Background Heat waves have devastating health effects on human populations. Our previous study shows that heat waves had a higher risk for stroke mortality in Nanjing. Despite many studies of mortality risk for heat waves in urban areas, few studies have examined the spatial variations among different regions. Objectives We analyzed the stroke mortality of a heat wave in 2010 in Nanjing, China and investigated the spatial variability of stroke mortality risk between heat wave days and non-heat wave days. Methods Within each town of Nanjing, we calculated the stroke mortality during the heat wave (July 30-August 22, 2010) and a reference period (July 30-August 22, 2009). We estimated the rate ratios (RRs) of urban, suburban, and rural regions. Spatial autocorrelation was used to measure the spatial patterns of heat wave mortality. The Anselin Local Moran's I statistic was applied to identify the statistically significant spatial clusters. Results Stroke mortality in both the heat wave and the reference period were spatially clustered, with the Moran's Index of 0.147 and 0.089. During the reference period, two HH spots(areas with high stroke mortality surrounded by other areas with high stroke mortality) were found in rural regions and the clusters in urban and suburban regions were not significant. During the heat wave, the two hot spots in rural regions remained while an HL spot (areas with high mortality surrounded by other areas with low mortality) was discovered in the suburban region. During the heat wave, the RRs of stroke mortality were 2.25(95%CI,1.03-4.27) in the urban area, 4.14(95%CI,2.77-5.95) in the suburban area, and 1.66(95%CI,1.33-2.05) in the rural area. Conclusions We found that stroke mortality risk from heat waves in Nanjing has clear spatial patterns. During the heat wave, suburban regions have the highest and spatially clustered stroke mortality risk. These findings revealed the importance of the health impact of heat waves in suburban areas.
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