Elsevier

Environmental Research

Volume 169, February 2019, Pages 196-205
Environmental Research

Impact of heatwaves on daily outpatient visits of respiratory disease: A time-stratified case-crossover study

https://doi.org/10.1016/j.envres.2018.10.034Get rights and content

Highlights

  • Heatwaves significantly increased outpatient visits for respiratory disease in Cangnan, China.

  • Effects of heatwaves on outpatient visits varied across different subgroups for respiratory disease.

  • Vulnerable groups of respiratory disease during heatwaves were identified.

  • Confounders were controlled in the model.

Abstract

Objectives

This study aims to estimate the impact of heatwaves from July 2010 to October 2012 on daily outpatient visits for respiratory disease (RD) in Cangnan, China and identify vulnerable populations.

Methods

The definition of heatwave was a period at least 3 consecutive days with maximum temperature exceeding 35 °C in this study. A time-stratified case-crossover design was conducted to examine the relationship between heatwaves and outpatient visits for RD. Patient data for the period from 2010 to 2012 were collected from the Third People's Hospital of Cangnan and daily meteorological data for the same period were collected from the China Meteorological Data Service Center. Data regarding the air pollution index (API), a composite indicator of air pollution, were collected from the Data Center of the Chinese Ministry of Environmental Protection. RD were identified based on the 10th revision International Classification of Diseases (ICD-10) codes (J00-J99). A conditional Poisson regression model was applied to examine the heatwave-RD association using the Relative Risk (RR) while adjusting for meteorological and air pollution factors including temperature, rainfall, wind speed, pressure, humidity, sunshine hours and API.

Results

During the study period, 4 heatwaves occurred and a total of 1732 outpatient visits for RD were reported. Heatwaves increased the frequency of RD outpatient visits and the highest RR of total RD was 1.155% and 95% Confidence Intervals (95% CI) was 1.084–1.232 at Lag 0. For subcategories, heatwaves increased the risk of infectious RD (Lag 0: RR =1.182, 95% CI: 1.106–1.263) and decreased the risk of non-infectious RD ((Lag 6: RR =0.750, 95% CI: 0.568–0.990). Moreover, heatwaves showed adverse effects on acute upper respiratory infection (Lag 0: RR =1.306, 95% CI: 1.177–1.450). The RR of outpatient visits for RD was statistically significant in females (Lag 0: RR =1.161, 95% CI: 1.046–1.298), males (Lag 4: RR =1.161, 95% CI: 1.096–1.261), young people aged 4–17 years (Lag 0: RR =1.741, 95% CI: 1.524–1.990) and elders aged 65 years or older (Lag 5: RR =1.412, 95% CI: 1.111–1.794) during heatwaves.

Conclusions

Heatwaves had a significant harmful impact on daily outpatient visits for RD in Cangnan, especially for vulnerable population identified. These results can be used not only to strengthen the health education and protection of these vulnerable populations, but also to assist relevant organizations with developing intervention programmes and improving disease prevention and community care.

Introduction

Heatwaves are disastrous weather events characterized by a period of high temperatures. According to the Fifth Assessment Report on Climate Change by the Intergovernmental Panel on Climate Change (IPCC), warming of the climate system is unequivocal (IPCC, 2013). The newly published World Meteorological Organization (WMO) Statement on the State of the Global Climate also reported that the average global temperature for 2013–2017 was the highest five-year average on record (World Meteorological Organization, 2018). As climate warming continues to intensify, the increase of extreme weather events represented by heatwaves has become one of the most serious consequences of climate change (IPCC, 2007, IPCC, 2012). In many regions like northern and central America, Europe, southern Australia, and southern and eastern Asia, the length or number of heatwaves has increased since the middle of the 20th century and will very likely continue to increase with on-going climate change (IPCC, 2012, IPCC, 2014). The frequency, duration and intensity of heatwaves also showed a general increasing trend during the period from 1961 to 2010 in China, especially the southeast area (Ye et al., 2014). A recent Lancet Review reported that humankind suffered more than the global average temperature rise: exposure-weighted warming from 2000 to 2016 (0.9 °C) was much higher than the area­weighted warming (0.4 °C) during the same period (Watts et al., 2018).

As the frequency and severity of heatwaves are projected to increase in the world, more attention has been paid to study heatwave-disease associations for improving early warning systems and adaptation to heatwaves. The adverse effects of heatwaves on mortality have been well studied. Evidence from many regions of the world reveals a steady increase in deaths from cardiovascular disease, respiratory disease (RD), cerebrovascular disease and diabetes during heatwaves (Lubczyńska et al., 2015, Basagaña et al., 2011, Ma et al., 2015, Wang et al., 2012, Wang et al., 2015, Han et al., 2017, Arbuthnott and Hajat, 2017). Elderly people, women, children, and those with low education and limited social contact are particularly sensitive to heatwaves (Tong et al., 2014, Sun et al., 2014, Son et al., 2012, Xu et al., 2014, Herbst et al., 2014). But studies on associations between heatwaves and morbidity were much fewer and had inconsistent results. More studies need to be conducted in this field to gain reliable conclusions.

