title: Excess winter mortality and cold temperatures in a subtropical city, Guangzhou, China.
abstract: BACKGROUND
  A significant increase in mortality was observed during cold winters in many temperate regions. However, there is a lack of evidence from tropical and subtropical regions, and the influence of ambient temperatures on seasonal variation of mortality was not well documented.
  
  
  METHODS
  This study included 213,737 registered deaths from January 2003 to December 2011 in Guangzhou, a subtropical city in Southern China. Excess winter mortality was calculated by the excess percentage of monthly mortality in winters over that of non-winter months. A generalized linear model with a quasi-Poisson distribution was applied to analyze the association between monthly mean temperature and mortality, after controlling for other meteorological measures and air pollution.
  
  
  RESULTS
  The mortality rate in the winter was 26% higher than the average rate in other seasons. On average, there were 1,848 excess winter deaths annually, with around half (52%) from cardiovascular diseases and a quarter (24%) from respiratory diseases. Excess winter mortality was higher in the elderly, females and those with low education level than the young, males and those with high education level, respectively. A much larger winter increase was observed in out-of-hospital mortality compared to in-hospital mortality (45% vs. 17%). We found a significant negative correlation of annual excess winter mortality with average winter temperature (rs=-0.738, P=0.037), but not with air pollution levels. A 1 °C decrease in monthly mean temperature was associated with an increase of 1.38% (95% CI:0.34%-2.40%) and 0.88% (95% CI:0.11%-1.64%) in monthly mortality at lags of 0-1 month, respectively.
  
  
  CONCLUSIONS
  Similar to temperate regions, a subtropical city Guangzhou showed a clear seasonal pattern in mortality, with a sharper spike in winter. Our results highlight the role of cold temperature on the winter mortality even in warm climate. Precautionary measures should be strengthened to mitigate cold-related mortality for people living in warm climate.
authors.affiliation: Department of Biostatistics, School of Public Health and Tropical Medicine, Southern Medical University, Guangzhou, Guangdong, China.
authors.forename: Chun-Quan
authors.initials: CQ
authors.lastname: Ou
authors.forename: Yun-Feng
authors.initials: YF
authors.lastname: Song
authors.forename: Jun
authors.initials: J
authors.lastname: Yang
authors.forename: Patsy Yuen-Kwan
authors.initials: PY
authors.lastname: Chau
authors.forename: Lin
authors.initials: L
authors.lastname: Yang
authors.forename: Ping-Yan
authors.initials: PY
authors.lastname: Chen
authors.forename: Chit-Ming
authors.initials: CM
authors.lastname: Wong
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000397:Air Pollution / Q000009:adverse effects; D002423:Cause of Death; D002648:Child; D002675:Child, Preschool; D002681:China; D002980:Climate; D003080:Cold Temperature / Q000009:adverse effects*; D005260:Female; D017052:Hospital Mortality; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D008875:Middle Aged; D015233:Models, Statistical; D012621:Seasons; D055815:Young Adult