Elimination within reach: A cross-sectional study highlighting the factors that contribute to persistent lymphatic filariasis in eight communities in rural Ghana

Background
Despite the progress achieved in scaling-up mass drug administration (MDA) for lymphatic filariasis (LF) in Ghana, communities with persistent LF still exist even after 10 years of community treatment. To understand the reasons for persistence, we conducted a study to assess the status of disease elimination and understand the adherence to interventions including MDA and insecticide treated nets.
Methodology and principal findings
We conducted a parasitological and epidemiological cross-sectional study in adults from eight villages still under MDA in the Northern Region savannah and the coastal Western Region of the country. Prevalence of filarial antigen ranged 0 to 32.4% and in five villages the prevalence of night blood microfilaria (mf) was above 1%, ranging from 0 to 5.7%. Median mf density was 67 mf/ml (range: 10–3,560). LF antigen positivity was positively associated with male sex but negatively associated with participating in MDA the previous year. Male sex was also associated with a decreased probability of participating in MDA. A stochastic model (TRANSFIL) was used to assess the expected microfilaria prevalence under different MDA coverage scenarios using historical data on one community in the Western Region. In this example, the model simulations suggested that the slow decline in mf prevalence is what we would expect given high baseline prevalence and a high correlation between MDA adherence from year to year, despite high MDA coverage.
Conclusions
There is a need for an integrated quantitative and qualitative research approach to identify the variations in prevalence, associated risk factors and intervention coverage and use levels between and within regions and districts. Such knowledge will help target resources and enhance surveillance to the communities most at risk and to reach the 2020 LF elimination goals in Ghana.

背景
尽管加纳在淋巴丝虫病（lymphatic filariasis, LF）群体药物治疗（mass drug administration, MDA）规模化推广方面已取得显著进展，但即便经过10年的社区治疗，仍有部分社区存在淋巴丝虫病持续流行的情况。为探究流行持续的原因，本研究开展相关调查，以评估疾病消除现状，并了解民众对包括群体药物治疗与经杀虫剂处理蚊帐在内的干预措施的依从性。

研究方法与主要结果
本研究在该国北部地区稀树草原带与西部沿海地区的8个仍在开展群体药物治疗的村庄中，针对成年人群开展了寄生虫学与流行病学横断面调查。丝虫抗原阳性率介于0至32.4%之间，其中5个村庄的夜间血微丝蚴（microfilaria, mf）阳性率超过1%，区间为0至5.7%。微丝蚴密度的中位数为67条/ml，范围为10至3560条/ml。丝虫抗原阳性与男性性别呈正相关，但与前一年参与群体药物治疗呈负相关；男性性别同时与参与群体药物治疗的概率降低相关。研究针对西部沿海地区某社区的历史数据，采用随机模型（TRANSFIL）评估不同群体药物治疗覆盖场景下的预期微丝蚴阳性率。在此案例中，模型模拟结果显示：尽管群体药物治疗覆盖率较高，但鉴于基线阳性率较高且各年度群体药物治疗依从性相关性较强，微丝蚴阳性率的缓慢下降符合预期。

结论
有必要采用定量与定性相结合的研究方法，以明确各区域及行政区之间、内部的流行率差异、相关危险因素以及干预措施覆盖与使用水平。此类研究结果将有助于优化资源配置，加强对高风险社区的监测工作，助力加纳实现2020年淋巴丝虫病消除目标。