# Field evaluation of Standard Q Filariasis Antigen Test for Lymphatic Filariasis (LF) during a pre-transmission assessment survey in Sierra Leone, 2022

## TL;DR

A new diagnostic test for lymphatic filariasis was evaluated in Sierra Leone and found to be as effective as the current standard test.

## Contribution

The study confirms the SD Biosensor STANDARD Q Filariasis Antigen Test as a reliable and user-friendly alternative to the existing diagnostic tool in field conditions.

## Key findings

- QFAT had zero invalid tests in field conditions, unlike the FTS which had six invalid tests.
- The concordance between QFAT and FTS was 0.81, with no statistically significant difference in positive test results.
- QFAT is a credible diagnostic tool for Wuchereria bancrofti infection when compared to the FTS.

## Abstract

As part of a multi-country evaluation, the SD Biosensor STANDARD Q Filariasis Antigen Test (QFAT) was compared with the Abbott Bioline Filariasis Test Strip (FTS) for assessing Wuchereria bancrofti infection prevalence and for ease of use of QFAT in field conditions in Sierra Leone.

The evaluation was done in two districts, Bombali and Karene, where repeat pre-transmission assessment surveys (pre-TAS) were planned. Two rural sites, Kagbo and Makorba Yelimini which recorded high LF antigen prevalence of 4.1% and 7.7% respectively in repeat pre-TAS in 2020 were selected for the QFAT evaluation. At least 350 people ≥5 years were targeted per site for inclusion in the study by convenience sampling. Blood was collected by fingerstick; 20μl for QFAT and 75μl for FTS. The reading time for both tests was 10 minutes. For all positive or invalid results, a repeat test was performed for both tests. In total, 728 participants (5–91 years) were tested by QFAT and FTS. Four FTS and three QFAT final results were classified as indeterminate (meaning a positive result followed by a negative result) and were excluded from the analysis. The positive rate was 4.8% (17/357) and 3.5% (13/367) for FTS and 3.4% (12/359) and 4.1% (15/366) for QFAT in Kagbo and Makorba Yelimi, respectively. All participants testing positive for FTS or QFAT underwent further testing by night blood smear to detect microfilariae using microscopy. No W. bancrofti microfilariae was detected in any of the antigen positive cases. In field conditions, QFAT was easy to handle and recorded zero invalid tests compared to FTS (six invalids). The concordance between FTS and QFAT was 0.81 (Cohen’s Kappa). The discrepancy found between the two tests in terms of positive tests was not statistically significant (p = 0.78).

The results suggest that the QFAT is a credible W. bancrofti diagnostic test when compared to the routinely used FTS; use of either test would result in the same program decision.

Lymphatic filariasis (LF) is a vector-borne disease targeted for elimination as a public health problem by 2030. The Global Program to Eliminate LF recommends tools to measure the impact of interventions on infection prevalence and when elimination has been achieved. A reliable and easy to use diagnostic tool is key for the success of the global program. Currently only one rapid antigen test is used for programs in Wuchereria bancrofti endemic countries. This study was part of a multi-country field evaluation of a new W. bancrofti antigen lateral flow assay rapid diagnostic test, the SD Biosensor STANDARDQ Filarial Antigen Test (QFAT). The primary objective was to determine comparability of QFAT to the Abbott Bioline Filariasis Test Strip (FTS) in its ability to classify LF prevalence at a population level and compare performance of QFAT to FTS. In addition, information was collected on the ease of use of QFAT in field settings. The evaluation was done in two districts (Bombali and Karene) in Serra Leone, which were undergoing repeat pre-transmission assessment surveys (pre-TAS). The results of the study confirm QFAT as a suitable alternative to the currently recommended FTS. In field conditions, using QFAT seems effective given that no invalid test was recorded compared to six invalid FTS tests.