Prevalence and risk factors associated with lymphatic filariasis in American Samoa after mass drug administration

Abstract

BackgroundIn 2000, American Samoa had 16.5% prevalence of lymphatic filariasis (LF) antigenemia. Annual mass drug administration (MDA) was conducted using single-dose albendazole plus diethylcarbamazine from 2000 to 2006. This study presents the results of a 2007 population-based PacELF C-survey in all ages and compares the adult filarial antigenemia results of this survey to those of a subsequent 2010 survey in adults with the aim of improving understanding of LF transmission after MDA.ResultsThe 2007 C-survey used simple random sampling of households from a geolocated list. In 2007, the overall LF antigen prevalence by immunochromatographic card test (ICT) for all ages was 2.29% (95% CI 1.66–3.07). Microfilaremia prevalence was 0.27% (95% CI 0.09–0.62). Increasing age (OR 1.04 per year, 95% CI 1.02–1.05) was significantly associated with ICT positivity on multivariate analysis, while having ever taking MDA was protective (OR 0.39, 95% CI 0.16–0.96). The 2010 survey used a similar spatial sampling design.The overall adult filarial antigenemia prevalence remained relatively stable between the surveys at 3.32% (95% CI 2.44–4.51) by ICT in 2007 and 3.23 (95% CI 2.21–4.69) by Og4C3 antigen in 2010. However, there were changes in village-level prevalence. Eight village/village groupings had antigen-positive individuals identified in 2007 but not in 2010, while three villages/village groupings that had no antigen-positive individuals identified in 2007 had positive individuals identified in 2010.ConclusionsAfter 7 years of MDA, with four rounds achieving effective coverage, a representative household survey in 2007 showed a decline in prevalence from 16.5 to 2.3% in all ages. However, lack of further decline in adult prevalence by 2010 and fluctuation at the village level showed that overall antigenemia prevalence at a broader scale may not provide an accurate reflection of ongoing transmission at the village level.

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

“…Elimination of lymphatic filariasis as a public health problem is proving to be a challenge for GPELF in some countries. Despite MDA programmes [7] similar to those that successfully achieved validation of elimination in several PacELF countries, including Vanuatu [25], Niue [26] and Tonga [27], American Samoa has not yet achieved this milestone, even though prevalence fell to low levels by 2007 [10,28,29]. The processes for post-MDA surveillance and monitoring are not yet well defined, resource intensive and may fall by the wayside in the face of competing priorities.…”

“…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].…”

Potential strategies for strengthening surveillance of lymphatic filariasis in American Samoa after mass drug administration: targeting older age groups, hotspots, and household members of infected persons

“…NNTest av could be used as a summary measure to compare the conditional probabilities of identifying a positive test in subgroups, e.g. positive antigen in [6][7] year-old children who live in known LF hotspots vs positive antibody in adults in randomly selected villages.…”

Pengaruh Iklim Terhadap Peluang Umur Nyamuk Mansonia spp di Daerah Endemis Filariasis di Kabupaten Kapuas

“…15 Penularan filariasis dipengaruhi oleh beberapa faktor, diantaranya adanya penderita positif mikrofilaria, kepadatan vektor penular, perilaku masyarakat serta faktor ekologi yang mempengaruhi kepadatan vektor. 16,17…”