Acute diarrheal illness can be defined as the sudden onset of the passage of a greater number of stools than usual that show a decrease in form. It is generally accompanied by other clinical symptoms such as fecal urgency, tenesmus, abdominal cramps, pain, nausea, and vomiting. In most cases the symptom complex is a result of intestinal infection by a viral, bacterial, or parasitic enteropathogen; occasionally it is secondary to ingestion of a microbial exotoxin.

Distribution and Incidence

Acute diarrhea is often hyperendemic in certain populations: infants and young children in developing tropical countries of Latin America, Africa, and southern Asia; persons traveling from industrialized to developing regions; military populations stationed in or deployed to tropical areas; and toddlers who are not toilet trained and are attending daycare centers. Diarrhea rates in children less than 5 years of age in developing countries range from between three and seven episodes per child each year. The rate of diarrhea for non-toilet-trained infants in day-care centers in urban areas of the United States is comparable to the rate of illness seen in Third World countries. Travelers’ diarrhea occurs in 20 to 40 percent of persons visiting high-risk areas from regions showing low disease endemicity. The rate of diarrhea occurrence in infants and young children under 5 years of age in the United States is approximately 0.8 to 1.0 episode per child each year. In all populations, acute diarrhea occurs less commonly in older children and adults than in infants.

Etiology and Epidemiology

The ultimate source of most of the enteric pathogens is infected humans, although for selected pathogenic organisms (i.e., Salmonella, Giardia), animals may serve as a reservoir.