Diagnostic comparison of Baermann funnel, Koga agar plate culture and polymerase chain reaction for detection of human Strongyloides stercoralis infection in Maluku, Indonesia

Human infection with the nematode Strongyloides stercoralis, which may have a life-threatening course, primarily occurs in tropical settings. Epidemiological data on the occurrence of strongyloidiasis are scarce, and microscopic stool-based detection methods are insensitive. Polymerase chain reaction (PCR) assays have been developed, yet conflicting results have been reported. Our goal was to determine whether there was diagnostic agreement between an in-house PCR and two microscopic techniques, the Baermann funnel (BM) and the Koga agar plate culture (KAP) for the detection of S. stercoralis in stool samples. Eighty ethanol-fixed stool samples stemming from a cross-sectional survey in Maluku, Indonesia, were purposefully selected for PCR analysis. The final sample size comprised four groups, each with 20 samples: group 1, positive for S. stercoralis on both BM and KAP; group 2, positive only by BM; group 3, positive only by KAP; and group 4, negative on both BM and KAP. A Strongyloides-specific PCR targeting the internal transcribed spacer 2 (ITS2) region was carried out in an Indonesian reference laboratory. The overall agreement between PCR and microscopy was 61% (49/80 samples), being highest in group 1 (15/20, 75%) and lowest in group 3 (9/20, 45%). PCR revealed eight additional S. stercoralis infections in group 4. Future studies should elucidate the 'true' infection status of samples that are negative by PCR, but positive upon microscopy. Taken together, there is a lack of agreement between microscopy and PCR results for the diagnosis of human S. stercoralis infection in Indonesia.