Gastroenteritis is inflammation of the lining of the stomach and small and large intestines. Most cases are infectious, although gastroenteritis may occur after ingestion of drugs, medications, and chemical toxins (eg, metals, plant substances). Acquisition may be foodborne, waterborne, person-to-person spread, or occasionally through zoonotic spread. In the United States, an estimated 1 in 6 people contracts foodborne illness each year. Symptoms include anorexia, nausea, vomiting, diarrhea, and abdominal discomfort. Diagnosis is clinical or by stool culture, although polymerase chain reaction testing and immunoassays are increasingly used. Treatment is supportive and directed at symptoms, but some parasitic and some bacterial infections require specific anti-infective therapy.
Most episodes of gastroenteritis are self-limited but cause uncomfortable symptoms. Electrolyte and fluid loss is usually little more than an inconvenience to an otherwise healthy adult but can be grave for people who are very young (see Dehydration in Children), who are older, or who are immunocompromised or have serious concomitant illnesses.
In the United States, each year about 48 million people contract a foodborne illness and 3,000 die of one (1).
Worldwide, an estimated 1.6 million people die each year of infectious gastroenteritis (2); although high, this number represents a significant decrease from previous mortality. Improvements in water sanitation in many parts of the world and the appropriate use of oral rehydration therapy for infants with diarrhea are likely responsible for this decrease.
General references
1. Centers for Disease Control and Prevention: Foodborne Germs and Illnesses. Accessed April 21, 2023.
2. GBD 2016 Diarrhoeal Disease Collaborators: Estimates of the global, regional, and national morbidity, mortality, and aetiologies of diarrhoea in 195 countries: A systematic analysis for the Global Burden of Disease Study 2016. Lancet Infect Dis 18(11):1211–1228, 2018. doi: 10.1016/S1473-3099(18)30362-1
Etiology of Gastroenteritis
Infectious gastroenteritis may be caused by viruses, bacteria, or parasites. Many specific organisms are discussed further in the Infectious Diseases section.
Viral gastroenteritis
Viruses are the most common cause of gastroenteritis in the United States, and most viral gastroenteritis is caused by
Most other viral gastroenteritis infections are caused by astrovirus or enteric adenovirus.
Astrovirus can infect people of all ages but usually infects infants and young children. In temperate climates, infection is most common in winter months, and in tropical regions, infection is more common in summer months. Transmission is by the fecal-oral route. Incubation is 3 to 4 days.
Adenoviruses are the 4th most common cause of childhood viral gastroenteritis. Infections occur year-round, with a slight increase in summer. Children < 2 years of age are primarily affected. Transmission is by the fecal-oral route as well as by respiratory droplets. Incubation is 3 to 10 days.
Viruses infect enterocytes in the villous epithelium of the small bowel. The result is transudation of fluid and electrolytes into the intestinal lumen; sometimes, unabsorbed carbohydrates resulting from malabsorption in the affected bowel subsequently worsen symptoms by causing osmotic diarrhea. Diarrhea is watery. Inflammatory diarrhea (dysentery), with fecal white blood cells (WBCs) and red blood cells (RBCs) or gross blood, is uncommon.
In patients with immunocompromise, additional viruses (eg, cytomegalovirus, enterovirus) can cause gastroenteritis.
Bacterial gastroenteritis
The bacteria most commonly implicated are
Escherichia coli (especially serotype O157:H7)
Staphylococci, causing staphylococcal food poisoning
Bacterial gastroenteritis is less common than viral. Bacteria cause gastroenteritis by several mechanisms.
Enterotoxins are produced by certain species (eg, Vibrio cholerae, enterotoxigenic strains of E. coli) that adhere to intestinal mucosa without invading. These toxins impair intestinal absorption and cause secretion of electrolytes and water by stimulating adenylate cyclase, resulting in watery diarrhea. C. difficile produces a similar toxin.
Exotoxins that are ingested in contaminated food are produced by some bacteria (eg, Staphylococcus aureus, Bacillus cereus, Clostridium perfringens). The exotoxin can cause gastroenteritis without bacterial infection. These toxins generally cause acute nausea, vomiting, and diarrhea within 12 hours of ingestion of contaminated food. Symptoms abate within 36 hours.
Mucosal invasion occurs with other bacteria (eg, Shigella, Salmonella, Campylobacter, C. difficile, some E. coli subtypes) that invade the mucosa of the small bowel or colon and cause ulceration, bleeding, exudation of protein-rich fluid, and secretion of electrolytes and water. The invasive process and its results can occur whether or not the organism produces an enterotoxin. The resulting diarrhea has evidence of this invasion and inflammation with WBCs and RBCs present on microscopy and sometimes with gross blood.
