Causes & Symptoms

Bacterial Causes of Foodborne Illness


Botulinum toxin (produced by Clostridium botulinum bacteria)

Symptoms: Neurotoxic symptoms, including double vision, inability to swallow, speech difficulty, and progressive paralysis of the respiratory system

Onset: Generally 4-36 hours after eating.

Source of Foodborne Illness: These bacteria produce toxins only in an anaerobic (oxygen-less) environment of little acidity. The spores are heat resistant and can survive in foods that are incorrectly or minimally processed. Most of the small number of outbreaks reported annually in the U.S. are associated with inadequately processed, home-canned foods, but occasionally commercially-produced foods have been involved in outbreaks. Sausages, meat products, canned vegetables and seafood products have been vehicles for human botulism.

Get medical help immediately. Botulism can be fatal. 


Campylobacter jejuni

Symptoms: Diarrhea, abdominal cramping, fever, and sometimes bloody stools. Lasts 7-10 days.

Onset: Generally 2-5 days after eating.

Source of Foodborne Illness: Bacteria on poultry, cattle, and sheep can contaminate meat and milk of these animals. Chief raw food sources: raw poultry, meat, and unpasteurized milk.

E-coli O157:H7

Escherichia coli O157:H7

Symptoms: Severe bloody diarrhea and abdominal cramps; sometimes the infection causes non-bloody diarrhea or no symptoms. Usually little or no fever is present, and the illness resolves in 5 to 10 days.

In some persons, particularly children under 5 years of age and the elderly, the infection can also cause a complication called hemolytic uremic syndrome (HUS), in which the red blood cells are destroyed and the kidneys fail. About 2%-7% of infections lead to this complication. In the United States, hemolytic uremic syndrome is the principal cause of acute kidney failure in children, and most cases of hemolytic uremic syndrome are caused by E. coli O157:H7.

Onset: Generally 2-5 days after eating.

Source of Foodborne Illness: The bacterium E. coli O157:H7 is a rare but dangerous type of E. coli. The organism can be found on a small number of cattle farms and can live in the intestines of healthy cattle. Meat can become contaminated during slaughter, and organisms can be thoroughly mixed into beef when it is ground. Bacteria present on the cow’s udders or on equipment may get into raw milk.

  • Eating meat, especially ground beef, that has not been cooked sufficiently to kill E. coli O157:H7 can cause infection. Contaminated meat looks and smells normal. Although the number of organisms required to cause disease is not known, it is suspected to be very small.
  • Among other known sources of infection are consumption of sprouts, lettuce, salami, unpasteurized milk and juice, and swimming in or drinking sewage-contaminated water.
  • Bacteria in diarrheal stools of infected persons can be passed from one person to another if hygiene or handwashing habits are inadequate.
  • This is particularly likely among toddlers who are not toilet trained. Family members and playmates of these children are at high risk of becoming infected.
  • Young children typically shed the organism in their feces for a week or two after their illness resolves. Older children rarely carry the organism without symptoms.


Listeria monocytogenes

Symptoms: Fever, headache, nausea, and vomiting. Primarily affects pregnant women and their fetuses, newborns, the elderly, people with cancer, and those with impaired immune systems. Can cause fetal and infant death.

Onset: From 7-30 days after eating, but most symptoms have been reported 48-72 hours after consumption of contaminated food.

Source of Foodborne Illness: Found in soft cheese, unpasteurized milk, hot dogs and deli meats, imported seafood products, frozen cooked crab meat, cooked shrimp, and cooked surimi (imitation shellfish). The Listeria bacteria resist heat, salt, and acidity better than many other micro-organisms. They survive and grow at refrigeration temperatures.

Perfringens food poisoning

Clostridium perfringens

Symptoms:  Abdominal pain and diarrhea, and sometimes nausea and vomiting. Symptoms last a day or less and are usually mild. Can be more serious in older or debilitated people.

Onset: Generally 8-12 hours after eating.

