A World Malaria Map: Plasmodium falciparum Endemicity in 2007

BackgroundEfficient allocation of resources to intervene against malaria requires a detailed understanding of the contemporary spatial distribution of malaria risk. It is exactly 40 y since the last global map of malaria endemicity was published. This paper describes the generation of a new world map of Plasmodium falciparum malaria endemicity for the year 2007. Methods and FindingsA total of 8,938 P. falciparum parasite rate (PfPR) surveys were identified using a variety of exhaustive search strategies. Of these, 7,953 passed strict data fidelity tests for inclusion into a global database of PfPR data, age-standardized to 2�C10 y for endemicity mapping. A model-based geostatistical procedure was used to create a continuous surface of malaria endemicity within previously defined stable spatial limits of P. falciparum transmission. These procedures were implemented within a Bayesian statistical framework so that the uncertainty of these predictions could be evaluated robustly. The uncertainty was expressed as the probability of predicting correctly one of three endemicity classes; previously stratified to be an informative guide for malaria control. Population at risk estimates, adjusted for the transmission modifying effects of urbanization in Africa, were then derived with reference to human population surfaces in 2007. Of the 1.38 billion people at risk of stable P. falciparum malaria, 0.69 billion were found in Central and South East Asia (CSE Asia), 0.66 billion in Africa, Yemen, and Saudi Arabia (Africa+), and 0.04 billion in the Americas. All those exposed to stable risk in the Americas were in the lowest endemicity class (PfPR2?10 �� 5%). The vast majority (88%) of those living under stable risk in CSE Asia were also in this low endemicity class; a small remainder (11%) were in the intermediate endemicity class (PfPR2?10 > 5 to PfPR2?10 �� 40%) areas. High endemicity was widespread in the Africa+ region, where 0.35 billion people are at this level of risk. Most of the rest live at intermediate risk (0.20 billion), with a smaller number (0.11 billion) at low stable risk. ConclusionsHigh levels of P. falciparum malaria endemicity are common in Africa. Uniformly low endemic levels are found in the Americas. Low endemicity is also widespread in CSE Asia, but pockets of intermediate and very rarely high transmission remain. There are therefore significant opportunities for malaria control in Africa and for malaria elimination elsewhere. This 2007 global P. falciparum malaria endemicity map is the first of a series with which it will be possible to monitor and evaluate the progress of this intervention process.背景：为高效调配资源开展疟疾防控干预，需精准掌握当前疟疾风险的空间分布特征。距上一幅全球疟疾流行区地图发布，已整整过去40年。本文详述了2007年恶性疟原虫（Plasmodium falciparum）疟疾流行区全新世界地图的构建流程。 方法与结果：通过多类全面检索策略，共检索到8938项恶性疟原虫感染率（Plasmodium falciparum Parasite Rate, PfPR）调查数据。其中7953项通过严格的数据保真度检验，被纳入全球PfPR数据库，且将数据按2~10岁年龄组进行标准化处理，以用于流行区制图。研究采用基于模型的地统计方法，在已明确界定的恶性疟原虫传播稳定空间范围内，构建了疟疾流行度的连续表面模型。该分析在贝叶斯（Bayesian）统计框架下实施，可对预测结果的不确定性开展稳健评估。不确定性以三种流行等级的正确预测概率表征，此前该分级已被确立为疟疾防控的实用参考指南。随后结合2007年全球人口分布表面数据，并针对非洲城市化对疟疾传播的调控效应进行校正，估算了各区域的风险暴露人口。在13.8亿面临稳定恶性疟原虫感染风险的人群中，6.9亿分布于中亚及东南亚（Central and South East Asia, CSE Asia），6.6亿分布于非洲、也门及沙特阿拉伯（简称非洲+区域），0.4亿分布于美洲。美洲所有面临稳定感染风险的人群均处于最低流行等级（PfPR2~10 ≤5%）。中亚及东南亚区域绝大多数（88%）的稳定风险暴露人群也处于该低流行等级；剩余小部分（11%）处于中等流行等级（PfPR2~10 >5%且≤40%）。高流行等级在非洲+区域广泛分布，共有3.5亿人群处于该风险等级。其余大部分人群处于中等风险等级（2.0亿），仅少量人群（1.1亿）处于低稳定风险等级。 结论：恶性疟原虫疟疾的高流行等级在非洲极为普遍。美洲全域均为低流行等级。中亚及东南亚区域也广泛分布低流行区，但仍存在局部中等流行区，极少数区域存在高传播等级。因此，非洲地区仍存在大量疟疾防控机遇，而其他区域则具备疟疾消除的潜力。本2007年全球恶性疟原虫疟疾流行区地图是一系列用于监测、评估疟疾防控干预进展的研究成果中的首幅作品。