Studies of the Acute Diarrheal Diseases: XIII. Cultural Surveys of Normal Population Groups

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Abstract
Representative samples of the general population of New Mexico, Georgia, New York City, and Puerto Rico were cultured for Shigella. Records of the occurrence of diarrheal disease were obtained by the historical method and through visiting families at monthly intervals. The average revealed prevalence of S. para-dysenteriae in these areas was 11% in New Mexico, 4% in Puerto Rico, 3% in Georgia, and 0.1% in New York City. This prevalence was highest in children 1-9 yrs. of age, approx. twice that for infants or for older children and adults. The total reported or estimated annual morbidity from the diarrheal diseases was 60% in Puerto Rico, 48% in New Mexico, 20% in Georgia, and markedly less in New York City. The illnesses were common in young children but decreased progressively from age 2 to 5 yrs. The seasonal variation in the incidence of disease was more consistent and more marked than seasonal differences in the prevalence of Shigella infections. Infection without disease was rare in infants, and the number of carriers per case progressively increased with age up to 5 yrs., but thereafter significant variations were not found. For all ages there was an average of 9.1 convalescent or passive carriers for each current case. The ratio of passive carriers to current and recent cases was lower, but varied similarly by age and was strikingly uniform for the different vars. of Shigella. "Manifest human sources" of Shigella infection were rare when compared with the number of "hidden sources" found in these surveys. Knowledge of the unrecognized infections (hidden sources) is essential for an understanding of the epidemiology of Shigella infections.

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