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

Lau, Colleen L., Sheel, Meru, Gass, Katherine, Fuimaono, Saipale, David, Michael C., Won, Kimberly Y., Sheridan, Sarah, and Graves, Patricia M. (2020) 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. PLoS Neglected Tropical Diseases, 14 (12). e0008916.

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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.

Item ID: 66304
Item Type: Article (Research - C1)
ISSN: 1935-2735
Copyright Information: This is an open access article, free of all copyright, and may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose. The work is made available under the Creative Commons CC0 public domain dedication.
Funders: Coalition for Operational Research on Neglected Tropical Diseases (CORNTD), Task Force for Global Health, Bill and Melinda Gates Foundation (BMGF), United States Agency for International Development (USAID), UKaid, Australian National Health and Medical Research Council (NHMRC), Westpac Scholars Trust
Projects and Grants: CORNTD OPP1053230, USAID Neglected Tropical Diseases Program, NHMRC 1109035
Date Deposited: 08 Mar 2021 05:19
FoR Codes: 42 HEALTH SCIENCES > 4202 Epidemiology > 420202 Disease surveillance @ 34%
45 INDIGENOUS STUDIES > 4516 Pacific Peoples health and wellbeing > 451605 Pacific Peoples epidemiology @ 33%
32 BIOMEDICAL AND CLINICAL SCIENCES > 3207 Medical microbiology > 320704 Medical parasitology @ 33%
SEO Codes: 20 HEALTH > 2003 Provision of health and support services > 200303 Health surveillance @ 50%
20 HEALTH > 2005 Specific population health (excl. Indigenous health) > 200599 Specific population health (excl. Indigenous health) not elsewhere classified @ 50%
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