Source of Foodborne Illness:  In most instances, caused by failure to keep food hot. A few organisms are often present after cooking and multiply to toxic levels during cool down and storage of prepared foods. Meats and meat products are the foods most frequently implicated. These organisms grow better than other bacteria between 120-130° F. So gravies and stuffing must be kept above 140° F.


Salmonella bacteria

Symptoms: Diarrhea, fever, abdominal cramps, vomiting.

Onset: Generally 8-12 hours after eating.

Source of Foodborne Illness: Raw meats, poultry, eggs, milk and other dairy products, shrimp, frog legs, yeast, coconut, pasta and chocolate are most frequently involved.

Shigellosis (bacillary dysentery)

Shigella bacteria

Symptoms: Abdominal cramps, diarrhea, fever, sometimes vomiting, and blood, pus, or mucus in stool.

Onset: 1-7 days after eating.

Source of Foodborne Illness: Found in milk and dairy products, poultry, and potato salad. Food becomes contaminated when a human carrier does not wash hands and then handles liquid or food that is not thoroughly cooked afterwards. Organisms multiply in food left at room temperature.

Staphylococcal food poisoning

Staphylococcal enterotoxin (produced byStaphylococcus aureus bacteria)

Symptoms: Diarrhea, vomiting, nausea, abdominal pain, cramps, and prostration. Lasts 24-48 hours. Rarely fatal.

Onset: Generally 30 minutes-8 hours after eating.

Source of Foodborne Illness: Toxin produced when food contaminated with the bacteria is left too long at room temperature. Meats, poultry, egg products, tuna, potato and macaroni salads, and cream-filled pastries are good environments for these bacteria to produce toxins.

Vibrio Infection

Vibrio vulnificus

Symptoms: Chills, fever, and/or prostration. At high risk are people with liver conditions, low gastric (stomach) acid, and weakened immune systems.

Onset: Abrupt.

Source of Foodborne Illness: The bacteria live in coastal waters and can infect humans either through open wounds or through consumption of contaminated seafood. The bacteria are most numerous in warm weather.

Protozoa Causes of Foodborne Illness


Entamoeba histolytica

Symptoms: Severe cramping pain, tenderness over the colon or liver, loose morning stools, recurrent diarrhea, loss of weight, fatigue, and sometimes anemia.

Onset: 3-10 days after exposure.

Source of Foodborne Illness: Exist in the intestinal tract of humans and are expelled in feces. Polluted water and vegetables grown in polluted soil spread the infection.


Giardia lamblia

Symptoms: Sudden onset of explosive watery stools, abdominal cramps, anorexia, nausea, and vomiting. Especially infects hikers, children, travelers, and institutionalized patients.

Onset: 1-3 days.

Source of Foodborne Illness: Most frequently associated with consumption of contaminated water. May be transmitted by uncooked foods that become contaminated while growing or after cooking by infected food handlers. Cool, moist conditions favor organism’s survival.

Viral Causes of Foodborne Illness

Calcivirus  (Norwalk-like virus, Norovirus)

Symptoms: Nausea, vomiting, diarrhea, abdominal pain. Headache and low-grade fever may also accompany this infection. Lasts for 24 to 60 hours.

Onset: Generally 24-28 hours after exposure.

Source of Foodborne Illness: An extremely common cause of foodborne illness, and the leading cause of acute gastroenteritis, though rarely diagnosed, because the laboratory test is not widely available. Norwalk-like virus spreads primarily from one infected person to another. Infected persons can contaminate a salad, sandwich or other food as they prepare it if they have the virus on their hands.

Hepatitis A virus

Symptoms : Begins with malaise, appetite loss, nausea, vomiting, and fever. After 3-10 days patient develops jaundice with darkened urine. Severe cases can cause liver damage and death.

Onset: 1-10 days.

Source of Foodborne Illness: Mollusks (oysters, clams, mussels, scallops, and cockles) become carriers when their beds are polluted by untreated sewage. Raw shellfish are especially potent carriers, although cooking does not always kill the virus.