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Gastrointestinal infections can be caused by a wide variety of infectious agents, including bacteria, viruses, and parasites. In this chapter, common viral and bacterial causes of diarrhea will be discussed, followed by a discussion of the most important parasitic infections.

Bacterial and Viral Gastroenteritis

Patient Story

A 3-year-old boy who attends a child care center presents to his pediatrician with a 2-day history of bloody diarrhea with mucus. On physical examination, he is well hydrated and has mild abdominal tenderness. The pediatrician orders a stool culture for enteric pathogens and recommends supportive care including appropriate hydration and close follow-up. Forty-eight hours later, the stool culture is reported as positive for Shigella sonnei (Figure 179-1). Because the boy continued to have bloody diarrhea, the pediatrician treated the boy with a 5-day course of azithromycin and he recovered completely. Two stool cultures obtained after the completion of therapy were negative and the boy was able to resume child care.

FIGURE 179-1

Shigella colonies on a blood agar plate. (Used with permission from CDC Public Health Image Library.)


Gastrointestinal infections frequently manifest as diarrhea (loose, watery stools), frequently with fever, vomiting, and abdominal pain. Although many of these infections are self-limited, these infections can be associated with intestinal and extra-intestinal manifestations and can lead to significant morbidity.


  • Worldwide, diarrheal illness is a leading cause of morbidity and mortality.

  • Diarrhea accounts for 2 to 4 million health care visits, 220,000 hospitalizations, and 300 to 400 deaths annually in the US.1

  • Diarrhea is the most common illness encountered by international travelers to developing countries.2

  • Acquisition of intestinal pathogens occurs through the fecal-oral route, from person-to-person contact or from contaminated food and water. Many pathogens can be spread by either person-to-person contact or from contaminated food and water.

  • Pathogens that are spread through person-to-person contact include Shigella spp Escherichia coli O157:H7, and most viral causes of diarrhea. These agents are commonly implicated in outbreaks in childcare centers.

  • Pathogens that are spread through contaminated food and water include Salmonella spp Campylobacter spp, enterotoxigenic E coli, and many viruses.

  • Enterotoxigenic E coli Salmonella Campylobacter, and Shigella are the most common causes of traveler’s diarrhea.

  • Pet reptiles are common sources of Salmonella infection. Transmission of this organism to household members, especially young infants, can occur in the absence of direct contact in household. Salmonella bacteremia and meningitis has occurred from transmission from pet lizards.

Etiology and Pathophysiology

  • Common bacterial causes of gastroenteritis include Campylobacter spp, Salmonella spp, diarrheal-producing strains of E coli Shigella spp, and Yersinia spp.

  • Virulent traits of these agents include enterotoxins and cytotoxins that promote aggregation and invasiveness that result in clinical ...

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