Diagnostic sensitivity of direct wet mount microscopy for soil-transmitted helminth infections in Jimma Town, Ethiopia

Introduction: Soil-transmitted helminthiasis (STH) remains a major public health problem in school children in Ethiopia. Although direct wet mount microscopy (DWMM) is the means to diagnose parasitic diseases in health care facilities in Ethiopia, it remains unclear what its diagnostic performance is for STH. Methodology: A cross-sectional study was performed in Jimma Town (Ethiopia) and included 600 children from 10 primary schools. The diagnostic sensitivity of DWMM was compared to a composite reference standard (CRS) consisting of Kato-Katz, McMaster and Mini-FLOTAC. We also explored the impact of intensity of infection (the highest faecal egg counts (FECs; expressed as eggs per gram of stool (EPG)) across the CRS) on the diagnostic sensitivity of DWMM. Results: Based on the CRS, there were 210 Ascaris (35.0%), 312 Trichuris (52.0%) and 102 hookworm cases (17.0%). The median intensity of infections equalled 2,057 EPG for Ascaris, 200 EPG for Trichuris and 110 EPG for hookworms. The sensitivity of DWMM was 73.8% for Ascaris, but was around 17% for both Trichuris and hookworms. The sensitivity significantly increased with intensity of STH. For Ascaris, the odds for detecting an infection intensity of 1,000 EPG was 6.2 times higher than detecting an infection of 100 EPG. For Trichuris and hookworms, these odds ratios were 7.1 and 14. Conclusions: The diagnostic sensitivity of DWMM is low for STH, but it is able to detect those subjects that are in the highest need of treatment, and hence contributes to the global goal to eliminate STH as a public health problem