levels of pathogens, incomplete cooking of potentially contaminated foods, and cross-contamination of fresh and cooked foods—can introduce pathogens into the food or fail to control pathogens already present.

Potential exposure to pathogens is not only a function of how food is handled, but also what foods individuals choose to eat. Similar to the link between poor sanitation practices and foodborne illness, consumption of certain foods can increase the risk of disease. The health benefit of certain foods, such as fresh produce, must be balanced against the risk of pathogens, especially for those people with increased susceptibility.

To help people reduce their risk of illness, the federal food safety agencies have created a web site (www.foodsafety.gov) that contains a wealth of excellent consumer advice on subjects ranging from food handling to diet selection for people with compromised immune system function.


Recognizing that food safety is a fundamental and continuing issue, the Institute of Food Technologists commissioned an expert panel to review the available scientific literature related to emerging microbiological food safety issues. The panel’s report is divided into seven sections: Introduction, Pathogenicity, Human Hosts, Microbial Ecology, Application of Science to Food Safety Management, Next Steps, and Conclusions. Copies of the report are available at www.ift.org. Founded in 1939, IFT is a 28,000 member nonprofit scientific society for food science and technology.