Extreme temperatures and paediatric emergency department admissions

Transcription

1 JECH Online First, published on November 22, 2013 as /jech Research report Extreme temperatures and paediatric emergency department admissions Zhiwei Xu, 1 Wenbiao Hu, 2 Hong Su, 3 Lyle R Turner, 1 Xiaofang Ye, 1,4 Jiajia Wang, 1 Shilu Tong 1 1 School of Public Health and Social Work & Institute of Health and Biomedical Innovation, Queensland University of Technology, Kelvin Grove, Queensland, Australia 2 School of Population Health, University of Queensland, Brisbane, Queensland, Australia 3 Department of Epidemiology and Health Statistics, School of Public Health, Anhui Medical University, Hefei, Anhui, China 4 Shanghai Meteorological Bureau, Shanghai, China Correspondence to Dr Shilu Tong, School of Public Health and Social Work & Institute of Health and Biomedical Innovation, Queensland University of Technology, Kelvin Grove, QLD 4059, Australia; s.tong@qut.edu.au Received 9 April 2013 Revised 14 September 2013 Accepted 6 November 2013 To cite: Xu Z, Hu W, Su H, et al. J Epidemiol Community Health Published Online First: [ please include Day Month Year] doi: /jech ABSTRACT Background Children are particularly vulnerable to the effects of extreme temperatures. Objective To examine the relationship between extreme temperatures and paediatric emergency department admissions (EDAs) in Brisbane, Australia, during Methods A quasi-poisson generalised linear model combined with a distributed lag non-linear model was used to examine the relationships between extreme temperatures and age-, gender- and cause-specific paediatric EDAs, while controlling for air pollution, relative humidity, day of the week, influenza epidemics, public holiday, season and long-term trends. The model residuals were checked to identify whether there was an added effect due to heat waves or cold spells. Results There were EDAs among children during the study period. Both high (RR=1.27; 95% CI 1.12 to 1.44) and low (RR=1.81; 95% CI 1.66 to 1.97) temperatures were significantly associated with an increase in paediatric EDAs in Brisbane. Male children were more vulnerable to temperature effects. Children aged 0 4 years were more vulnerable to heat effects and children aged years were more sensitive to both hot and cold effects. High temperatures had a significant impact on several paediatric diseases, including intestinal infectious diseases, respiratory diseases, endocrine, nutritional and metabolic diseases, nervous system diseases and chronic lower respiratory diseases. Low temperatures were significantly associated with intestinal infectious diseases, respiratory diseases and endocrine, nutritional and metabolic diseases. An added effect of heat waves on childhood chronic lower respiratory diseases was seen, but no added effect of cold spells was found. Conclusions As climate change continues, children are at particular risk of a variety of diseases which might be triggered by extremely high temperatures. This study suggests that preventing the effects of extreme temperature on children with respiratory diseases might reduce the number of EDAs. INTRODUCTION Climate change has been recognised as the biggest global threat to health in the 21st century. 1 The average global surface temperature has increased, and the frequency and intensity of extreme weather events have also risen, 2 3 posing a huge threat to human health and well-being. In particular, the adverse effects of extreme temperatures on morbidity have become a great public health concern. 4 Previous studies of the impact of temperature on morbidity have focused mainly on adults, particularly the elderly. 5 6 Children are particularly vulnerable to environmental hazards, 7 11 but limited studies have examined the relationship between temperature and morbidity among children. 12 In previous studies, temperature was considered as a continuous risk factor, and the exposure response relationship between temperature and specific paediatric morbidity was assessed. However, to date, no study has quantified the effects of extreme temperatures on a wide range of health outcomes among children. Some public health publications have emphasised that persistent extreme temperatures may increase the incidence of paediatric diseases. Heat waves (or cold spells) were more likely to be considered as a distinct event in the literature, and the excess morbidity due to heat waves (or cold spells) was calculated by comparing heat wave (or cold spell) days with non-heat-wave (or non-cold-spell) days Some researchers have argued that the effects of heat waves and cold spells on human health might be due to the main effect of daily temperature fluctuations, and also the added effect of persistent extreme temperatures To the best of our knowledge, no study has separately quantified the effects of daily temperatures and added the effects of persistent extreme temperatures on paediatric morbidity. This study examined three key questions: (i) what is the relationship between extreme temperatures and paediatric emergency department admissions (EDAs) in Brisbane, Australia? (ii) is there any added effect due to heat waves and cold spells? (iii) which subgroups of children are more sensitive to extreme temperatures? METHODS Data collection Brisbane is the capital of Queensland, located on the east coast of Australia ( S, E). It has a subtropical climate, and generally experiences mild winters and hot summers, and thus the heat health relationship in Brisbane needs particular research attention Children aged 0 14 years account for 20% of the residential population in Brisbane. 23 EDA data for the period 1 January 2003 to 31 December 2009 were obtained from Queensland Health. Before the data were collected, ethical approval was obtained from the human research ethics committee of Queensland University of Technology. Because the data were de-identified and aggregated, written consent was not needed. Data on EDAs were classified according to the International Classification of Disease, 10th version. The main paediatric diseases in Brisbane during were analysed, including all-cause Copyright Article author (or their employer) Produced by BMJ Publishing Group Ltd under licence. Xu Z, et al. J Epidemiol Community Health 2013;0:1 8. doi: /jech

