Gastroenteritis (Stomach Flu) - Causes

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What causes gastroenteritis?

Gastroenteritis, as defined above, has many causes, but the most frequent causes are viral (about 46%) and bacterial (about 40%) according to the CDC. Other causes vary greatly, such as parasites, toxins, food allergies, and medications. Many of the causes of gastroenteritis actually go on to develop additional gastrointestinal symptoms that are considered specific diseases themselves. The incidence of deaths due to gastroenteritis has been recently shown to be increasing. The two major causes of deaths are attributed to C. difficile, and Norovirus. In 2014, a new strain of Norovirus, termed Gll.4, first noted in Australia has caused more severe gastroenteritis, and has caused some outbreaks in the US. The following lists the major causes of gastroenteritis, and also lists the diseases that have symptoms of gastroenteritis as part of their specific disease process; this list is not all-inclusive but does include the large majority of causes of gastroenteritis that are encountered worldwide.


  • Norovirus: causes about 50% to 70% of all gastroenteritis in adults, the most common cause of gastroenteritis in the US, and second most common cause of death due to gastroenteritis.
  • Rotavirus: common cause of diarrhea in infants, occasionally producing dehydration
  • Adenovirus: usually causes respiratory infection, but some strains cause gastroenteritis symptoms
  • Astrovirus: common cause of diarrhea in infants
  • Sapovirus: common cause of mild gastroenteritis in children


  • Clostridium difficile: bacterial overgrowth and toxin production due to antibiotic suppression of competing intestinal bacteria; disease - C. difficile toxin production; this organism causes the highest number of deaths due to gastroenteritis, mainly in the elderly, over the age of 65 years.
  • Staphylococcus: - a frequent cause of diarrhea and abdominal cramps; disease - Staphylococcus food poisoning
  • Escherichia coli: food poisoning; diseases - E. coli infections, especially strain 0157:H7 that may cause HUS (hemolytic-uremic syndrome) or TTP (thrombotic thrombocytopenic purpura)
  • Salmonella: food poisoning; disease - salmonellosis
  • Shigella: food poisoning; disease - shigellosis
  • Listeria: usual source is contaminated dairy products; disease - listeriosis
  • Campylobacter: contaminated dairy foods
  • Vibrio: contaminated drinking water and seafood; disease - cholera
  • Bacillus: usual source is contaminated rice
  • Aeromonas: seafood contamination
  • Yersenia: pork meat contamination
  • Plesiomonas: oysters and other seafood


  • Giardia: common source of diarrhea from contaminated water; disease - giardiasis
  • Cryptosporidium: food and water sources of diarrhea; disease - cryptosporidiosis
  • Entamoeba: contaminated water; disease - amebiasis

Other causes of gastroenteritis

  • Food allergies: many types; eggs, nuts, milk, and shellfish are fairly common
  • Antibiotics: many antibiotics allow bacterial/fungal overgrowth (see Clostridium difficile previously mentioned)
  • Toxins: algal toxin in shellfish, heavy metal toxins. (aluminum, cadmium, arsenic, lead, and mercury) and others
  • Medications: side effects of many medications are diarrhea
Return to Gastroenteritis (Stomach Flu)

See what others are saying

Comment from: anonymous, 19-24 Male (Patient) Published: August 22

I am a young university student. It is the summertime, and having time off work, I've been lounging around, admittedly rarely showering. I went to McDonalds, ate (with dirty hands), came home, and suddenly started feeling waves of what seemed like knives stabbing me. I actually was squirming on the floor for the rest of the day. Really bad diarrhea has been present for a few days now along with a cough and fever. I actually started freaking out I may have HIV (will check to make sure though). Nasty bug! Wash your hands, friends.

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