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Food Poisoning

Food poisoning refers to an illness that is caused by the presence of bacteria, poisonous chemicals, or another kind of harmful compound in a food. Bacterial growth in the food is usually required. Food poisoning is different from food intoxication, which is the presence of preformed bacterial toxin in food.

There are over 250 different foodborne diseases. The majority of these are infections, and the majority of the infections are due to contaminating bacteria, viruses, and parasites. Bacteria cause the most food poisonings. The United States Centers for Disease Control and Prevention estimates that 76 million Americans become ill each year from food poisoning. The cost to the economy in medical expenses and lost productivity is estimated at $5–6 billion per year. Infections with the common food-borne bacteria called Salmonella alone exacts about a $1 billion economic toll per year.

Aside from the economic costs, food poisoning hospitalizes approximately 325,000 Americans each year, and kills more than 5,000 Americans.

Food intoxication is technically separate from food poisoning. But, because food intoxication and food poisoning both cause foodborne illness, two noteworthy bacteria responsible for food intoxications will be mentioned.

Contamination by Staphylococcus is the most common cause of food poisoning. The bacteria grow readily in foods such as custards, milk, cream-filled pastries, mayonnaise-laden salads, and prepared meat.

Two to eight hours after eating, the sudden appearance of nausea, stomach cramps, vomiting, sweating, and diarrhea signal the presence of food poisoning. Usually only minor efforts need be made to ease the symptoms, which will last only a short time even if untreated. Over-the-counter preparations to counter the nausea and diarrhea may help to cut short the course of the condition. Recovery is usually uneventful.

This syndrome is especially prevalent in summer months when families picnic out of doors and food can remain in the warmth for hours. Bacterial growth is rapid under these conditions in lunchmeat, milk, potato salad, and other picnic staples. The first course of eating may be without consequences, but after the food remains at ambient temperature for two hours or more, the probability of an infectious bacterial presence is increased dramatically. The second course or mid-afternoon snacks can lead to an uncomfortable sequel.

A far more serious form of food intoxication results from a toxin secreted by the bacterium Clostridium botulinum. This infection is called botulism and is frequently fatal. The bacterium differs in that it grows under anaerobic conditions in food that has been improperly preserved.

Botulism is a hazard of home canning of food and can develop from commercially canned products in which the can does not maintain the sterile environment within it. Affected food has no tainted taste. Normal heating of canned products in the course of food preparation will neutralize the toxin but will not kill the bacterial spores. These will open inside the body, the bacterium will multiply, and sufficient toxin can be produced to bring about illness.

Ingestion of botulism-contaminated food does not lead to the gastric symptoms usually associated with food poisoning. Botulism toxin affects the nervous system, so the symptoms of botulism may involve first the eyes, with difficulty in focusing, double vision, or other conditions, then subsequent difficulty in swallowing and weakness of the muscles in the extremities and trunk. Death may follow. Symptoms may develop in a matter of hours if the tainted food has been consumed without heating, or in four to eight days if the food is heated and the bacterium needs the time to grow.

Diagnosis is made through observation of the symptoms and by culturing the bacterium from the suspected food source. Up to 65% of individuals infected with botulism die, usually within two to nine days after eating the affected food. Treatment of botulism usually requires the patient to be hospitalized to receive specific antitoxin therapy.

The most common foodborne bacterial infections are caused by Campylobacter, Salmonella, and a type of Escherichia coli designated O157:H7. The latter is the cause of "hamburger disease." A virus known as Calcivirus or Norwalk-like virus also is a common cause of food poisoning.

Travelers, especially those to foreign countries, often suffer pangs of gastric upset because of low sanitation levels in some areas. This type of food poisoning, which may actually stem from drinking the water rather than eating the food, is often called "tourista," "Montezuma's revenge," or "Delhi belly." The organisms contaminating the water can be the same as those that contaminate food (i.e., Salmonella and Escherichia coli).

Campylobacter is the most common cause of bacterial diarrhea. The bacteria live in the intestines of birds, and can be spread to the carcass upon slaughter. Eating undercooked chicken or food contaminated with the juices from raw chicken is a typical cause of Campylobacter food poisoning.

Salmonella is also found in the intestines of birds, as well as reptiles and mammals. It spreads to food because of contamination by feces; for example, by the handling of food by someone who did not washing their hands thoroughly after using the washroom. For most people, the infection is inconvenient, with cramping and diarrhea. But, for people in poor health or with malfunctioning immune systems, the bacteria can infect the bloodstream and threaten life.

Escherichia coli O157:H7 lives in the intestines of cattle. When it contaminates food or water, it can cause an illness similar to that caused by Salmonella. However, in a small number of cases, a much more devastating illness occurs. A condition called hemolytic uremic syndrome produces bleeding, can lead to kidney failure and, in the worst cases, can cause death.

The final common cause of foodborne illness is the Norwalk-like virus. It is also spread from feces to food, often again by handling of the food by someone who has not washed their hands. This type of foodborne illness is more difficult to diagnose, because not every testing laboratory has the equipment needed to detect the virus.

Food poisoning often affects numbers of individuals who have dined on the same meal. This enables physicians to trace the contaminated food and, if needed, determine the species of bacterium that is at fault.

Food poisoning is easily prevented. Proper handling of food includes washing the hands before preparing food, making certain that implements such as spoons and knives are clean, and providing proper cooling for foods that are most likely to nurture bacterial growth. Home canning must include careful and thorough heating of canned foods.



Latta, S.L. Food Poisoning and Foodborne Diseases. Berkeley Heights, NJ: Enslow Publishers. 1999.


Centers for Disease Control and Prevention. 1600 Clifton Road, Atlanta, GA 30333. (404) 639–3311 [cited October 22, 2002]. <http://www.cdc.gov/ncidod/dbmd/diseaseinfo/foodborneinfections_g.htm.>.

National Institutes of Allergy and Infectious Diseases, National Institutes of Health, 31 Center Drive, MSC 2520, Bethesda, MD 20892-2520 [cited October 22, 2002]. <http://www.niaid.nih.gov/factsheets/foodbornedis.htm.>.

Brian Hoyle


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—Growing bacteria on certain substrates such as beef broth, agar plates, or other nutrient medium.


—A heat-stable toxin produced in the cell wall of some bacteria.

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