In 2000, the American Samoa Department of Health initiated a campaign of annual mass drug administration (MDA) with albendazole and diethylcarbamazine (DEC) to eliminate transmission of filariasis. Drug coverage was well below prescribed targets in the first three campaigns, ranging from 24 to 52% of the total population. Evaluation findings from a variety of formative research methods identified opportunities to improve MDA coverage and ensuing program modifications resulted in increased drug coverage of 65-71% in the following four annual distributions. Partnering with churches for drug distribution and using multiple media channels for health promotion led to sustained program improvements. With the increased emphasis on the use of mass distribution for delivery of drugs for a number of neglected tropical diseases, other programs may benefit from a similar approach.

Assessing the interruption of lymphatic filariasis transmission after annual mass drug administration (MDA) requires a better understanding of how to interpret results obtained with the available diagnostic tools. We conducted parasitologic, serologic, and entomologic surveys in three villages in American Samoa after sentinel site surveys suggested filarial antigen prevalence was < 1% after five annual MDAs with diethylcarbamazine and albendazole. Antigen and antifilarial antibody prevalence ranged from 3.7% to 4.6% and from 12.5% to 14.9%, respectively, by village. Only one person was microfilaria positive. Although no children less than 10 years of age were antigen positive, antifilarial antibody prevalence in this age group was 5.1% and antibody-positive children were detected in all three villages. Wuchereria bancrofti-infected mosquitoes were also detected in all three villages. Thus, monitoring of infections in mosquitoes and antifilarial antibody levels in children may serve as indicators of local transmission and be useful for making decisions about program endpoints.

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.

American Samoa began a territory-wide mass drug administration (MDA) program with diethylcarbamazine and albendazole in 2000 after baseline surveys indicated that 16.5% of 2,989 residents were infected with Wuchereria bancrofti based on tests for circulating filarial antigen. Follow-up surveys were conducted in 2001, 2003, and 2006, using convenience samples of residents of sentinel villages. Antigenemia prevalence in 2001 (11.5%) and 2003 (13.5%) showed no change. After the 2003 sentinel assessment, improvements were made in the social mobilization and drug distribution strategies. In 2006, after a total of 5 years of MDA and 3 years of improved MDA participation, the antigenemia prevalence dropped from 11.5% (2001) to 0.95% (2006) (P < 0.0001). In 2006, antigenemia prevalence was greater in males (1.5%) than females (0.4%) (P = 0.04). The decline in antigenemia prevalence shows the effectiveness of MDA and changes made in social mobilization and drug distribution.