Enhanced detection of Opisthorchis viverrini infection: A comparative evaluation of modified one-step FECT and conventional diagnostic methods in low-intensity setting

The formalin-ethyl acetate concentration technique (FECT) is one of the most sensitive diagnostic method not only for all helminths, but also for <i>Opisthorchis viverrini</i> infections in stool examinations. However, it remains a diagnostic problem for light infections. We modified the one-step FECT to determine the low-intensity of <i>O. viverrini</i> infection and compared with various conventional detection methods. The study utilized 160 egg-positive and 160 randomly negative stool samples for <i>O. viverrini</i> eggs by conventional FECT (cFECT) to compare the methods, including the simple smear, the Kato-Katz method, the two commercial stool examination kits, and the one-step FECT. Our results showed that the one-step FECT method had the highest sensitivity (95.6 %), followed by cFECT (87.9 %), the Kato-Katz (55.5 %), Aquisfek SF-FIX® (48.3 %), simple smear (42.3 %), and Mini Parasep® SF (35.1 %). The ability of one-step FECT exhibited better ability to detect low parasite intensities compared to the cFECT (18 eggs per gram (e.p.g.) versus 34 e.p.g.) and the other conventional diagnostic methods. In addition, the investigation of <i>O. viverrini</i> infection in endemic regions in northeastern Thailand based on 3900 fecal samples revealed that the one-step FECT with an intensity of 66.8 e.p.g. (range 18-226) was significantly higher in sensitivity than cFECT, which had an intensity of 58.0 e.p.g. (range 34-214). Interestingly, fecal samples with less than 50 e.p.g. could not be detected by cFECT in 67 % of cases, and 69 out of 3900 samples were negative. In conclusion, one-step FECT improves the detection of low-intensity <i>O. viverrini</i> infection, which is suitable for parasites screening, especially for low-intensity infections in the community.