CONTROL OF SCHISTOSOMA-HAEMATOBIUM MORBIDITY ON PEMBA ISLAND - VALIDITY AND EFFICIENCY OF INDIRECT SCREENING-TESTS

Four indirect screening methods for the detection of Schistosoma haema tobium morbidity are compared (history of haematuria, visual haematuri a, and microhaematuria at the 1+ and 2+ positivity limit by reagent st rips) in terms of their diagnostic performance under conditions of pro gressive decrease in prevalence of infection, intensity and risk of mo rbidity as a result of repeated schistosomiasis control programmes on Pemba Island, United Republic of Tanzania. The results show that the s ensitivity of a history of haematuria was higher (71%) in children but lower in adults (40%), similar to the findings for visual haematuria in children (60%) and adults (40%) at baseline. However, visual haemat uria had a higher specificity, positive predictive value, and efficien cy than a history of haematuria in both children and adults. Microhaem aturia at the 1+ positivity limit (by reagent strips) had the highest sensitivity of all the methods investigated but the lowest specificity , positive predictive value, and efficiency. Quantitatively, the indir ect methods tended to increase in specificity, negative predictive val ue, and efficiency during the course of the intervention programme. In contrast, positive predictive value tended to decrease, while the sen sitivity remained fairly stable. Overall, these findings suggest that a history of haematuria and/or visual haematuria are appropriate metho ds for preliminary screening of communities to identify those at risk of morbidity. Thereafter, microhaematuria (Ii positivity limit) may be the more appropriate method for targeting intervention at the individ ual level.