Salmonella and Campylobacter are common bacterial causes of diarrheal illness in the United States. Both infections are most frequently acquired through undercooked poultry; unpasteurized milk is also a possible source. Campylobacter is occasionally transmitted from dogs or cats with diarrhea. Salmonella can be transmitted by consuming undercooked eggs and by contact with reptiles, birds, or amphibians.
Species of Shigella are also common bacterial causes of diarrhea in the United States and are usually transmitted person to person, although foodborne epidemics occur. Shigella dysenteriae type 1, which is rare in the United States (1) produces Shiga toxin, which can cause hemolytic-uremic syndrome.
E. coli gastroenteritis can be caused by several different subtypes of the bacteria. The epidemiology and clinical manifestations vary greatly depending on the subtype.
In the past, Clostridioides difficile infection occurred almost exclusively in hospitalized patients receiving antibiotics. With the emergence of the hypervirulent NAP1 strain in the United States in the late 2000s, many community-associated cases are now occurring. C. difficile is now probably the most common bacterial cause of diarrhea in the United States (2).
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Several other bacteria cause gastroenteritis, but most are uncommon in the United States. Yersinia enterocolitica can cause gastroenteritis or a syndrome that mimics appendicitis because patients may have pain in the right lower quadrant. It is transmitted by undercooked pork, unpasteurized milk, or contaminated water. Several Vibrio species (eg, V. parahaemolyticus) cause diarrhea after ingestion of undercooked seafood. V. cholerae sometimes causes severe dehydrating diarrhea in regions where people lack access to clean drinking water and sanitary disposal of human waste and is a particular concern after natural disasters or in refugee camps. Listeria can rarely cause foodborne gastroenteritis but more often causes bloodstream infection or meningitis in pregnant women, neonates (see Neonatal Listeriosis), or older adults. Aeromonas is acquired from swimming in or drinking contaminated fresh or brackish water. Plesiomonas shigelloides can cause diarrhea in patients who have eaten raw shellfish or traveled to tropical low-resource regions.
Bacterial gastroenteritis references
1. Centers for Disease Control and Prevention (CDC): Shigella—Shigellosis: Questions & Answers. Accessed May 12, 2023.
2. Johnson S, Lavergne V, Skinner AM, et al: Clinical practice guideline by the Infectious Diseases Society of America (IDSA) and Society for Healthcare Epidemiology of America (SHEA): 2021 focused update guidelines on management of Clostridioides difficile infection in adults. Clin Infect Dis ciab549, 2021. doi: 10.1093/cid/ciab549
Parasitic gastroenteritis
The parasites most commonly implicated in high-resource countries are
Certain intestinal parasites, notably Giardia intestinalis (G. lamblia), adhere to the intestinal mucosa, causing nausea, vomiting, diarrhea, and general malaise. Giardiasis occurs in every region of the United States and throughout the world. The infection can become chronic and may cause a malabsorption syndrome. It is usually acquired via person-to-person transmission (often in day care centers) or from ingestion of cysts in contaminated water or food.
Cryptosporidium parvum causes watery diarrhea and can sometimes be accompanied by abdominal cramps, nausea, and vomiting. In healthy people, the illness is self-limited, lasting about 2 weeks. In patients with immunocompromise, illness may be severe and prolonged, causing substantial electrolyte and fluid loss. Cryptosporidium is usually acquired through contaminated water. It is not easily killed by chlorine and is the most common cause of recreational waterborne illness in the United States, accounting for about three fourths of outbreaks.
Other parasites that can cause symptoms similar to those of cryptosporidiosis include Cyclospora cayetanensis and, in patients with immunocompromise, Cystoisospora (Isospora) belli and a collection of organisms referred to as microsporidia (eg, Enterocytozoon bieneusi, Encephalitozoon intestinalis). Entamoeba histolytica (see Amebiasis) is a common cause of subacute bloody diarrhea in low-resource regions with poor sanitation but is rare in the United States. Amebiasis can cause an ulcerating colitis that mimics ulcerative colitis and must be excluded when that diagnosis is considered.
Symptoms and Signs of Gastroenteritis
The character and severity of symptoms of gastroenteritis vary.
Generally, onset is sudden, with anorexia, nausea, vomiting, abdominal cramps, and diarrhea (with or without blood and mucus). Malaise and myalgias may occur. The abdomen may be distended and mildly tender; in severe cases, muscle guarding may be present. Gas-distended intestinal loops may be palpable. Hyperactive bowel sounds are present on auscultation even without diarrhea (an important differential feature from paralytic ileus, in which bowel sounds are absent or decreased). Persistent vomiting and diarrhea can result in intravascular fluid depletion with hypotension and tachycardia. Hypovolemic shock with vascular collapse and oliguric renal failure may occur in severe cases.
