Low Sensitivity of the Formol-Ethyl Acetate Sedimentation Concentration Technique in Low-Intensity Schistosoma japonicum Infections

BACKGROUND: The endemic countries are in a diagnostic dilemma concerning Schistosoma japonicum with increasing difficulties in diagnosing the infected individuals. The formol-ethyl acetate sedimentation concentration technique is preferred by many clinical microbiology laboratories for the detection of parasites in stool samples. It is potentially more sensitive than the diagnostic methods traditionally used. METHODOLOGY/PRINCIPAL FINDINGS: We evaluated the technique for detection of low-intensity S. japonicum infections in 106 stool samples from China and used a commercial kit, Parasep Midi Faecal Parasite Concentrator. One stool sample and one serum sample were collected from each person. As reference standard we used persons positive by indirect hemagglutination in serum and positive by Kato-Katz thick smear microscopy (three slides from a single stool), and/or the hatching test. We found the sedimentation technique to have a sensitivity of only 28.6% and specificity of 97.4%. CONCLUSION/SIGNIFICANCE: This study indicates that the sedimentation technique has little to offer in the diagnosis of low-intensity S. japonicum infections, at least when only a single stool sample is examined.