As one of the most common and significant diseases in the world, RD threatens human health severely with a high prevalence and heavy disease burden (Chang and Rivera, 2013). Among non-communicable diseases, RD is the third leading cause of death just after cardiovascular disease and cancer (GBD, Risk Factors Collaborators, 2015, 2016). Global warming is a major threat to respiratory health (De et al., 2013), and extreme temperature events like heatwaves are one of the main ways in which climatic change can promote or aggravate RD (Ayres et al., 2009). A considerable number of studies have investigated the impact of heatwaves on mortality and emergency hospital admissions for RD using data collected from developed areas such as Australia (Wang et al., 2012, Tong et al., 2014, Herbst et al., 2014, Vaneckova and Bambrick, 2013, Wilson et al., 2013), Europe (Lubczyńska et al., 2015, Basagaña et al., 2011, Arbuthnott and Hajat, 2017, van Loenhout et al., 2018, Tsangari et al., 2016, Smith et al., 2016) and the United States (Sherbakov et al., 2018, Reid et al., 2012, Fuhrmann et al., 2016, Ogbomo et al., 2016, Gronlund et al., 2016). For example, a review of studies conducted in the UK demonstrated an increase in heat-related mortality during heatwaves, with deaths from RD being more sensitive than those due to cardiovascular disease (Arbuthnott and Hajat, 2017). In Sydney, Australia, hospitalizations increased for RD during hot days from 1991 to 2009 (Vaneckova and Bambrick, 2013). Heatwaves occurring in California from 1999 to 2009 were also found to be associated with an increase in risk for RD (Sherbakov et al., 2018).

Up to now, very few studies have estimated the impact of heatwaves on morbidity in developing countries (Phung et al., 2016, Wang et al., 2012, Song et al., 2017). Compared with hospital admission/hospitalization and emergency department visit/services, outpatient visits have rarely been used as an indicator of morbidity. To our knowledge, there are no studies that have focused on the impact of heatwaves on outpatient visits for RD in less developed areas of China. Moreover, a Sydney study reported that the increase in morbidity was not shared homogeneously across subcategories of RD (Vaneckova and Bambrick, 2013). More research is needed to comprehensively analyze the impact of heatwaves on specific categories of RD in order to identify the subcategories most affected by heatwaves.

Therefore, a time-stratified case-crossover design combined with a conditional Poisson regression model was employed to evaluate the association between heatwaves and respiratory outpatient visits, including major and specific categories, using data collected in Cangnan from 2010 to 2012. Results can be used to better understand the impacts of heatwaves on respiratory morbidity, identify potential vulnerable populations in less developed areas and assist relevant organizations with improving disease prevention and community care.

Section snippets

Study area and study period

Cangnan is a coastal area located in the southern part of Wenzhou, Zhejiang Province. And Zhejiang is one of provinces suffered heatwaves with the highest frequency and intensity typically observed in China (Ye et al., 2014). Fig. 1 shows the location of the study region. It has a total area of 1, 261.08 square kilometers and the geographical coordinates of the regional center are 27°30′ north latitude and 120°23′ east longitude. Cangnan features a subtropical monsoon climate. The weather is

Heatwaves

During the study period, there were 4 heatwaves in Cangnan under the selected definition with a total of 17 days (heatwave periods). All heatwaves occurred in July and August. As for duration, the longest and shortest were 7 days and 3 days respectively. During the heatwave periods, the highest MaxT was 37.8 °C and average MeanT was 31.1°C. Details of each heatwave are shown in Table 1.

Outpatient visits for RD

A total of 25, 848 cases of RD were reported during the study period. Table 2 displays the characteristics of

Discussions

This study has quantified the association between heatwaves and outpatient visits for RD during the summer months from 2010 to 2012 in Cangnan in southeastern China. To our knowledge, the present study is the first to examine the relationship between heatwaves and outpatient visits for RD in a less developed area of China. Evaluating the impact of heatwaves on RD in this study will help us to better understand the effects of these weather events on underdeveloped districts and provide

Conclusions

The results of this study show that heatwaves significantly increase the risk of RD in Cangnan during the period from 2010 to 2012, which is consistent with relative effects in developed areas. Outpatient visits of respiratory infectious diseases, especially acute upper respiratory infections, were clearly easier to have a peak during heatwaves. Young people aged 4–17 and elderly people aged 65 years or older should be pay more attention in activities to reduce adverse effect during heatwaves.

Acknowledgments

We want to thank the Third People's Hospital of Cangnan, the National Meteorological Information Center and the Ministry of Environmental Protection for providing research data. The interpretation and the conclusions contained herein do not represent the views of these agencies. We also thank the assistance of James Barclay in English writing.

Funding

This work was supported by the National Basic Research Program of China (973 Program), China (Grant no. 2012CB955500-955502).

Conflict of interest

All authors have read and approved the final version of the manuscript with no competing interests.

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