Impacts Of Meteorological Factors On Residential Mortality In Guangzhou, China

BackgroundThe impacts of meteorological factors on health outcomes have become growing concerns to governments; researchers and public, as climate change is associated with an increase in the frequency, intensity and duration of extreme weather events (e.g., heat waves and floods).Extensive epidemiological studies have consistently shown that mortality is associated with ambient temperatures. However, most of previous researches came from developed countries in temperate regions. Less evidence on weather factors and mortality was conducted in developing countries. In fact, populations in these countries were anticipated to be more vulnerable to climate change, due to poor living condition and limited capacity of coping with heat and cold weather.It is required to understand the characteristics of health impacts of these adverse events for assessing the impact of climate change. Previous studies focused on ambient temperatures, measured by daily mean temperature, maximum and minimum temperature. Diurnal temperature range (DTR), defined as the difference between daily maximum temperature and minimum temperature, is viewed as an important meteorological indicator associated with global climate change. Relative humidity and atmospheric pressure are also important weather indicators. However, little literature is available on the impacts of DTR, relative humidity and atmospheric pressure on mortality.ObjectiveThis study was conducted in Guangzhou, a subtropical city in mainland China. I aimed to examine the association between mortality and a variety of meteorological measures, including mean temperature, diurnal temperature change (DTR), relative humidity, atmospheric pressure and heat waves. I also explored the potential interaction between temperature and above meteorological factors. And I identified the subpopulations that are more vulnerable to the effects of meteorological measures.MethodsData sourcesThe Guangzhou Bureau of Health provided individual information for112,280deaths at the six urban areas in Guangzhou from1January2003to31December2007, including date of birth, date of death, cause of death, sex, educational attainment and occupation. We collected individual data for all77,099registered deaths between1January2008and31December2010from Guangzhou Center for Disease Control and Prevention.Daily meteorological data were obtained from China Meteorological Data Sharing System, including daily mean temperature, minimum and maximum temperature, relative humidity and atmospheric pressure. Weather data were collected from a single station (Wushan station) in Guangzhou. Daily data on particulate matter less than10μm in aerodynamic diameter (PM10), nitrogen dioxide (NO2) and sulphur dioxide (SO2) were obtained from Guangzhou Bureau of Environmental Protection.Statistical methodsA Poisson regression model combined with distributed lag non-linear model (DLNM) was applied to assess the non-linear and lag patterns of the association between daily mean temperature and mortality in Guangzhou. Effects of DTR, relative humidity and atmospheric pressure were examined by using a Poisson regression model combined with DLNM, after controlling for daily mean temperature, air pollutants, season and day of the week. The joint effects of DTR/relative humidity/atmospheric pressure and mean temperature were fitted by a natural spline. The impact of heat wave was assessed by calculating excess deaths and rate ratio (RR) of mortality comparing the case period to a summer reference period in the same year.ResultsHot effect was immediate and limited to the first5days, with an overall increase of15.46%(95%confidence interval:10.05%to20.87%) in mortality risk comparing the99th and the90th percentile temperature. Cold effect persisted for approximately12days, with a20.39%(11.78%to29.01%) increase in risk comparing the first and the10th percentile temperature. The effects were especially remarkable for cardio-respiratory mortality. The effects of both hot and cold temperatures were greater among the elderly. Females suffered more from hot-related mortality than males. The educational attainment and occupation class significantly modified coldand hot effects.The effect of DTR generally appeared immediately and lasted for4days for all cause-specific deaths. A1℃increase in DTR at lag0-4days was associated with a0.47%(95%confidence interval:0.01%-0.93%) increase in non-accidental mortality. Stroke mortality was most sensitive to DTR. Female, the elderly and those with low education were more susceptible to DTR than male, the youth and those with high education, respectively. Joint effects of DTR and daily mean temperature on mortality were observed when mean temperature was lower than22℃.A decrease in atmospheric pressure and relative humidity was associated with an increase in mortality, in particular cardiovascular mortality. Women, people aged≥75, and those with non-education were more sensitive to decreased atmospheric pressure and relative humidity than men, those aged<74, and those with higher education, respectively. Low atmospheric pressure and relative humidity increased the temperature effect on mortality. Extreme high atmospheric pressure also elevated the temperature-related mortality.During2003-2006, a9day heat wave was identified from July12to July21in2005. During this heat wave, the total number of excess deaths was145with an average of12deaths per day. We found statistically significant effect of the heat wave on non-accidental mortality (RR=1.23,95%CI:1.11-1.37). Greater effects were observed for cardiovascular mortality (RR=1.34,95%CI:1.13-1.59) and respiratory mortality (RR=1.31,95%CI:1.02-1.69). Females, the elderly and persons with lower socioeconomic status were at significantly higher risk of heat wave-related mortality.ConclusionsCold and hot temperatures, DTR, low relative humidity and atmospheric pressure were associated with increased risk of mortality in subtropical city of Guangzhou, China. Joint effects were observed between DTR and low mean temperature, and between low relative humidity/atmospheric pressure and mean temperature. The elderly, females, persons with low socioeconomic status and subjects with cardio-respiratory diseases have been identified as especially vulnerable to the effects of meteorological factors.Our findings highlight a need to strengthen risk perception and protective behaviors against adverse weather effects. Particularly, cold exposure is still an important mortality risk even in subtropical climate, providing strong evidence for the necessity of constructing a central heating system in Southern China. This knowledge can also help develop early warning system of extreme temperature and impending large temperature change in current day and build targeting strategies to protect those vulnerable subpopulations from adverse weather impacts.