Laboratory Comparison of Rapid Antigen Diagnostic Tests for Lymphatic Filariasis: STANDARDTMQ Filariasis Antigen Test (QFAT) and Bioline Filariasis Test Strip (FTS)
Authors: Graves Patricia M , Scott Jessica L , Soto Alvaro Berg , Widi Antin YN , Whittaker Maxine , Lee Derek , Lau Colleen L , Won Kimberly Y 
Published: March 2024

Background

Accurate and user-friendly rapid diagnostic tests (RDT) are needed to assess prevalence ofWuchereria bancroftiantigen in the Global Programme to Eliminate Lymphatic Filariasis (GPELF). We evaluated performance under laboratory conditions of the new Q Filariasis Antigen Test (QFAT) against the Filariasis Test Strip (FTS) for detecting antigen ofWuchereria bancrofti, a causative agent of lymphatic filariasis (LF).

Methodology/Principal Findings: We compared test performance using available panels of serum (n=195) and plasma (n=189) from LF endemic areas in the Asia-Pacific region (Samoa, American Samoa and Myanmar) together with Australian negative controls (n=46). Prior antigen and antibody positivity status of endemic samples had been determined by rapid test or ELISA. The proportion of all samples testing positive at 10 minutes was higher with QFAT (44.8%) than FTS (41.3%).

Concordance between tests was 93.5% (kappa 0.87, N=417) at 10 minutes, and increased over time to 98.8% (kappa 0.98) at 24 hours. Sensitivity of QFAT and FTS at 10 minutes compared to prior antigen results were 92% (95% CI 88.0-96.0) and 86% (95% CI 80.0-90.0), respectively. Specificity was 98% for QFAT and 99% for FTS at 10 minutes. Sensitivity increased over time for both tests, rising to 99% for QFAT and 97% for FTS at 24 hours. QFAT positively identified all microfilaria (Mf)-positive samples, whereas FTS was negative for 3 of 66 Mf-positives. For both QFAT and FTS, there was evidence of cross-reaction withDirofilaria repensandOnchocerca lupibut not withAcanthochilonema reconditum,Cercopithifilaria bainae or Strongyloides.Disadvantages noted for QFAT were inconvenient packaging and an additional buffer step. Advantages of QFAT include ease-of-use, smaller sample (10-20 µL vs 75 µL for FTS), clearer control line, and higher sensitivity for Mf-positive samples.

Conclusions/Significance. Under lab conditions, QFAT is a suitable rapid Ag test for use in filariasis elimination programmes and has advantages over FTS.

Author summary

Lymphatic filariasis (LF) is a debilitating and stigmatizing disease that affects populations in tropical areas usually in developing social environments. It is caused by a parasite worm transmitted by mosquitoes. The WHO programme to eliminate LF aims to improve the lives of their residents through a global mass drug administration campaign, and provide the tools to monitor prevalence within the countries’ public health contexts. It is imperative to utilize the most effective and practical diagnostic tests to monitor progress to elimination of this disease, while ensuring a cost-effective and rapid implementation under potentially vulnerable settings. In this study we investigated the performance of a new rapid antigen diagnostic test for LF compared to the existing recommended test, in samples of known infection status from the Asia-Pacific region. The results showed the new test to be a suitable rapid antigen test, with advantages over the current test, for use in filariasis elimination programmes in the region.