Predicting the community prevalence of schistosomiasis mansoni from the prevalence among 7-to 14-year-olds

The World Health Organization suggested that the prevalence of Schistosoma mansoni among 7- to 14-year-olds be used to guide treatment strategies in e ndemic areas. This study explores how well the prevalence in that age group predicted the overall prevalence in the community in data from stool exami nations (Kato-Katz method) from 180 000 people in 3 municipalities in Brazi l in 1984 and 1985. The median prevalence was higher in 1984, before commun ity treatment was introduced. There was a strong relationship between the p revalence among 7- to 14-year-olds and the overall prevalence in the commun ity. We present sensitivities and positive predictive values for the use of prevalence in the indicator group to select communities for mass treatment as recommended by WHO. For a range of assumptions sensitivity and positive predictive value were never both above 80 %. We suggest that the estimates of validity presented in this paper inform future evaluations of strategie s for S. mansoni control.