Overview of Gastroenteritis

The most common bacterial causes of gastroenteritis are

• Campylobacter

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• Clostridioides difficile (C. diff)

• Escherichia coli (E. coli), especially strain O157:H7

• Salmonella

• Shigella

• Staphylococci, causing staphylococcal food poisoning

Bacterial gastroenteritis is less common than viral gastroenteritis. Bacteria cause gastroenteritis by various means.

Certain species, such as Vibrio cholerae and enterotoxigenic strains of E. coli, attach to the lining of the intestines without invading and produce enterotoxins. These toxins cause the intestines to secrete water and electrolytes, resulting in watery diarrhea.

Other bacteria (such as Staphylococcus aureus [see also Staphylococcal Food Poisoning], Bacillus cereus, and Clostridium perfringens) produce an exotoxin that can be present in contaminated food. The toxin can cause gastroenteritis without causing a bacterial infection. These toxins generally cause severe nausea, vomiting, and diarrhea. Symptoms begin within 12 hours of ingesting contaminated food and lessen within 36 hours.

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Some bacteria (such as certain strains of E. coli, Campylobacter, Shigella, Salmonella, and Clostridioides difficile) invade the lining of the small or large intestine (colon). There, they damage cells, causing sores (ulcerations) that bleed, and allow a considerable leakage of fluid containing proteins, electrolytes, and water. The diarrhea contains microscopic white and red blood cells and sometimes visible blood.

Salmonella and Campylobacter are common bacterial causes of diarrhea in the United States. Both infections are most frequently acquired from eating undercooked poultry. Unpasteurized milk is also a possible source. Campylobacter is occasionally transmitted by dogs or cats with diarrhea. Salmonella can be transmitted by eating undercooked eggs and by having contact with reptiles (such as turtles or lizards), birds, or amphibians (such as frogs and salamanders).

Species of Shigella are also a common bacterial cause of diarrhea in the United States and are usually transmitted person to person (especially in day care centers), although foodborne outbreaks occur.

E. coli gastroenteritis can be caused by several different subtypes of the bacteria.

Clostridioides difficile (C. diff) is now probably the most common bacterial cause of diarrhea in the United States and is the most common cause of diarrhea that occurs after treatment with antibiotics (see Drug-Related Gastroenteritis). However, it sometimes occurs in people who have not been treated with antibiotics. Antibiotics kill the healthy bacteria that normally reside in the intestines, which allows Clostridioides difficile bacteria to grow in their place. Clostridioides difficile produces a toxin that causes watery diarrhea that ranges from mild to severe and bloody (see also Clostridioides difficile-induced diarrhea).

Several other bacteria cause gastroenteritis, but most are rare in the United States. Yersinia enterocolitica can cause gastroenteritis or a syndrome that mimics appendicitis. A person is infected after ingesting undercooked pork, unpasteurized milk, or contaminated water. Several Vibrio species (such as Vibrio parahaemolyticus) cause diarrhea after ingesting undercooked seafood. Vibrio cholerae, which causes cholera, is responsible for the watery diarrhea that sometimes causes severe dehydration in people in low-resource countries. Epidemics may occur after natural disasters or in refugee camps. Listeria can rarely cause foodborne gastroenteritis but more often causes a bloodstream infection or meningitis in pregnant women, newborns, or older adults. Aeromonas is acquired from swimming in or drinking contaminated fresh water or briny, salty water. Plesiomonas shigelloides can cause diarrhea in people who have eaten raw shellfish or traveled to tropical regions in low-resource countries.

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