Time Series Analysis of Onchocerciasis Data from Mexico: A Trend towards Elimination

BackgroundIn Latin America, there are 13 geographically isolated endemic foci distributed among Mexico, Guatemala, Colombia, Venezuela, Brazil and Ecuador. The communities of the three endemic foci found within Mexico have been receiving ivermectin treatment since 1989. In this study, we predicted the trend of occurrence of cases in Mexico by applying time series analysis to monthly onchocerciasis data reported by the Mexican Secretariat of Health between 1988 and 2011 using the software R. ResultsA total of 15,584 cases were reported in Mexico from 1988 to 2011. The data of onchocerciasis cases are mainly from the main endemic foci of Chiapas and Oaxaca. The last case in Oaxaca was reported in 1998, but new cases were reported in the Chiapas foci up to 2011. Time series analysis performed for the foci in Mexico showed a decreasing trend of the disease over time. The best-fitted models with the smallest Akaike Information Criterion (AIC) were Auto-Regressive Integrated Moving Average (ARIMA) models, which were used to predict the tendency of onchocerciasis cases for two years ahead. According to the ARIMA models predictions, the cases in very low number (below 1) are expected for the disease between 2012 and 2013 in Chiapas, the last endemic region in Mexico. ConclusionThe endemic regions of Mexico evolved from high onchocerciasis-endemic states to the interruption of transmission due to the strategies followed by the MSH, based on treatment with ivermectin. The extremely low level of expected cases as predicted by ARIMA models for the next two years suggest that the onchocerciasis is being eliminated in Mexico. To our knowledge, it is the first study utilizing time series for predicting case dynamics of onchocerciasis, which could be used as a benchmark during monitoring and post-treatment surveillance.背景：在拉丁美洲，墨西哥、危地马拉、哥伦比亚、委内瑞拉、巴西及厄瓜多尔境内分布着13个地理隔离的地方性盘尾丝虫病（onchocerciasis）疫源地。其中墨西哥境内的3个地方性疫源地所在社区自1989年起便开始接受伊维菌素（ivermectin）治疗。本研究借助R软件，对1988年至2011年墨西哥卫生秘书处（Mexican Secretariat of Health, MSH）报告的月度盘尾丝虫病数据开展时间序列分析，以此预测墨西哥的病例发生趋势。 结果：1988年至2011年，墨西哥累计报告盘尾丝虫病病例15584例，相关数据主要来自恰帕斯州与瓦哈卡州的主要地方性疫源地。瓦哈卡州最后一例病例报告于1998年，而恰帕斯疫源地直至2011年仍有新发病例报告。针对墨西哥境内疫源地的时间序列分析显示，该病的发生随时间呈下降趋势。赤池信息准则（Akaike Information Criterion, AIC）最小的最优拟合模型为自回归积分滑动平均（Auto-Regressive Integrated Moving Average, ARIMA）模型，本研究利用该模型对未来两年的盘尾丝虫病病例趋势进行了预测。根据ARIMA模型的预测结果，2012年至2013年，墨西哥最后一个地方性疫源地恰帕斯州的盘尾丝虫病病例数将极低（低于1例）。 结论：依托墨西哥卫生秘书处推行的伊维菌素治疗策略，墨西哥的盘尾丝虫病地方性流行区已从高流行状态实现传播中断。ARIMA模型预测的未来两年极低病例数表明，墨西哥正在消除盘尾丝虫病。据我们所知，本研究是首个利用时间序列分析预测盘尾丝虫病病例动态的研究，可作为监测与治疗后监测工作的基准参考。