Gass Katherine M, Sime Heven, Mwingira Upendo J, Nshala Andreas, Chikawe Maria, Pelletreau Sonia, Barbre Kira A, Deming Michael S, Rebollo Maria P
Neglected Tropical Disease Support Center, Task Force for Global Health, Atlanta, United States of America.
Ethiopian Public Health Institute, Addis Ababa, Ethiopia.
PLoS Negl Trop Dis. 2017 Oct 4;11(10):e0005944. doi: 10.1371/journal.pntd.0005944. eCollection 2017 Oct.
Endemicity mapping is required to determining whether a district requires mass drug administration (MDA). Current guidelines for mapping LF require that two sites be selected per district and within each site a convenience sample of 100 adults be tested for antigenemia or microfilaremia. One or more confirmed positive tests in either site is interpreted as an indicator of potential transmission, prompting MDA at the district-level. While this mapping strategy has worked well in high-prevalence settings, imperfect diagnostics and the transmission potential of a single positive adult have raised concerns about the strategy's use in low-prevalence settings. In response to these limitations, a statistically rigorous confirmatory mapping strategy was designed as a complement to the current strategy when LF endemicity is uncertain. Under the new strategy, schools are selected by either systematic or cluster sampling, depending on population size, and within each selected school, children 9-14 years are sampled systematically. All selected children are tested and the number of positive results is compared against a critical value to determine, with known probabilities of error, whether the average prevalence of LF infection is likely below a threshold of 2%. This confirmatory mapping strategy was applied to 45 districts in Ethiopia and 10 in Tanzania, where initial mapping results were considered uncertain. In 42 Ethiopian districts, and all 10 of the Tanzanian districts, the number of antigenemic children was below the critical cutoff, suggesting that these districts do not require MDA. Only three Ethiopian districts exceeded the critical cutoff of positive results. Whereas the current World Health Organization guidelines would have recommended MDA in all 55 districts, the present results suggest that only three of these districts requires MDA. By avoiding unnecessary MDA in 52 districts, the confirmatory mapping strategy is estimated to have saved a total of $9,293,219.
流行病情制图对于确定一个地区是否需要开展群体药物治疗（MDA）至关重要。当前淋巴丝虫病（LF）的制图指南要求每个地区选择两个地点，在每个地点对100名成年人进行便利抽样，检测其是否存在抗原血症或微丝蚴血症。任一地点有一个或多个确诊阳性检测结果即被视为潜在传播的指标，从而促使在该地区开展群体药物治疗。虽然这种制图策略在高流行率地区效果良好，但诊断不完善以及单个阳性成年人的传播潜力引发了对该策略在低流行率地区应用的担忧。针对这些局限性，设计了一种统计严格的验证性制图策略，以便在淋巴丝虫病流行情况不确定时作为当前策略的补充。在新策略下，根据人口规模通过系统抽样或整群抽样选择学校，在每个选定的学校内，对9至14岁的儿童进行系统抽样。对所有选定的儿童进行检测，并将阳性结果的数量与临界值进行比较，以确定在已知误差概率的情况下，淋巴丝虫病感染的平均流行率是否可能低于2%的阈值。这种验证性制图策略应用于埃塞俄比亚的45个地区和坦桑尼亚的10个地区，这些地区的初步制图结果被认为不确定。在埃塞俄比亚的42个地区以及坦桑尼亚所有10个地区，抗原血症儿童的数量低于临界值，这表明这些地区不需要开展群体药物治疗。只有三个埃塞俄比亚地区超过了阳性结果的临界值。按照世界卫生组织目前的指南，原本会建议在所有55个地区开展群体药物治疗，但目前的结果表明，这些地区中只有三个需要开展群体药物治疗。通过避免在52个地区进行不必要的群体药物治疗，据估计验证性制图策略总共节省了9,293,219美元。
