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Acute diarrheal disease is a leading cause of illness globally and is associated with an estimated 1.4 million deaths per year. Among children <5 years of age, diarrheal disease is second only to lower respiratory infection as the most common infectious cause of death. The incidence rate of diarrheal disease among children in low- and middle-income countries is estimated to be 2.9 episodes per child per year, for a total of 1.7 billion episodes annually. The morbidity from diarrhea is also significant. Recurrent intestinal infections are associated with physical and mental stunting, wasting, micronutrient deficiencies, and malnutrition. In short, diarrheal disease is a driving factor in global morbidity and mortality.
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The wide range of clinical manifestations of acute gastrointestinal illnesses is matched by the wide variety of infectious agents involved, including viruses, bacteria, and parasites (Table 30-1). This chapter discusses factors that enable gastrointestinal pathogens to cause disease, reviews host defense mechanisms, and delineates an approach to the evaluation and treatment of patients presenting with acute diarrhea. Individual organisms causing acute gastrointestinal illnesses are discussed in detail in subsequent chapters.
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PATHOGENIC MECHANISMS
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Enteric pathogens have developed a variety of tactics to overcome host defenses. Understanding the virulence factors employed by these organisms is important in the diagnosis and treatment of clinical disease.
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The number of microorganisms that must be ingested to cause disease varies considerably from species to species. For Shigella, enterohemorrhagic Escherichia coli, Giardia lamblia, or Entamoeba, as few as 10–100 bacteria or cysts can produce infection, while 105−108 Vibrio cholerae organisms must be ingested to cause disease. The infective dose of Salmonella varies widely, depending on the species, host, and food vehicle. The ability of organisms to overcome host defenses has important implications for transmission; Shigella...