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Food Poisoning (cont.)

What are the causes of food poisoning?

Viruses and bacteria

Viruses are the most frequent cause of food poisoning in the U.S. The next highest causes are bacteria. About 31 viral and bacterial pathogens are responsible for almost 9.4 million diagnosed food poisoning illnesses per year; about 39 million food poisoning cases are unspecified (undiagnosed). Yearly, about 128,000 people are hospitalized and about 3,000 die from all causes of food poisoning.

The most common pathogens that cause food poisoning are:

  1. Norovirus
  2. Salmonella
  3. Clostridium perfringens
  4. Campylobacter
  5. Staphylococcus aureus

The most common pathogens that caused hospitalizations due to contamination of foods or fluids are:

  1. Salmonella
  2. Norovirus
  3. Campylobacter
  4. Toxoplasma gondii
  5. Escherichia coli (E. coli)

The most common pathogens that cause deaths are:

  1. Salmonella
  2. Toxoplasma gondii
  3. Listeria monocytogenes
  4. Norovirus
  5. Campylobacter

Infectious agents comprise the largest category of food poisoning, but as seen from the above top categories, viral infections comprise the bulk of infected patients but are far less likely to cause hospitalizations and deaths than Salmonella bacteria. Because the bulk of "unspecified" causes is probably similar to the makeup of the diagnosed causes, this grouping of viruses and bacteria is considered to be the main causes of food poisoning in the U.S.


There are many toxins that can cause food poisoning. Some are produced by bacteria on or in food and others are produced by plants and animals/fish or other organisms that are ingested. There are many plants and animals/fish that can be poisonous under certain conditions but they are encountered infrequently or under special conditions.

Various toxins and their sources
enterotoxinsMushroom toxinsScombroid toxin
exotoxinsBelladonaCiguatera toxin

Even though there are many bacterial, plant, and other toxins that can be ingested with food and water, they are usually limited to relatively small outbreaks.


Most parasites are ingested with contaminated food or water. Some of the parasites ingested include:


Certain chemicals are considered toxins that can cause food poisoning. Although there are over 80,000 chemicals used in the U.S., only a few have been well studied. While most do not enter into foods, some do and cause food poisoning. An example of such a chemical is mercury, found in drinking water and in fish such as tuna and marlin. Other examples of chemicals that can be toxic if enough contaminates food and water are pesticides, polychlorinated biphenyls, and lead.

The causes of food and water poisoning are numerous. This brief listing of causes should suffice as a framework to begin more detailed studies of food poisoning.

Medically Reviewed by a Doctor on 11/13/2015

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