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 Negl Trop Dis. 2020 Dec 28;14(12):e0008916. doi: 10.1371/journal.pntd.0008916. eCollection 2020 Dec.

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.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Adolescent
  • Adult
  • Age Factors
  • American Samoa / epidemiology
  • Animals
  • Antibodies, Helminth / blood
  • Child
  • Child, Preschool
  • Elephantiasis, Filarial / epidemiology*
  • Elephantiasis, Filarial / transmission*
  • Epidemiological Monitoring*
  • Female
  • Humans
  • Infant
  • Male
  • Mass Screening / methods*
  • Prevalence
  • Residence Characteristics
  • Sample Size
  • Wuchereria bancrofti / isolation & purification

Substances

  • Antibodies, Helminth

Grants and funding

This work received financial support from the Coalition for Operational Research on Neglected Tropical Diseases (https://www.ntdsupport.org/cor-ntd), which is funded at The Task Force for Global Health primarily by the Bill & Melinda Gates Foundation [Grant number OPP1053230], by the United States Agency for International Development through its Neglected Tropical Diseases Program, and with UK aid from the British people. KG was an employee of The Task Force for Global Health. CLL was supported by an Australian National Health and Medical Research Council (www.nhmrc.gov.au) Fellowship (Grant number 1109035). MS was supported by a fellowship funded by the Westpac Scholars Trust. Other than KG who was an employee of The Task Force for Global Health, the funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.