A total of 23,262 fecal samples were examined between 1953 and 1956 from individuals in six different localities in Puerto Rico. The areas have been recognized as foci of schistosomiasis due to S. mansoni for many years.
The average prevalence of infection in the six localities declined from about 22 per cent in 1953 to 11 per cent in 1955. No definite control measures had been instituted, except for limited molluscicidal activity in Guayama, and chemotherapy among infected individuals in a small focus in another area.
Age and sex have been found important in the incidence of schistosomiasis due to S. mansoni. The data indicate that the greater number of cases arise between 10 and 20 years of age, and among males. Except for such places as Guayama, where the infection is an occupational hazard, it appears that the majority of infections may be acquired during the first 2 decades of life.