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.
Environmental factors play an important role in disease endemicity. Both water quality and water quantity are important. Although the degree of microbial contamination of water may be responsible for exposure to diarrhea-producing organisms, the availability of adequate amounts of water for personal and environmental cleansing, even if it is contaminated, may be beneficial. Sewage removal is a prerequisite for clean water and a healthful environment.Personal and food hygiene standards in a population are important to enteric infectious disease occurrence. Effective handwashing as a routine practice is practically unheard of in many areas of the developing world. Food all too often is improperly handled. Vegetables and fruits rarely are washed properly when reaching the house prior to preparation, despite the fact that they may have been exposed to human excreta used as fertilizer. Foods may be contaminated by unclean kitchen surfaces or hands. One of the most important errors in food hygiene is the storage of foods containing moisture at ambient temperatures between meals, which encourages microbial replication. This problem is especially severe during the warmer months. Medical care is often inadequate so that intestinal carriage of microbial pathogens and continued dissemination of the agents continue. Finally, underlying medical conditions can contribute both to the occurrence of diarrhea and to the severity of the resultant disease; measles and malnutrition are two important examples.
In most countries where acute diarrhea is a serious medical problem, it tends to be most prevalent during the warmer months. The reason is probably that bacteria grow rapidly in warm, moist conditions. Flies also can play a role in the transmission of enteric infections.
In day-care centers, when a non-toilet-trained child develops diarrhea, a variety of fecal organisms may spread to the hands of teachers and children, and to the toys shared by the children. Because of the efficient interchange of organisms during outbreaks, several pathogenic organisms are often identified during the same time period.
By employing optimal enteric microbiological techniques, an etiologic agent can be detected in approximately 50 percent of cases of acute diarrhea. The specific agent responsible for acute diarrhea will generally depend upon the age of the host, the geographic location, and the season. Table VIII.35.1 summarizes the most important etiologic agents in diarrhea, and Table VIII.35.2 indicates the microorganisms most frequently associated with diarrhea in certain settings.