Population-based study of the incidence of Shigella diarrhea and causativeserotypes in Santiago, Chile

Background Shigella is an important cause of diarrheal disease in children in developing countries. The increasing prevalence of antibiotic-resistant strains has stimulated interest in the use of multivalent Shigella vaccines . Because Shigella vaccines under development are based on eliciting immuni ty to O antigens, monitoring the distribution of serotypes in defined targe t populations is critical. We initiated health center-based surveillance in a poor semirural community in Colina, Santiago (7489 children <60 months o f age) to determine the age-specific incidence of Shigella disease and the responsible serotypes. Findings. Surveillance was maintained at the 2 health centers during warm s easons (November 1 through April 30) for 4 successive years (1994 to 1998), Shigella was recovered from 54 of 243 cases of dysentery (22%) and from 21 5 of 3966 cases of nondysenteric diarrhea (5.4%) (P < 0.001), The peak mean annual incidence of shigellosis occurred among children 12 to 47 months of age (9.0 to 12.6 cases/10(3) children), although the incidence in infants (5.2/10(3)) and children 48 to 59 months of age (6.2/10(3)) was also substa ntial. During the 1995 through 1996 season, an age matched healthy control was cultured for every child <60 months of age with diarrhea, Shigella isol ation from cases (34 of 576, 5.9%) was >8-fold higher than controls (4 of 5 76, 0.7%) (P < 0.01), Four serotypes, Shigella sonnei (45%), Shigella flexn eri 2b (19%), S. flexneri 2a (14%) and S. flexneri 6 (11%), accounted for 8 9% of all cases. Interpretation. Shigella remains an important pediatric pathogen in Santiag o. The serotype distribution from Colina, which closely resembles data from a population based surveillance study in Santiago in the mid-1980s, demons trates a remarkable degree of serotype stability in Santiago during a 15-ye ar period.