Background

On this page

• Transmission
• Symptoms
• Bacterial Foodborne Pathogens and their Toxins
• Viral Foodborne Pathogens
• Parasitic Foodborne Pathogens
• Prion Disease
• Algal Toxins in Seafood

Transmission

Foodborne illnesses are most commonly spread by consuming contaminated food or beverages or by touching body fluids or surfaces contaminated with feces containing foodborne pathogens and then touching the mouth (swallowing the pathogen by the oral route).

Symptoms

The most common symptoms of foodborne illness are:

• Diarrhea
• Stomach Cramps
• Nausea
• Vomiting
• Fever

The severity of symptoms experienced by an individual from foodborne illness depends on several factors. These include the type and species of pathogen ingested, how much of the organism was ingested, and the general health of the person who ingested the pathogen.

Symptoms can range from very mild to severe and can last hours to days. People with severe symptoms such as bloody diarrhea, diarrhea that lasts more than 3 days, fever of 102°F or higher, continuous vomiting, and signs of dehydration should seek medical help.

Bacterial Foodborne Pathogens and their Toxins

In the United States, consuming contaminated food, especially undercooked meat, or drinking water contaminated with bacteria are common causes of foodborne illness. Some of these bacteria release toxins, or poisons, that can worsen diarrhea or vomiting and may cause other serious complications (Table 1).

Salmonella species, for example, are present in about one in 25 packages of raw chicken sold at grocery stores. Likewise, illness from Campylobacter is most often caused by eating undercooked poultry and sometimes raw vegetables (such as those in salads) which have become contaminated during preparation on surfaces such as a cutting board that was used previously for raw meat. In addition, bacteria such as E. Coli can contaminate groundwater via agricultural runoff from animal farming activity. This contaminated water can then affect the soil where fruit and vegetables are grown. While washing produce may remove some contaminants, certain pathogens can adhere to rough or creviced surfaces such as the rind of a cantaloupe, or grow inside porous, leafy vegetables like romaine lettuce.

Viral Foodborne Pathogens

Foodborne viruses are easily spread from person to person. Like bacteria, they can spread via the fecal-oral route but can also spread via saliva (talking, sneezing or coughing, etc.). They can be spread from water or food contaminated with agricultural runoff or sewage but do not grow in food like bacteria. Instead, large numbers of viral particles are shed from infected people onto surfaces and in food and beverages where they can survive and remain infective for days or weeks before entering a host.

The most common cause of foodborne illness in the United States is Norovirus, also known as Norwalk virus. Norovirus is estimated to cause illness in over 5 million people and almost 23,000 hospitalizations every year.

Because norovirus is highly contagious, it sickens many people in congregate settings where people have close contact and use the same food and water sources. Illnesses from norovirus occur frequently on cruise ships, in hospitals and nursing homes, and in childcare facilities. Norovirus transmission on cruise ships has become a frequent cause of concern among travelers, cruise line industry leaders, and public health professionals.

Symptoms of most foodborne viruses are similar to those of foodborne bacteria and may include nausea, vomiting, stomach pain or cramps, and diarrhea, fever, malaise, and muscle aches. Treatment for foodborne viruses generally includes hydration and symptom management because these illnesses are self-limiting, meaning that they go away on their own.

Exceptions are Hepatitis A virus (HAV), Hepatitis E virus (HEV), and poliovirus (polio), described in Table 2. These viruses are considered self-limiting but can result in severe and debilitating disease. There are, however, vaccines to prevent both polio and Hepatitis A.

Parasitic Foodborne Pathogens

In the United States, foodborne illnesses caused by parasites are less common than those caused by bacteria and viruses, and although symptoms (nausea, vomiting, diarrhea, and others) may be similar, they often develop more slowly. Parasitic infections are also harder to detect in clinical settings and often go undiagnosed or are misdiagnosed. In addition, detection of parasites is not included in routine food safety screenings, but instead is targeted at high-risk, imported food products.

Two of the most common foodborne parasites are the single-celled species, Cryptosporidium and Toxoplasma gondii (Figure 1A and 1B). Both have complex life cycles that consist of several life stages. Some parasites, including Toxoplasma require an animal or insect as intermediate host in order to fully develop. Other important foodborne parasites are shown in Table 3.

Figure 1. Life cycles of two common foodborne parasitic diseases in the United States

1. Cryptosporidium. Humans are the primary hosts for Cryptosporidium hominus while cows and other ruminants (hooved herbivores) are primary hosts for C. parvum, but many other mammals and birds can be infected. Infection in humans begins with ingestion of water or food contaminated with feces containing Cryptosporidium eggs (oocysts). Once infected, humans and animals pass the parasitic eggs in their stool (1), perpetuating the cycle (2, 3). Cryptosporidiosis, the resulting disease, can be severe and include stomach cramps; frequent, watery diarrhea; dehydration; and weight loss.
2. Toxoplasma gondii. Cats (1) are the primary hosts for T. gondii. Animals (mice, sheep, pigs and other mammals) exposed to parasite-infected cat feces can swallow the eggs. The animals are then infected, and the eggs mature and rapidly divide in their body forming cysts in their muscle tissue. Cats become infected when they eat infected mice, perpetuating the cycle. Humans who eat undercooked pork, lamb or other meat containing Toxoplasma cysts can acquire the Toxoplasma infection (2), as can people who have direct contact with infected cat feces (e.g., while cleaning litter boxes) (3). Finally, women who are pregnant can pass Toxoplasma though the placenta to their unborn child resulting in congenital toxoplasmosis, a disease that can cause premature birth, birth defects such as loss of sight, and long-term brain damage.
   Figures 1A and 1B were modified from the Public Health Image Library (PHIL), CDC.

Prion Disease

Variant Creutzfeldt-Jakob Disease (vCJD) is a very rare form of prion illness that can be acquired from ingesting beef from cattle with Bovine Spongiform Encephalopathy (BSE), otherwise known as “mad cow disease”. Prions are misfolded proteins that can trigger misfolding of other proteins in the brain. Ingesting infected meat can cause development of vCJD, the variant (human) form of BSE, which primarily affects young adults.

Most known cases of vCJD have occurred in the United Kingdom, but cases have occurred in other parts of the world, including four cases in the United States. Three of the four U.S. patients with vCJD were known to have contracted it outside of the country, and it is considered likely that the fourth patient also contracted vCJD abroad. BSE is now very rarely found in cows, so well-cooked beef in any country is considered to be free of the disease.

Algal Toxins in Seafood

Fish and shellfish that inhabit both fresh and saltwater consume algae as a regular part of their diet. These algae may contain toxins, particularly during algal blooms. Eating fish or shellfish that are wild caught (not commercially produced) during periods of algal blooms poses a serious risk to health. The toxins in algae are not pathogenic or communicable but are poisonous when eaten and result in Harmful Algal Bloom (HAB)-associated illness that can cause serious damage to organs and even death.

For more information about HAB-associated illness, See CDC’s websites:

• Symptoms Caused by Saltwater Harmful Algal Blooms
• Symptoms Caused by Freshwater Harmful Algal Blooms