Department of Public Health Medicine, School of Nursing and Public Health, University of KwaZulu-Natal, Durban, South Africa.
Geography Department, Faculty of Science, Bindura University of Science Education, Bag 1020, Bindura, Zimbabwe.
Malar J. 2017 Nov 21;16(1):476. doi: 10.1186/s12936-017-2116-1.
Although there has been a decline in the number of malaria cases in Zimbabwe since 2010, the disease remains the biggest public health threat in the country. Gwanda district, located in Matabeleland South Province of Zimbabwe has progressed to the malaria pre-elimination phase. The aim of this study was to determine the spatial distribution of malaria incidence at ward level for improving the planning and implementation of malaria elimination in the district.
The Poisson purely spatial model was used to detect malaria clusters and their properties, including relative risk and significance levels at ward level. The geographically weighted Poisson regression (GWPR) model was used to explore the potential role and significance of environmental variables [rainfall, minimum and maximum temperature, altitude, Enhanced Vegetation Index (EVI), Normalized Difference Vegetation Index (NDVI), Normalized Difference Water Index (NDWI), rural/urban] and malaria control strategies [indoor residual spraying (IRS) and long-lasting insecticide-treated nets (LLINs)] on the spatial patterns of malaria incidence at ward level.
Two significant clusters (p < 0.05) of malaria cases were identified: (1) ward 24 south of Gwanda district and (2) ward 9 in the urban municipality, with relative risks of 5.583 and 4.316, respectively. The semiparametric-GWPR model with both local and global variables had higher performance based on AICc (70.882) compared to global regression (74.390) and GWPR which assumed that all variables varied locally (73.364). The semiparametric-GWPR captured the spatially non-stationary relationship between malaria cases and minimum temperature, NDVI, NDWI, and altitude at the ward level. The influence of LLINs, IRS and rural or urban did not vary and remained in the model as global terms. NDWI (positive coefficients) and NDVI (range from negative to positive coefficients) showed significant association with malaria cases in some of the wards. The IRS had a protection effect on malaria incidence as expected.
Malaria incidence is heterogeneous even in low-transmission zones including those in pre-elimination phase. The relationship between malaria cases and NDWI, NDVI, altitude, and minimum temperature may vary at local level. The results of this study can be used in planning and implementation of malaria control strategies at district and ward levels.
尽管自 2010 年以来津巴布韦的疟疾病例数量有所下降，但该疾病仍是该国最大的公共卫生威胁。津巴布韦南马塔贝莱兰省的贡达区已进入疟疾消除前阶段。本研究旨在确定以病房为单位的疟疾发病率的空间分布，以改善该地区的疟疾消除规划和实施。
采用泊松纯空间模型检测疟疾聚集及其属性，包括以病房为单位的相对风险和显著性水平。采用地理加权泊松回归（GWPR）模型探索环境变量[降雨量、最低和最高温度、海拔、增强植被指数（EVI）、归一化差异植被指数（NDVI）、归一化差异水体指数（NDWI）、农村/城市]和疟疾控制策略[室内滞留喷洒（IRS）和长效驱虫蚊帐（LLINs）]对以病房为单位的疟疾发病率空间模式的潜在作用和显著性。
确定了两个有意义的疟疾病例聚集区（p<0.05）：（1）贡达区南部的 24 病房，（2）城市自治市的 9 病房，相对风险分别为 5.583 和 4.316。半参数-GWPR 模型同时包含局部和全局变量，根据 AICc（70.882）优于全局回归（74.390）和假设所有变量都局部变化的 GWPR（73.364）。半参数-GWPR 在病房水平上捕捉到了疟疾病例与最低温度、NDVI、NDWI 和海拔之间的空间非平稳关系。LLINs、IRS 和农村/城市的影响没有变化，并作为全局术语保留在模型中。NDWI（正系数）和 NDVI（从负到正系数范围）在一些病房中与疟疾病例呈显著关联。IRS 对疟疾发病率有预期的保护作用。
即使在包括消除前阶段在内的低传播地区，疟疾发病率也存在异质性。疟疾病例与 NDWI、NDVI、海拔和最低温度之间的关系可能在局部水平上有所不同。本研究的结果可用于区县级和病房级疟疾控制策略的规划和实施。
