Quantitative aspects of the epidemiology of Schistosoma japonicum infection in a rural community of Luzon, Philippines. WHO workshop.

In a rural community on the island of Luzon, Philippines, the overall prevalence of Schistosoma japonicum infection, based on stool examination performed by both a new modified quantitative thick smear and the merthiolate-iodine-formaldehyde concentration (MIFC) technique, was 49.5% in a total study population of 755 persons. Peak prevalence was observed in the 15-19-year age group, then decreased gradually. Although the total egg output was highest in the 15-19-year age group, individuals with high egg counts were found among all age groups.The prevalence and intensity of infection were higher in men than in women except in the 45-54-year age group. A small proportion (4.1%) of the study population (age range 6-53 years) excreted 50% of the eggs counted in this study. Liver and spleen enlargement were significantly associated with S. japonicum infection in all age groups. The frequency of a past history of dysentery and marked liver enlargement (>/= 5 cm) increased in parallel with increasing egg counts. Clustering of individuals with high egg counts in households was observed, but there was no correlation between geographical proximity of residence to potential transmission sites and household infection rates. An effective control strategy would be based on treatment of all infected persons in this endemic area rather than only a selected age group.