Foodborne Illness

Foodborne illnesses are a collection of diseases that are caused by bacteria or harmful chemicals in the food we eat and drink. Most of these illnesses are caused by contaminated food when certain bacteria, viruses or parasites invade them. Others occur when food is contaminated by harmful chemicals or toxins. There are over 250 different diseases that have been described. It’s not surprising that since most of these infections or chemicals enter the body through the stomach and intestines, the most common symptoms are nausea, vomiting, diarrhea and abdominal pain.

In the early part of the 20th century typhoid fever and cholera were the most common diseases caused by bacteria contaminating our food and water supply. Today improvements in food processing and water treatment have just about eliminated these problems in the industrialized world. Unfortunately, other bacteria and viruses have taken their place and become common causes of foodborne disease, including Campylobacter, Salmonella, E. coli O157:H7, Shigella, Clostridium botulinium, Hepatitis A and Calciviruses. A bacterium called Vibrio parahemolyticus and a parasite called Cyclospora have been found to be the cause of a few recent outbreaks of food borne illnesses.

Uncooked or poorly cooked meats, raw eggs, and unpasteurized milk are the most common types of foods to be contaminated. Foods such as ground beef, pooled raw eggs or unpasteurized milk, which are prepared by combining sources from many different animals, are especially problematic, as a whole batch can be contaminated by one infected animal. Raw vegetables are also a problem, as they can be contaminated by washing with impure water or by fertilization with manure from infected animals. Raw shellfish are filter feeders and can be easily contaminated by sewage because these animals feed by straining large quantities of seawater.

Even properly prepared food can be cross contaminated when juices from raw foods are dripped onto cooked food or when utensils or cutting boards used for raw food are also used for cooked food.


Around the world, Campylobacter has become the most common bacteria causing food borne diarrhea. This bacterium lives in the intestines of birds, and can often contaminate raw poultry such as chicken. Eating undercooked chicken, or eating food contaminated by juices from raw chicken are easy ways of acquiring this illness. Symptoms include diarrhea that is often bloody, abdominal cramps and fever. Most people recover from Campylobacter diarrhea with no special treatment. The illness can also be treated with antibiotics such as erythromycin, ciprofloxacin or azithromycin. Rarely, patients can develop arthritis after an infection with Campylobacter. Guillain-Barre’ syndrome is a rare complication of infection; it affects a small number of people who develop a type of paralysis typically 2-4 weeks after recovering from Campylobacter infection.

Escherichia coli O157:H7

Escherichia coli (E. coli) bacteria can be typically found in everyone’s colon, and most types of E coli cause no problems at all. Certain types of E. coli can however cause severe illness, most notably diarrhea. E. coli O157:H7 is a particular type of E. coli that lives in the intestines of mammals such as cattle. We can become ill when we eat food contaminated by feces of animals infected with this organism. Hamburger meat is often a common source, as the grinding process allows organisms that were only on the surface of meat to be mixed throughout. Outbreaks of E. coli O157:H7 have also been cause by eating contaminated salami, lettuce and alfalfa sprouts, or drinking unpasteurized milk and apple juice, and contaminated well water.

E. coli O157:H7 can cause severe and bloody diarrhea with painful abdominal cramps. Most people recover without problems in 5 to 10 days. Unfortunately antibiotics are not particularly helpful. Less than one in twenty patients, most commonly children, can develop a severe complication with low blood count, bleeding, and kidney failure, called hemolytic uremic syndrome (HUS).

Enterotoxigenic E. coli is another type of E. coli that can cause severe watery diarrhea. It is very common in developing countries, where it’s often spread on unwashed fruits and vegetables, as well as in drinking water. It is probably responsible for the majority of traveler’s diarrhea, and is very likely the leading cause of childhood diarrhea in developing countries.


Salmonella is a bacteria found in the intestines of birds, reptiles and mammals. It is often spread through consumption of raw poultry, eggs, meat, and unwashed fruit. A person with this illness usually develops fever, diarrhea and abdominal cramps. Most people will improve on their own, without the need for antibiotics, and typically just require oral hydration. Some more severely ill patients require antibiotics, intravenous fluids and hospitalization. In people with weakened immune systems, salmonella can get into the bloodstream and cause severe illness and even death. Occasionally, people recovering from salmonella infection can develop irritated eyes, painful joints and pain with urination, a condition called Reiter’s syndrome. Some people infected with salmonella can have no symptoms at all, but become chronic carriers who can spread disease to others. This is where the term “Typhoid Mary” came from, Mary Mallon was a cook in the early 1900’s, who was never sick with salmonella, but had salmonella bacteria in her stool. Over the course of many years, many people she cooked for became ill, probably from bacteria passed to food from her hands.


Shigellosis, also known as bacillary dysentery, is caused by Shigella bacteria. It is also spread through eating contaminated food and drink. Persons with this infection develop fever, bloody diarrhea, and abdominal pain. Although patients can usually recover without any specific treatment, many patients are treated with antibiotics once they are diagnosed.


Botulism is a disease caused by a toxic chemical produced by a bacterium called Clostridium botulinum. This bacteria grows best in sealed containers such as cans that have not been heated enough to kill the bacterial spores. This bacteria thrives in places where there is little or no oxygen. It produces a toxin that can cause paralysis, breathing failure, and even death. Patients ingesting this toxin can develop double vision, drooping eyelids, slurred speech, difficulty swallowing, and difficulty breathing.

The Centers for Disease Control has simple recommendations for how to decrease the risk of developing a foodborne disease.

  • Cook meat, poultry and eggs thoroughly
  • Separate cooked and uncooked food. Avoid cross-contamination by not using platters or utensils contaminated by raw foods for cooked foods. Put cooked foods on clean platters, not the ones that held the raw meat.
  • Chill leftovers promptly. Don’t leave food out for more than 4 hours
  • Clean produce. Wash hands before preparing food and immediately after handling raw foods.
  • Report suspected food borne illness to the local health department.