Control of Schistosoma haematobium morbidity on Pemba Island: validity and efficiency of indirect screening tests.

Four indirect screening methods for the detection of Schistosoma haematobium morbidity are compared (history of haematuria, visual haematuria, and microhaematuria at the 1+ and 2+ positivity limit by reagent strips) in terms of their diagnostic performance under conditions of progressive decrease in prevalence of infection, intensity and risk of morbidity as a result of repeated schistosomiasis control programmes on Pemba Island, United Republic of Tanzania. The results show that the sensitivity 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 haematuria had a higher specificity, positive predictive value, and efficiency than a history of haematuria in both children and adults. Microhaematuria 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 indirect methods tended to increase in specificity, negative predictive value, and efficiency during the course of the intervention programme. In contrast, positive predictive value tended to decrease, while the sensitivity remained fairly stable. Overall, these findings suggest that a history of haematuria and/or visual haematuria are appropriate methods for preliminary screening of communities to identify those at risk of morbidity. Thereafter, microhaematuria (1+ positivity limit) may be the more appropriate method for targeting intervention at the individual level.