Significance of the incidence of Shigella infection as indicated by results of a longitudinal study.

A total of 1602 routine rectal swab specimens and 341 diarrhoeal specimens were obtained over a period of one and a quarter years from a group of children of semi-urban areas in the town of Vellore, North Arcot District, Tamil Nadu, India. Shigellae were found in 16.1 % of the specimens obtained at the time of diarrhoeal episodes. A 4.9 % incidence of asymptomatic infection with Shigella species was detected, with indication of a true passive carrier state in 3.0 %. The carrier-case ratio showed a significant difference and established the aetiologic significance of the Shigella group in juvenile diarrhoea. Shigella carriers were not found among babies 0-6 months old, but were found with increasing frequency with increase in age, in children of both sexes.