Identifying residual transmission of lymphatic filariasis after mass drug administration: Comparing school-based versus community-based surveillance - American Samoa, 2016

Abstract

IntroductionUnder the Global Programme to Eliminate Lymphatic Filariasis (LF), American Samoa conducted seven rounds of mass drug administration (MDA) from 2000–2006. The World Health Organization recommends systematic post-MDA surveillance using Transmission Assessment Surveys (TAS) for epidemiological assessment of recent LF transmission. We compared the effectiveness of two survey designs for post-MDA surveillance: a school-based survey of children aged 6–7 years, and a community-based survey targeting people aged ≥8 years.MethodsIn 2016, we conducted a systematic school-based TAS in all elementary schools (N = 29) and a cluster survey in 28 villages on the two main islands of American Samoa. We collected information on demographics and risk factors for infection using electronic questionnaires, and recorded geo-locations of schools and households. Blood samples were collected to test for circulating filarial antigen (CFA) using the Alere Filariasis Test Strip. For those who tested positive, we prepared slides for microscopic examination of microfilaria and provided treatment. Descriptive statistics were performed for questionnaire variables. Data were weighted and adjusted to account for sampling design and sex for both surveys, and for age in the community survey.ResultsThe school-based TAS (n = 1143) identified nine antigen-positive children and found an overall adjusted CFA prevalence of 0.7% (95% CI: 0.3–1.8). Of the nine positive children, we identified one microfilariaemic 7-year-old child. The community-based survey (n = 2507, 711 households) identified 102 antigen-positive people, and estimated an overall adjusted CFA prevalence of 6.2% (95% CI: 4.5–8.6). Adjusted village-level prevalence ranged from 0–47.1%. CFA prevalence increased with age and was higher in males. Of 86 antigen-positive community members from whom slides were prepared, 22 (25.6%) were microfilaraemic. School-based TAS had limited sensitivity (range 0–23.8%) and negative predictive value (range 25–83.3%) but had high specificity (range 83.3–100%) and positive predictive value (range 0–100%) for identifying villages with ongoing transmission.ConclusionsAmerican Samoa failed the school-based TAS in 2016, and the community-based survey identified higher than expected numbers of antigen-positive people. School-based TAS was logistically simpler and enabled sampling of a larger proportion of the target population, but the results did not provide a good indication of the overall CFA prevalence in older age groups and was not sensitive at identifying foci of ongoing transmission. The community-based survey, although operationally more challenging, identified antigen-positive individuals of all ages, and foci of high antigen prevalence. Both surveys confirmed recrudescence of LF transmission.

Demographic, socioeconomic and disease knowledge factors, but not population mobility, associated with lymphatic filariasis infection in adult workers in American Samoa in 2014

“…It is not clear that the current recommendations for transmission assessment surveys (TAS) in 6-7 year-old children are sensitive enough to pick up resurgent transmission until prevalence has reached high levels, and/or when transmission has become widespread. After MDA stopped in 2006, no TAS were done in American Samoa until 2011, and although TAS-1 in 2011 and TAS-2 in 2015 officially 'passed' the WHO targets [9], the same was not true for TAS-3 in 2016 which showed prevalence had clearly increased [13], necessitating restarting MDA with three drugs in 2018.…”

“…Regarding age, our sample was working-age adults only (16-68 years), with 3-to 4-fold higher prevalence of Bm14 antibody in agegroups over 35. The increased prevalence of LF in males is frequently observed worldwide, including in American Samoa [10][11][12][13] but the reasons for it are not clear. Variable exposure (e.g.…”

“…A seroprevalence survey in American Samoa in 2000 demonstrated an antigen prevalence of 16.5% (using Binax Now, a precursor to Alere ICT), which had declined to 2.3% in 2007 after seven rounds of MDA [10]. However, transmission was not interrupted and new infections continued to occur in both children and adults, as shown by subsequent research surveys in 2010 [11], 2014 [12] and 2016 [13], and by TAS conducted as part of programmatic activities in 2011, 2015 and 2016 [9,13]. The persistent high prevalence in 2016, the presence of hotspots of transmission, and apparent resurgence of infection rates has led to the use of the new triple drug strategy (ivermectin, DEC and albendazole, or IDA), with the first round distributed in 2018.…”

Entomological Assessment in Tangerang, Indonesia: Post Transmission Assessment Survey of Lymphatic Filariasis Endemic Villages

“…A community-based survey in American Samoa has identified the existence of LF residual transmission where a number of people has higher number of positive antigen than expected. Sheel et al (2016) mentioned that schoolbased TAS was logistically simpler, and it is possible to acquire samples from a larger proportion than the target population. However, the result is not going to provide better indication than the total prevalence of CFA on the age beyond school age [11].…”

“…Sheel et al (2016) mentioned that schoolbased TAS was logistically simpler, and it is possible to acquire samples from a larger proportion than the target population. However, the result is not going to provide better indication than the total prevalence of CFA on the age beyond school age [11]. This study aimed to describe the post-TAS entomological condition of selected LF endemic sub-districts in Tangerang.…”