[Acute impact of cold spells on mortality during 2001-2011 in Jiang'an district of Wuhan, China].

ABSTRACT

OBJECTIVE: To evaluate the association between cold spells and nonaccidental mortality from 2001 to 2011 in the Jiang'an District of Wuhan, China. METHODS: We collected mortality data for December 2001 to 2010 and January to March 2002 to 2011 in the study area. According to the International Classification of Diseases, we stratified the mortality data into three cause-specific categories nonaccidental mortality, cardiovascular mortality, and respiratory mortality. We also obtained meteorological data (from the China Meteorological Administration) and ambient pollution data (from the Wuhan Environmental Monitoring Center) during the same periods. In the present study, a cold spell was defined as 5 or more consecutive days with daily average temperatures below the 5th percentile of daily mean temperatures (2.58 ℃) from January to December in 2001-2011. A distributed lag nonlinear model (DLNM) was applied to assess the acute effect of cold spells on daily nonaccidental mortality. RESULTS: During the study period, the total number of nonaccidental deaths was 17 119, including 9 403 (75.5%) among individuals aged over 65 years; 7 968 (46.5%) people died of cardiovascular disease. According to this definition, there were a total of 13 cold spell events and 111 days of duration in Wuhan during the study period. Study days were divided into three periods non-cold spell days, 2008 cold spell days, and cold spell days in other years. Average daily mean temperatures of the above three periods were (8.2±4.5), (-0.7±1.4), and (0.8±1.2) ℃, respectively, corresponding to average daily deaths of 14.0±4.2, 18.2±4.5, and 14.9±4.9 for nonaccidental mortality. After adjusting for long-term trends, seasonal trends, weekdays, holidays, and relative humidity, analysis by the DLNM revealed that cold spells were associated with increased mortality risk, with a cumulative relative risk (RR) of 1.56 (95% CI 1.36-1.79) at lag 0-27 days in 2008, higher than that in other years with 1.23 (95%CI 1.08-1.41). Cold spells were not significantly associated with respiratory mortality and people under 65 years of age; however, during the 2008 cold spell RR increased to 1.96 (95% CI 1.62-2.37) and 1.67 (95% CI 1.43-1.95) for cardiovascular mortality and older adults (≥65 years old), respectively; both males and females had high mortality risk, with RRs of 1.60 (95%CI1.33-1.92) and 1.50 (95% CI 1.23-1.84), respectively. The association between cold spells and mortality remained nearly unchanged with and without adjustment for ambient pollutants (PM10, SO2, and NO2) in the DLNMs. CONCLUSION: In Wuhan, both the 2008 cold spell and cold spells in other years were significantly associated with increased nonaccidental mortality. People with cardiovascular disease and elderly adults may be more susceptible to the impact of cold spells on mortality.