The incidence and etiology of diarrheal disease in a group of 55 Egyptian village adults were studied by weekly clinical, bacteriological and parasitological observations over a period of eight months. There were, on the average, 1.2 episodes of diarrhea per subject during this time, or an estimated annual attack rate of 1,800 cases per 1,000. Shigella or Salmonella were demonstrated in 9 per cent of the episodes. The subjects were heavily parasitized with E. histolytica, A. lumbricoides and S. mansoni but it was difficult to associate the presence of these parasites with the diarrheal episodes.
Adults were infected with Shigella at about the same frequency as children living in the same environment, but a far greater percentage of the infections in adults were asymptomatic with respect to diarrhea. This suggests that, under constant exposure, susceptibility to infection with Shigella decreases with age.
Present address: Naval Medical Research Institute, National Naval Medical Center, Bethesda 14, Maryland.