If vomiting is the main cause of fluid loss, metabolic alkalosis with hypochloremia can occur. If diarrhea is more prominent, metabolic acidosis is more likely. Both vomiting and diarrhea can cause hypokalemia. Hyponatremia may develop, particularly if hypotonic fluids are used in replacement therapy.
Viral gastroenteritis
In viral infections, watery diarrhea is the most common symptom; stools rarely contain mucus or blood. For manifestations specific to norovirus and rotavirus, see Norovirus Gastroenteritis and Rotavirus Gastroenteritis.
The hallmark of adenovirus gastroenteritis is diarrhea lasting 1 to 2 weeks. Affected infants and children may have mild vomiting that typically starts 1 to 2 days after the onset of diarrhea. Low-grade fever occurs in about 50% of patients. Respiratory symptoms may be present. Symptoms are generally mild but can last longer than with other viral causes of gastroenteritis.
Astrovirus causes a syndrome similar to mild rotavirus infection.
Cytomegalovirus can cause bloody diarrhea in patients with immunocompromise.
Bacterial gastroenteritis
Bacteria that cause invasive disease (eg, Shigella, Salmonella) are more likely to result in fever, prostration, and bloody diarrhea.
E. coli O157:H7 infection usually begins with severe abdominal cramps and watery diarrhea for 1 to 2 days, followed by bloody diarrhea. Fever is absent or low grade.
The spectrum of illness with C. difficile infection ranges from mild abdominal cramps and mucus-filled diarrhea to severe hemorrhagic colitis and shock.
Bacteria that produce an enterotoxin (eg, S. aureus, B. cereus, C. perfringens) usually cause watery diarrhea. S. aureus and some strains of B. cereus predominantly cause vomiting.
Parasitic gastroenteritis
Parasitic infections typically cause subacute or chronic diarrhea. Most cause nonbloody diarrhea; an exception is E. histolytica, which causes amebic dysentery (see Amebiasis). Fatigue and weight loss are common when diarrhea is persistent.
Diagnosis of Gastroenteritis
Clinical evaluation
Stool testing in select cases
Other gastrointestinal disorders that cause similar symptoms (eg, appendicitis, cholecystitis, ulcerative colitis) must be excluded (see also evaluation of diarrhea).
Findings suggestive of gastroenteritis include the following:
Copious, watery diarrhea
Ingestion of potentially contaminated food (particularly during a known outbreak), untreated surface water, or a known gastrointestinal irritant
Recent travel
Contact with infected people or certain animals
E. coli O157:H7–induced diarrhea is notorious for appearing to be a hemorrhagic rather than an infectious process, manifesting as gastrointestinal bleeding with little or no stool. Hemolytic-uremic syndrome may follow as evidenced by renal failure and hemolytic anemia.
Recent oral antibiotic use (within 3 months) must raise suspicion for C. difficile infection. However, about one fourth of patients with community-associated C. difficile infection do not have a history of recent antibiotic use.
Stool testing
Stool testing is guided by clinical findings and the organisms that are suspected based on patient history and epidemiologic factors (eg, immunosuppression, exposure to a known outbreak, recent travel, recent antibiotic use). (See also the American College of Gastroenterology's 2016 clinical guideline for the diagnosis, treatment, and prevention of acute diarrheal infections in adults.) Cases are typically stratified into
Acute watery diarrhea
Subacute or chronic watery diarrhea
Acute inflammatory diarrhea
Multiplex polymerase chain reaction platforms that can identify causative organisms in each of these categories are being used more often (1). However, this testing is expensive, and because the categories are often distinguishable clinically or the disease courses are self-limiting, it is usually more cost-effective to test for specific microorganisms depending on the type and duration of diarrhea. In addition, polymerase chain reaction testing does not allow for antibiotic susceptibility testing.
Acute watery diarrhea is probably viral, and testing is not indicated unless the diarrhea persists. Although rotavirus and enteric adenovirus infections can be diagnosed using commercially available rapid assays that detect viral antigen in the stool, these assays are rarely indicated.
Subacute and chronic watery diarrhea require testing for parasitic causes, typically with microscopic stool examination for ova and parasites. Fecal antigen tests are available for Giardia, Cryptosporidia, and Entamoeba histolytica and are more sensitive than microscopic stool examination.
