Schistosoma mansoni in schoolchildren in a Madagascan highland school assessed by PCR and sedimentation microscopy and Bayesian estimation of sensitivities and specificities

Abstract

Madagascar is an endemic area for schistosomiasis, but recent prevalence data are scarce. We investigated stool samples of 410 children aged 4-18 years from a combined primary and secondary school in a Madagascan highland village near Ambositra in order to assess the prevalence of Schistosoma mansoni using microscopy and real-time polymerase chain reaction (PCR). A high prevalence of S. mansoni of 77.1% was detected by PCR, while only 15.2% of microscopic examinations of sedimentation-enriched stools were positive. We estimated the sensitivity and specificity of stool sedimentation microscopy (19.7% and 98.8%) and of PCR (98.9% and 89.3%) using a Bayesian approach for two dependant tests in one population without a reference standard. Our Bayesian posterior estimate of the prevalence is 80.2%. Simple sedimentation technique misses about 4/5 of all PCR-confirmed infections and is insufficient to determine the prevalence of S. mansoni. A survey comparing PCR with a classical standard technique (KatoKatz) is desirable.

Keywords: Madagascar; Microscopy; PCR; Prevalence; Schistosomiasis; Sensitivity and specificity.