Characterizing the relationship between temperature and mortality in tropical and subtropical cities: a distributed lag non-linear model analysis in Hue, Viet Nam, 2009–2013

Tran Ngoc Dang,Xerxes T Seposo,Nguyen Huu Chau Duc,Tran Binh Thang,Do Dang An,Lai Thi Minh Hang,Tran Thanh Long,Bui Thi Hong Loan,Yasushi Honda

doi:10.3402/gha.v9.28738

Abstract

BackgroundThe relationship between temperature and mortality has been found to be U-, V-, or J-shaped in developed temperate countries; however, in developing tropical/subtropical cities, it remains unclear.ObjectivesOur goal was to investigate the relationship between temperature and mortality in Hue, a subtropical city in Viet Nam.DesignWe collected daily mortality data from the Vietnamese A6 mortality reporting system for 6,214 deceased persons between 2009 and 2013. A distributed lag non-linear model was used to examine the temperature effects on all-cause and cause-specific mortality by assuming negative binomial distribution for count data. We developed an objective-oriented model selection with four steps following the Akaike information criterion (AIC) rule (i.e. a smaller AIC value indicates a better model).ResultsHigh temperature-related mortality was more strongly associated with short lags, whereas low temperature-related mortality was more strongly associated with long lags. The low temperatures increased risk in all-category mortality compared to high temperatures. We observed elevated temperature-mortality risk in vulnerable groups: elderly people (high temperature effect, relative risk [RR]=1.42, 95% confidence interval [CI]=1.11–1.83; low temperature effect, RR=2.0, 95% CI=1.13–3.52), females (low temperature effect, RR=2.19, 95% CI=1.14–4.21), people with respiratory disease (high temperature effect, RR=2.45, 95% CI=0.91–6.63), and those with cardiovascular disease (high temperature effect, RR=1.6, 95% CI=1.15–2.22; low temperature effect, RR=1.99, 95% CI=0.92–4.28).ConclusionsIn Hue, the temperature significantly increased the risk of mortality, especially in vulnerable groups (i.e. elderly, female, people with respiratory and cardiovascular diseases). These findings may provide a foundation for developing adequate policies to address the effects of temperature on health in Hue City.

Highlights

Climate change is a significant and emerging threat to public health in many countries worldwide, which directly relates to a short-term increase in mortality rates during exposure to low or high temperature [1]
High temperature-related mortality was more strongly associated with short lags, whereas low temperature-related mortality was more strongly associated with long lags
We observed elevated temperature-mortality risk in vulnerable groups: elderly people, females, people with respiratory disease, and those with cardiovascular disease

Summary

Introduction

Climate change is a significant and emerging threat to public health in many countries worldwide, which directly relates to a short-term increase in mortality rates during exposure to low or high temperature [1]. In a recent study by Guo et al [6] that assessed the global variation of high temperature and low temperature effects on mortality, a data set was collected and analyzed from 306 communities in 12 countries (Australia, Brazil, Thailand, China, Taiwan, Korea, Japan, Italy, Spain, the United Kingdom, the United States, and Canada); none of the 10 countries most affected by climate change mentioned above were included. This fact may cause an imbalance in assessing the impact of climate change on health.

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