Acute inflammatory diarrhea without gross blood can be recognized by the presence of leukocytes on stool examination. Patients should have stool culture for typical enteric pathogens (eg, Salmonella, Shigella, Campylobacter, E. coli).
Acute inflammatory diarrhea with gross blood should also prompt testing specifically for E. coli O157:H7, as should nonbloody diarrhea during a known outbreak. Specific cultures must be requested because this organism is not detected on standard stool culture media. Alternatively, a rapid enzyme assay for the detection of Shiga toxin in stool can be done; a positive test indicates infection with E. coli O157:H7 or one of the other serotypes of enterohemorrhagic E. coli. (NOTE: Shigella species in the United States do not produce Shiga toxin.) However, a rapid enzyme assay is not as sensitive as culture. Polymerase chain reaction testing is used to detect Shiga toxin in some centers.
Adults with grossly bloody diarrhea may require endoscopic evaluation (sigmoidoscopy or colonoscopy) for further evaluation. Candidates for endoscopy include at-risk patients such as those with a history of inflammatory bowel disease or immunocompromise (in the case of suspected cytomegalovirus colitis). Appearance of the colonic mucosa may help diagnose amebic dysentery, shigellosis, and E. coli O157:H7 infection, although ulcerative colitis may cause similar lesions. Biopsy and culture are helpful in making a diagnosis.
Patients with a history of recent antibiotic use or other risk factors for C. difficile infection (eg, inflammatory bowel disease, use of proton pump inhibitors) should have a stool assay for C. difficile toxin, but testing should also be done in patients with significant illness even when these risk factors are not present because about 25% of cases of C. difficile infection currently occur in people without identified risk factors. Historically, enzyme immunoassays for toxins A and B were used to diagnose C. difficile infection. However, nucleic acid amplification tests targeting one of the C. difficile toxin genes or their regulator have been shown to have higher sensitivity and are now the diagnostic tests of choice in most cases.
General tests
Complete blood count (CBC) is nonspecific, although eosinophilia may indicate parasitic infection.
Renal function tests and CBC should be done about a week after the start of symptoms in patients with E. coli O157:H7 to detect early-onset hemolytic-uremic syndrome.
Diagnosis reference
1. Torres-Miranda D, Akselrod H, Karsner R, et al: Use of BioFire FilmArray gastrointestinal PCR panel associated with reductions in antibiotic use, time to optimal antibiotics, and length of stay. BMC Gastroenterol 20(1):246, 2020. doi: 10.1186/s12876-020-01394-w
Treatment of Gastroenteritis
Oral or IV rehydration
Consideration of antidiarrheal agents if C. difficile or E. coli O157:H7 infection is not suspected
Antibiotics only in select cases
Supportive treatment is all that is needed for most patients. Bed rest with convenient access to a toilet or bedpan is desirable.
Oral glucose-electrolyte solutions, broth, or bouillon may prevent dehydration or treat mild dehydration. Even if vomiting, the patient should take frequent small sips of such fluids; vomiting may abate with volume replacement. For patients with E. coli O157:H7 infection, rehydration with isotonic IV fluids may attenuate the severity of any renal injury should hemolytic-uremic syndrome develop. Children may become dehydrated more quickly and should be given an appropriate rehydration solution (several are available commercially—see Oral Rehydration). Carbonated beverages and sports drinks lack the correct ratio of glucose to sodium and thus are not appropriate, particularly for children < 5 years. If the child is breastfed, breastfeeding should continue. If vomiting is protracted or if severe dehydration is prominent, IV replacement of volume and electrolytes is necessary (see Intravenous Fluid Resuscitation).
When the patient can tolerate fluids without vomiting and the appetite has begun to return, food may be gradually restarted. Although commonly recommended, there is no demonstrated benefit to restricting the diet to bland food (eg, cereal, gelatin, bananas, toast). Some patients have temporary lactose intolerance.
Antidiarrheal (antimotility) agents are not recommended in pediatric cases and therefore should be avoided in children < 18 years of age with acute diarrhea (see also the Infectious Diseases Society of America's 2017 clinical practice guidelines for the diagnosis and management of infectious diarrhea). Use of antidiarrheal agents is contraindicated in children < 2 years of age. These agents are generally safe for adult patients with watery diarrhea (as shown by heme-negative stool). However, antidiarrheals may cause deterioration of patients with C. difficile or E. coli O157:H7 infection and thus should not be given to any patient with recent antibiotic use, heme-positive or bloody stool, or diarrhea with fever, pending specific diagnosis.
If vomiting
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Children who are still vomiting after 24 hours require reevaluation.
