Accurate data on the frequency of acute diarrheal illness and the distribution of pathogens are not available for several reasons, including the facts that only a small fraction of cases come to the attention of physicians and that available diagnostic tests establish an etiology in only about half of these. In a survey of three groups of patients in a community (upper-middle class and lower class outpatients and hospitalized Infants), a possible cause was found in fewer than 20 percent of outpatients, and rotavirus accounted for the majority. However, asymptomatic colonization with rbtavirus is very common in early infancy, and demonstration of the antigen correlates with a causative role in diarrhea in only about one half of cases. Data on cases of shigellosis over a 15-year period in Dallas compared with the Centers for Disease Control national data demonstrate that epidemiologic patterns in any given community can differ substantially from the national data. Day-care centers are important sources of Glardia and Shigella infections in the community. The epidemiologic roles of newly reported causes of diarrhea (Campylobacter laridis, Blastocystis hominis, Cryptosporidium species, and Aeromonas hydrophila) are being explored. Generalizations about etiology and epidemiology of pathogens in diarrheal disease are Invalid unless the population group is defined socloeconomically and geographically.
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