Potential strategies for strengthening surveillance of lymphatic filariasis in American Samoa after mass drug administration: Reducing ‘number needed to test’ by targeting older age groups, hotspots, and household members of infected persons

Abstract

Under the Global Programme to Eliminate Lymphatic Filariasis (LF), American Samoa conducted mass drug administration (MDA) from 2000–2006. Despite passing Transmission Assessment Surveys (TAS) in 2011/2012 and 2015, American Samoa failed TAS-3 in 2016, with antigen (Ag) prevalence of 0.7% (95%CI 0.3–1.8%) in 6–7 year-olds. A 2016 community survey (Ag prevalence 6.2% (95%CI 4.4–8.5%) in age ≥8 years) confirmed resurgence. Using data from the 2016 survey, this study aims to i) investigate antibody prevalence in TAS-3 and the community survey, ii) identify risk factors associated with being seropositive for Ag and anti-filarial antibodies, and iii) compare the efficiency of different sampling strategies for identifying seropositive persons in the post-MDA setting. Antibody prevalence in TAS-3 (n = 1143) were 1.6% for Bm14 (95%CI 0.9–2.9%), 7.9% for Wb123 (95%CI 6.4–9.6%), and 20.2% for Bm33 (95%CI 16.7–24.3%); and in the community survey (n = 2507), 13.9% for Bm14 (95%CI 11.2–17.2%), 27.9% for Wb123 (95%CI 24.6–31.4%), and 47.3% for Bm33 (95%CI 42.1–52.6%). Multivariable logistic regression was used to identify risk factors for being seropositive for Ag and antibodies. Higher Ag prevalence was found in males (adjusted odds ratio [aOR] 3.01), age ≥18 years (aOR 2.18), residents of Fagali’i (aOR 15.81), and outdoor workers (aOR 2.61). Ag prevalence was 20.7% (95%CI 9.7–53.5%) in households of Ag-positive children identified in TAS-3. We used NNTestav (average number needed to test to identify one positive) to compare the efficiency of the following strategies for identifying persons who were seropositive for Ag and each antibody: i) TAS of 6–7 year-old children, ii) population representative surveys of older age groups, and iii) targeted surveillance of subpopulations at higher risk of being seropositive (older ages, householders of Ag-positive TAS children, and known hotspots). For Ag, NNTestav ranged from 142.5 for TAS, to <5 for households of index children. NNTestav was lower in older ages, and highest for Ag, followed by Bm14, Wb123 and Bm33 antibodies. We propose a multi-stage surveillance strategy, starting with population-representative sampling (e.g. TAS or population representative survey of older ages), followed by strategies that target subpopulations and/or locations with low NNTestav. This approach could potentially improve the efficiency of identifying remaining infected persons and residual hotspots. Surveillance programs should also explore the utility of antibodies as indicators of transmission.

Uji Diagnostik Filariasis Menggunakan Rapid Diagnostic Test (RDT) Brugia malayi terhadap Pemeriksaan Mikroskopis di Desa Buntoi Kabupaten Gunung Mas, Provinsi Kalimantan Tengah

“…13 Studi di beberapa negara seperti Ghana, Fiji, Samoa Amerika, dan Myanmar menunjukkan bahwa prevalensi Mf rate mengalami penurunan setelah kegiatan MDA. [14][15][16][17] Hal sama di Pulau Flores Indonesia, menunjukkan adanya MDA dapat mengurangi prevalensi mikrofilaria menjadi kurang dari 1% di daerah dengan prevalensi awal yang rendah hingga sedang. 18 Hasil uji diagnostik pemeriksaan RDT B. malayi terhadap pemeriksaan mikroskopis SDJ menunjukkan nilai sensitifitas 0%, nilai spesivitas 100%, nilai NPV 0%, dan nilai PPV 100%.…”

Potential use of antibodies to provide an earlier indication of lymphatic filariasis resurgence in post-mass drug administration surveillance, American Samoa

“…Ag prevalence declines after the implementation of MDA, and as prevalence drops to low levels, more accurate tests and surveillance methods will be required to detect transmission signals. TAS currently relies on Ag test results only, and antigenemia alone may not be sensitive enough to ensure timely detection of ongoing transmission or recrudescence (Lau et al, 2020). Existing evidence suggests that Ab responses may provide an earlier indicator of filarial infection than Ag (Joseph H et al, 2011).…”

“…One of the strategies proposed by GPELF focused on interrupting transmission by implementing mass drug administration (MDA) of antifilarial drugs in endemic areas (World Health Organization, 2000). A key challenge faced by most LF-endemic countries that have implemented MDA is to effectively undertake post-validation surveillance (Lau et al, 2020).…”

“…In the first three years, population coverage by MDA was 24-52% and improved to 65-71% in the subsequent four years (World Health Organization, 2006). American Samoa passed TAS-1 (in February 2011) and TAS-2 (in April 2015) with numbers of Ag-positive children below the critical cut-off of six (two Ag-positive children in TAS-1 and one Ag-positive child in TAS-2, equivalent to crude prevalence of 0.2% (95% CI 0.0 to 0.8%), and 0.1% (95% CI 0.0 to 0.7%), respectively (Won Kimberly Y. et al, 2018). However, the territory failed TAS-3 in November 2016, with nine Ag-positive children, an adjusted prevalence of 0.7% (95% CI 0.3 to 1.8%), higher than the cut-off and the recommended upper confidence limit of 1% (Sheel et al, 2018).…”

“…Existing evidence suggests that Ab responses may provide an earlier indicator of filarial infection than Ag (Joseph H et al, 2011). While the development and duration of serological responses to specific anti-filarial Abs such as Bm14, Bm33 and Wb123 are poorly understood, Ab testing may have a potential role in post-MDA and post-validation surveillance in W. bancrofti -endemic areas (Won Kimberly Y et al, 2018).…”