Although probiotics appear to briefly shorten the duration of diarrhea, there is insufficient evidence that they affect major clinical outcomes (eg, decrease the need for IV hydration and/or hospitalization) to support their routine use in the treatment or prevention of infectious diarrhea (1).
Probiotics reference
1. Preidis GA, Weizman AV, Kashyap PC, Morgan RL: AGA technical review on the role of probiotics in the management of gastrointestinal disorders. Gastroenterology 159(2):708–738.e4, 2020. doi: 10.1053/j.gastro.2020.05.060
Antimicrobials
Empiric antibiotics are generally not recommended except for certain cases of traveler’s diarrhea or when suspicion of Shigella or Campylobacter infection is high (eg, contact with a known case). (See also this expert panel's 2017 guidelines for the prevention and treatment of travelers' diarrhea.) Otherwise, antibiotics should not be given until stool culture results are known, particularly in children, who have a higher rate of infection with E. coli O157:H7 (antibiotics increase the risk of hemolytic-uremic syndrome in patients infected with E. coli O157:H7).
In proven bacterial gastroenteritis, antibiotics are not always required. They do not help with Salmonella and may prolong the duration of shedding in the stool. Exceptions include patients with immunocompromise, neonates, and patients with Salmonella bacteremia. Antibiotics are also ineffective against toxic gastroenteritis (eg, S. aureus, B. cereus, C. perfringens). Indiscriminate use of antibiotics fosters the emergence of drug-resistant organisms, increases the risk of adverse effects, and increases the potential for C. difficile infection. However, certain infections do require antibiotics (see table Selected Oral Antibiotics for Infectious Gastroenteritis).
Initial management of C. difficile colitis involves stopping the causative antibiotic if possible. The medication of choice to treat C. difficilevancomycinvancomycin or metronidazoleC. difficile infection (1).
Many centers are using fecal microbial transplantation for patients with multiple recurrences of C. difficile colitis. This treatment generally has been shown to be safe and effective, but there are still issues with quality control, particularly regarding infection transmission (see treatment of recurrences of C. difficile-induced diarrhea) (2C. difficile infection (3).
Antimicrobials references
1. Johnson S, Lavergne V, Skinner AM, et al: Clinical Practice Guideline by the Infectious Diseases Society of America (IDSA) and Society for Healthcare Epidemiology of America (SHEA): 2021 Focused update guidelines on management of Clostridioides difficile infection in adults. Clin Infect Dis 73(5):e1029–e1044, 2021. doi: 10.1093/cid/ciab549
2. Perler BK, Chen B, Phelps E, et alClostridioides difficile infection. J Clin Gastroenterol 54(8):701–706, 2020. doi: 10.1097/MCG.0000000000001281
3. Feuerstadt P, Allegretti JR, Khanna S: Practical use of RBX2660 for the prevention of recurrent Clostridioides difficile infection. Am J Gastroenterol 2023. doi: 10.14309/ajg.0000000000002195
Prevention of Gastroenteritis
Two live-attenuated oral rotavirus vaccines are available that are safe and effective against the majority of strains responsible for disease. Rotavirus immunization is part of the recommended infant vaccination schedule.
Prevention of infection is complicated by the frequency of asymptomatic infection and the ease with which many agents, particularly viruses, are transmitted from person to person. In general, proper procedures for handling and preparing food must be followed. Travelers should avoid potentially contaminated food and drink.
To prevent recreational waterborne infections, people should not swim if they have diarrhea. Infants and toddlers should have frequent diaper checks and should be changed in a bathroom and not near the water. Swimmers should avoid swallowing water when they swim.
Infants and other people with immunocompromise are particularly predisposed to developing severe cases of salmonellosis and should not be exposed to reptiles, birds, or amphibians, which commonly carry Salmonella.
Breastfeeding affords some protection to neonates and infants.
Caregivers should wash their hands thoroughly with soap and water after changing diapers, and diaper-changing areas should be disinfected with a freshly prepared solution of 1:64 household bleach (¼ cup diluted in 1 gallon of water). Children with diarrhea should be excluded from child care facilities for the duration of symptoms. Children infected with enterohemorrhagic E. coli or Shigella should also have two negative stool tests before readmission to the facility.
More Information
The following English-language resources may be useful. Please note that THE MANUAL is not responsible for the content of these resources.
American College of Gastroenterology: Clinical guideline for the diagnosis, treatment, and prevention of acute diarrheal infections in adults (2016)
Infectious Diseases Society of America: Clinical practice guidelines for the diagnosis and management of infectious diarrhea (2017)
Expert panel: Guidelines for the prevention and treatment of travelers' diarrhea (2017)
