Infectious gastroenteritis and travelers' diarrhea

Definition

Gastroenteritis is inflammation of the lining of the stomach and small and large intestines. Most cases are infectious, caused by viruses, bacteria or parasites; less often it follows ingestion of drugs or chemical toxins. Transmission is foodborne, waterborne, person to person or occasionally from animals. Most episodes are self-limited.

Travelers' diarrhea is gastroenteritis in travelers, usually caused by bacteria endemic to local water.

Classification

By mechanism:

• viral: viruses infect enterocytes of the small-bowel villi; fluid and electrolytes pass into the lumen, and unabsorbed carbohydrates worsen diarrhea osmotically; watery diarrhea, blood and leukocytes in stool are uncommon
• enterotoxin-mediated: e.g. Vibrio cholerae and enterotoxigenic E. coli adhere to the mucosa without invading; their toxins stimulate adenylate cyclase and cause watery diarrhea
• by preformed toxins in food: e.g. Staphylococcus aureus, Bacillus cereus, Clostridium perfringens; nausea, vomiting and diarrhea within 12 hours, resolving within 36 hours
• invasive: e.g. Shigella, Salmonella, Campylobacter, C. difficile, some E. coli subtypes; ulceration, bleeding and protein-rich exudate, leukocytes and erythrocytes in stool

For stool testing, acute watery, subacute or chronic watery and acute inflammatory diarrhea are distinguished.

Occurrence & epidemiology

Worldwide, an estimated 1.6 million people die each year of infectious gastroenteritis. In the United States, about one in six people contract a foodborne illness each year. Viruses are the most common cause in the United States, mainly norovirus and rotavirus:

• Norovirus: the most common cause of sporadic and epidemic viral gastroenteritis in all age groups; peak in the winter months (November to April); outbreaks especially on cruise ships and in nursing homes; incubation period 24–48 hours
• Rotavirus: mainly young children (peak 3–15 months); incubation period 1–3 days
• Astrovirus and adenovirus: mainly infants and young children

Bacterial gastroenteritis is less common than viral; common bacterial pathogens are Campylobacter, Salmonella, Shigella, E. coli and C. difficile. Travelers' diarrhea affects 30–70% of travelers within two weeks, depending on region and season.

Aetiopathogenesis

Typical sources of infection:

• Salmonella and Campylobacter: mostly undercooked poultry, also unpasteurized milk; Campylobacter occasionally from dogs or cats with diarrhea; Salmonella also from undercooked eggs and contact with reptiles, birds or amphibians
• Shigella: mostly person to person; Shigella dysenteriae type 1 produces Shiga toxin
• Yersinia enterocolitica: undercooked pork, unpasteurized milk, contaminated water
• Vibrio species: undercooked seafood; V. cholerae where clean drinking water is lacking
• Giardia: person to person (often in day care centers) or via cysts in water and food; Cryptosporidium: mostly via water, not easily killed by chlorine
• Norovirus: via water, food and person to person; highly contagious

Travelers' diarrhea: the most common cause is enterotoxigenic E. coli, followed by Campylobacter jejuni, Shigella, Salmonella and enteroaggregative E. coli. Infection occurs via water and food, also via ice cubes or food washed with local water. Drugs that lower gastric acid increase the risk of more severe illness.

Clinical features

Onset is usually sudden with loss of appetite, nausea, vomiting, abdominal cramps and diarrhea (with or without blood and mucus), often with malaise and myalgia. The abdomen may be distended and mildly tender; bowel sounds are hyperactive (unlike in paralytic ileus).

• Norovirus: acute vomiting, abdominal cramps and diarrhea over 1–3 days; in children vomiting predominates, in adults diarrhea; fever, headache and myalgia possible
• invasive bacteria (e.g. Shigella, Salmonella): more often fever, prostration and bloody diarrhea
• E. coli O157:H7: first severe abdominal cramps and watery diarrhea, bloody after 1–2 days; little fever; possible hemolytic uremic syndrome with kidney failure and hemolytic anemia
• Yersinia: right lower quadrant pain mimicking appendicitis
• Parasites: subacute or chronic, mostly non-bloody diarrhea, fatigue, loss of body weight; amebic dysentery is the exception
• Travelers' diarrhea: onset 12–72 hours after ingestion, rarely bloody, mostly mild

Consequences: fluid loss with hypotension and tachycardia up to hypovolemic shock with kidney failure; with predominant vomiting metabolic alkalosis with hypochloremia, with predominant diarrhea metabolic acidosis; hypokalemia. Very young, older and immunocompromised people are particularly at risk. After the illness, post-infectious irritable bowel syndrome and dyspepsia may occur.

Diagnosis

• History and examination: copious watery diarrhea, possibly contaminated food or surface water, recent travel, contact with ill people or animals; intake of antibacterial drugs in the past three months suggests C. difficile
• Acute watery diarrhea: probably viral; stool testing only if it persists
• Subacute or chronic watery diarrhea: testing for parasites (microscopy for ova and parasites, more sensitive antigen tests for Giardia, Cryptosporidium and Entamoeba histolytica)
• Acute inflammatory diarrhea: leukocytes in stool; stool culture for Salmonella, Shigella, Campylobacter and E. coli; with visible blood, specific testing for E. coli O157:H7 or Shiga toxin
• Multiplex PCR panels are increasingly used; a positive norovirus result is interpreted cautiously because of asymptomatic shedding
• Endoscopy in adults with bloody diarrhea and risk factors (e.g. inflammatory bowel disease, immunodeficiency)
• Travelers' diarrhea: usually no specific testing; fever, severe abdominal pain and bloody diarrhea suggest more serious disease

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Further reading (open access)

1. MSD Manual Professional: Overview of Gastroenteritis
2. MSD Manual Professional: Traveler's Diarrhea
3. MSD Manual Professional: Norovirus Gastroenteritis
4. StatPearls: Bacterial Gastroenteritis

Cross-references