Rotaviruses Damage to microvilli Caliciviruses (noroviruses) Mucosal lesion Astroviruses Mucosal lesion Enteric adenoviruses Mucosal lesion
Campylobacter jejuni Invasion, enterotoxin Clostridium difficile Cytotoxin, enterotoxin
Enteropathogenic (EPEC) Adherence, effacement
Enterotoxigenic (ETEC) Enterotoxins (heat-stable or heat(traveler’s diarrhea) labile) Enteroinvasive (EIEC) Invasion of mucosa Enterohemorrhagic (EHEC) Adherence, effacement, cytotoxin (includes O157: H7 causing HUS) Enteroaggregative (EAEC) Adherence, mucosal damage Salmonella Invasion, enterotoxin Shigella Invasion, enterotoxin, cytotoxin Vibrio cholerae Enterotoxin Vibrio parahaemolyticus Invasion, cytotoxin Yersinia enterocolitica Invasion, enterotoxin
Entamoeba histolytica Invasion, enzyme and cytotoxin production; cyst resistant to physical destruction
Giardia lamblia Adheres to mucosa; cyst resistant to physical destruction
Spore-forming intestinal Adherence, inflammation protozoa (Enterocytozoon bieneusi, Encephalitozoon intestinalis)
HUS, Hemolytic uremic syndrome.
Typhoid fever is caused by Salmonella typhi and, occasionally, Salmonella paratyphi. Worldwide, there are an estimated 16 million cases of typhoid fever annually, resulting in 600,000 deaths. The typhoid bacillus infects humans only. These infections are distinguished by prolonged fever and extraintestinal manifestations, despite inconsistent presence of diarrhea. In the United States, approximately 400 cases of typhoid fever occur each year. Most occur in travelers returning from other countries. The incubation period of typhoid fever is usually 7 to 14 days (range 3 to 60 days). Infected persons without symptoms, or chronic carriers, serve as reservoirs and sources of continuous spread. Carriers often have cholelithiasis.
Nontyphoidal Salmonella produces diarrhea by invading the intestinal mucosa. The organisms are transmitted through
Table 112-2 Mechanisms of Infectious Diarrhea PRIMARY MECHANISM DEFECT STOOL EXAMINATION EXAMPLES COMMENTS Secretory Decreased absorption, increased secretion: electrolyte transport Watery, normal osmolality; osmoles = 2 × (Na+ + K+) Cholera, toxigenic Escherichia coli (EPEC, ETEC); carcinoid, Clostridium difficile, Persists during fasting; bile salt malabsorption also may increase intestinal water secretion;
From Wyllie R: Major symptoms and signs of digestive tract disorders. In Kliegman RM, Behrman RE, Jenson HB, editors: Nelson Textbook of Pediatrics, ed 18,
Philadelphia, 2007, Saunders, Table 303-7, p 152. WBCs, White blood cells; infection may also contribute to increased motility.
contact with infected animals (chickens, pet iguanas, other reptiles, turtles) or from contaminated food products, such as dairy products, eggs, and poultry. A large inoculum, of 1000 to 10 billion organisms, is required because Salmonella is killed by gastric acidity. The incubation period for gastroenteritis ranges from 6 to 72 hours but usually is less than 24 hours.