Merck Manual

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Microorganisms That Cause Gastroenteritis

Microorganisms That Cause Gastroenteritis


Common Sources


Antimicrobial Use


Fecal-oral transmission*

Milder watery diarrhea

Vomiting and fever

Symptoms begin 3 to 4 days after infection

Usually lasts 2 to 7 days

Similar to rotavirus

Antibiotics and antiviral drugs are not given.

Eating contaminated meat (especially undercooked poultry)

Drinking contaminated water or unpasteurized milk

Occasionally transmitted by dogs or cats with diarrhea

Watery and sometimes bloody diarrhea

Usually lasts about 1 week

Antibiotics given in the early stages of illness may shorten the duration of symptoms (for example, azithromycin or ciprofloxacin).

Usually due to bacterial overgrowth of Clostridioides difficile in people who have been taking antibiotics

Diarrhea ranging from slightly loose stools to bloody diarrhea

Typically begins 5 to 10 days after starting antibiotics but may occur on the first day or up to 2 months later

Antibiotic that caused the illness is stopped.

Vancomycin or fidaxomicin is given by mouth.

Metronidazole may be given by mouth to people who cannot tolerate vancomycin and fidaxomicin.

Drinking contaminated water or eating contaminated food

Person-to-person contact

Recreational water exposure

People with impaired immune systems are particularly susceptible

Watery diarrhea and sometimes crampy abdominal pain, nausea, fatigue, and vomiting

Usually lasts 1 to 2 weeks

Antiparasitic drugs are sometimes given (for example, nitazoxanide).

Eating or drinking contaminated food or water

Oral-anal sex with an infected partner

Sometimes bloody diarrhea, cramping abdominal pain, weight loss, and fever lasting 1 to 3 weeks

Can cause infection in liver and other organs

Antiparasitic drugs are given (for example, metronidazole or tinidazole then iodoquinol or paromomycin).

Eating contaminated foods that have not been prepared properly, such as undercooked ground beef, unpasteurized milk or juice, or untreated water

Swimming in contaminated pools, lakes, or water parks

Person-to-person contact

Touching infected animals and then putting fingers in the mouth

Sudden abdominal cramps, watery diarrhea that usually becomes bloody within 1 to 3 days

Eating or drinking contaminated food or water

Frequent watery diarrhea, nausea, vomiting, abdominal cramps

Symptoms begin 12 to 72 hours after ingesting contaminated food or water

Usually lasts 3 to 5 days

Antibiotics (for example, ciprofloxacin or levofloxacin) may help shorten duration of illness.

Azithromycin is given to children.

Drinking or eating contaminated water or food

Person-to-person contact, particularly in day care centers

Watery diarrhea, nausea, vomiting, and loss of appetite

Symptoms appear 1 to 14 days (average 7 days) after infection

More long-term illness (lasting several days to several weeks) may occur, with foul-smelling stools, abdominal bloating, gas, fatigue, and weight loss

Antiparasitic drugs are given (for example, tinidazole, metronidazole, or nitazoxanide).

Intestinal (enteric) adenovirus

Fecal-oral transmission*

Respiratory droplets

Frequent watery diarrhea lasts 1 to 2 weeks

Mild vomiting begins 1 to 2 days after diarrhea starts

Fever affects 50% of people

Symptoms begin 3 to 10 days after infection

Usually lasts 10 days or more

Antibiotics and antiviral drugs are not given.

Eating or drinking contaminated food or water

Can spread easily from person to person via fecal-oral transmission*

Frequent watery diarrhea, especially in adults

Vomiting, especially in children

Stomach cramps, fever, headache, and aches and pains

Symptoms begin 1 to 2 days after infection

Usually lasts 1 to 3 days

Antibiotics and antiviral drugs are not given.

Fecal-oral transmission*

Frequent watery diarrhea


Fever higher than 102° F (about 39°C)

Symptoms begin 1 to 3 days after infection

May last 5 to 7 days in infants and young children

Antibiotics and antiviral drugs are not given.

Vaccines are available for infants.

Eating contaminated food

Contact with reptiles (for instance, iguanas, snakes, and turtles), birds, or amphibians (for instance, frogs and salamanders)

High fever, exhaustion, abdominal cramps, nausea, vomiting, diarrhea that may or may not be bloody

Symptoms usually last 1 to 4 days

Antibiotics usually are not given.

Person-to-person contact, especially in day care centers

May be mild or severe

In mild cases, low fever, watery diarrhea

In severe cases, high fever, exhaustion, severe abdominal cramps, painful passage of stool containing blood and mucus

In adults, symptoms usually last about 4 to 8 days in mild cases and to 3 to 6 weeks in severe cases without treatment

In most children, symptoms resolve by the 2nd week

Antibiotics are not routinely required for healthy adults with mild infection.

Antibiotics (for example, azithromycin and ceftriaxone) are given to people who are very young or very old, who have a weakened immune system, or who have a moderate to severe infection.

Bacillus cereus

Eating food contaminated by toxins produced by bacteria

Severe nausea, vomiting, and diarrhea

Symptoms begin 30 minutes to 8 hours after eating contaminated food and lessen within 24 hours

Antibiotics are not given.

Eating or drinking contaminated food or water

Painless, watery diarrhea and vomiting

Can lead to massive fluid loss and shock

Antibiotics are given (for example, ciprofloxacin or doxycycline).

Vaccines are available for adults.

Other types of Vibrio


Watery diarrhea, often with little nausea or vomiting

Antibiotics are given (for example, ciprofloxacin or doxycycline).

* Fecal-oral transmission involves infection that occurs after people touch their mouth after touching an object (such as a diaper or toy) contaminated by infected stool.