Field comparison of STANDARDTM Q Filariasis Antigen Test (QFAT) with Bioline Filariasis Test Strip (FTS) for the detection of Lymphatic Filariasis in Samoa, 2023

BackgroundTo monitor the progress of lymphatic filariasis (LF) elimination programmes, field surveys to assess filarial antigen (Ag) prevalence require access to reliable, user-friendly rapid diagnostic tests. We aimed to evaluate the performance of the new Q Filariasis Antigen Test (QFAT) with the currently recommended Filariasis Test Strip (FTS) for detecting the Ag of Wuchereria bancrofti, the causative agent of LF, under field conditions. Methodology/Principal FindingsDuring an LF survey in Samoa, 344 finger-prick blood samples were tested using FTS and QFAT. Microfilariae (Mf) status was determined from blood slides prepared from Ag-positive samples. Each test was re-read at 1 hour and the next day to determine the stability of results over time. Overall Ag-positivity by FTS was 29% and 30% by QFAT. Concordance between the two tests was 94% (Kappa=0.85). Of the 105 Mf slides available, 38.1% were Mf-positive, and all were Ag-positive by both tests. Darker test line intensities from Ag-positive FTS were found to predict Mf-positivity (compared to same/lighter line intensities). QFAT had significantly higher reported test result changes than FTS, mostly reported the next day. The field laboratory team preferred QFAT over FTS due to the smaller blood volume required, better usability, and easier readability. Conclusion/SignificanceQFAT could be a suitable and user-friendly diagnostic alternative for use in the monitoring and surveillance of LF in field surveys based on its similar performance to FTS under field conditions. Author SummaryLymphatic filariasis (LF) is a debilitating tropical disease caused by an infection with parasitic filarial worms that are transmitted by mosquitoes. Long-term infection can lead to stigmatising chronic conditions like lymphoedema and elephantiasis. The World Health Organization initiated the global programme to eliminate lymphatic filariasis (GPELF) in 2000, which focuses on the mass administration of anti-LF drugs to stop transmission in endemic countries. However, to monitor the success of this programme and to make informed decisions to stop costly mass drug administrations, it is crucial to have access to accurate and reliable rapid diagnostics. Here, we evaluated the performance of a new rapid antigen test called the Q Filariasis antigen test and compared it to the currently recommended filariasis test strip under field conditions in Samoa. This study showed that the new rapid test could be a suitable alternative to the currently recommended test for use in GPELF-related activities with more user-friendly features.