Longitudinal study on Schistosoma japonicum infections in the Philippines. Incidence and prevalence among school children in Dagami Area, Leyte.

The annual incidence of Schistosoma japonicum infection was calculated from the record of the yearly examination among school children of Dagami Area, Leyte, Philippines. Data were processed mainly by the computer. Children were examined for eggs by the merthiolate formalin concentration technique and by the circumoval precipitin test (COPT) once a year in 3 consecutive school years (SY), SY 1974/75, 1975/76 and 1976/77. About 600 to 700 children were examined yearly and the ratios of cases rechecked after 1 year were about 30%. A method to calculate the overall incidence in children who were examined at different intervals, was newly established. The incidence appeared to rise rapidly in the survey period, being 25.59% and 41.30% by fecal examination and 10.74% and 21.27% by COPT in SY 1975/76 and 1976/77, respectively. From the combined results of fecal examination and COPT, the reliable values of incidence, however, were shown to be stable during 2 years such as 22.06% and 24.21%, respectively. The incidence estimated by the age prevalence data was 20.25% in SY 1976/77 by the combined results and was found to be lower than the directly calculated value.