Abstract
Circulating filarial antigen (Ag) prevalence, measured using rapid point-of-care tests, is the standard indicator used for monitoring and surveillance in the Global Program to Eliminate Lymphatic Filariasis. In 2015, the immunochromatographic test (ICT) was replaced with the filariasis test strip (FTS), which has higher reported sensitivity. Despite differences in sensitivity, no changes in recommended surveillance targets were made when the FTS was introduced. In 2016, we conducted lymphatic filariasis surveys in American Samoa using FTS, which found higher Ag prevalence than previous surveys that used ICT. To determine whether the increase was real, we assessed the concordance between FTS and ICT results by paired testing of heparinised blood from 179 individuals (63% FTS-positive). ICT had 93.8% sensitivity and 100% specificity for identifying FTS-positive persons, and sensitivity was not associated with age, gender, or presence of microfilariae. Based on these findings, if ICT had been used in the 2016 surveys, the results and interpretation would have been similar to those reported using FTS. American Samoa would have failed Transmission Assessment Survey (TAS) of Grade 1 and 2 children with either test, and community prevalence would not have been significantly different (4.1%, 95% CI, 3.3–4.9% with FTS vs. predicted 3.8%, 95%, CI: 3.1–4.6% with ICT).
Highlights
filariasis test strip (FTS) identified more Ag-positive (112/179, 62.6%, 95% confidence intervals (CI): 55.0–69.7%) persons compared with immunochromatographic test (ICT) (105/179, 58.7%, 95% CI: 51.1–65.9%) but the difference in estimated overall prevalence was not statistically significant (p > 0.05)
If we apply the same assumptions about test characteristics to the 2016 community survey, we would have found similar crude Ag prevalence of 3.8% (CI 3.1–4.6%) using ICT compared with 4.1% (CI 3.3–4.9%) using FTS. In this 2016 study, we present findings comparing FTS and ICT in American Samoa in a post-mass drug administration (MDA) setting
The results show that ICT had lower sensitivity (93.8%) than but the same specificity (100%) as FTS
Summary
It is estimated that 893 million people living in 49 countries continue to be at risk of LF and require preventive chemotherapy to stop the spread of this parasitic infection [1]. The Global Programme to Eliminate Lymphatic Filariasis (GPELF), launched by the World Health Organization (WHO) in 2000, aims to interrupt LF transmission by conducting mass drug administration (MDA) in all endemic countries and providing morbidity management and disability prevention for those infected. In 2019, GPELF reported that 72 countries were LF-endemic based on progress in MDA and validation of elimination status [2]. In the WHO Western Pacific Region, the Pacific Programme to Eliminate LF (PacELF) supported 22 Pacific Island Countries and Territories. As of 2019, Cook Islands, Kiribati, Niue, the Marshall Islands, Tonga and Vanuatu have been validated by WHO for successfully achieving elimination targets [2]
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