2 diseases, intestinal infectious diseases (A00 A09), endocrine, nutritional and metabolic diseases (E00 E90), nervous system diseases (G00 G99), respiratory diseases ( J00 J99), acute upper respiratory infections ( J00 J06), chronic lower respiratory diseases ( J40 J47) (most of which were EDAs for childhood asthma), digestive system diseases (K00 K93) and genitourinary system diseases (N00 N99). Daily data on maximum and minimum temperatures and relative humidity in Brisbane for the same period were retrieved from the Australian Bureau of Meteorology. Daily data on average particulate matter 10 mm (PM 10 ) (mg/m 3 ) and 8 h maximum ozone (O 3 ) (ppb) were obtained from the Queensland Department of Environmental and Resources Management. The data were collected from two monitor stations in Brisbane, and then averaged. Definitions of heat wave and cold spell To date, owing to variations in population characteristics and adaptation, there are no standard definitions for heat waves and cold spells. In this study, we combined intensity and duration of extreme temperatures to define both heat waves and cold spells: (1) intensity: the 4th (13.5 C) and 5th (13.8 C) centiles of daily mean temperature as the cold threshold, and the 95th (26.5 C) and 96th (26.7 C) centiles of the daily mean temperature as the hot threshold; (2) duration: a minimum of 2 4 consecutive days with temperatures below the cold threshold or above the hot threshold. Statistical analyses Stage I: estimation of the main temperature effects on paediatric EDAs To quantify the main effect of temperature on paediatric EDAs, we used a quasi-poisson generalised linear regression model combined with a distributed lag non-linear model (DLNM). Many studies have reported a lagged effect of temperature on morbidity Further, the temperature morbidity relationship has been found to be non-linear. 29 Thus, we used the DLNM to examine both non-linear and lagged effects of temperature simultaneously. 30 Previous studies have reported that there is no best temperature indicator, and daily mean temperature was used in this study. A natural cubic spline natural cubic spline DLNM was used to examine the temperature effect using four degrees of freedom (df) and 4 df for the temperature and lag dimensions, respectively. Previous research has shown that the cold effects on morbidity last for more than 7 days, while heat effects are relatively acute. 4 We found that there was a negligible effect of temperature on paediatric EDAs for lags above 21 days, and we therefore used a maximum lag of 21 days to examine the effect of temperature. Several different covariates were included in the model. PM 10,O 3 and relative humidity were controlled for as potential confounders using a natural cubic spline with 4 df. Maximum lags of 21 days were also used for PM 10,O 3 and relative humidity. Seasonal and long-term trends were controlled for using a natural cubic spline with 8 df per year of data. Influenza epidemics and public holidays were also controlled for in the model. For the choice of df for all non-linear functions, we used a Poisson model and checked the Akaike information criterion and residuals. After the best df was chosen, we changed the Poisson model to a quasi-poisson model. Day of week was controlled for as a categorical variable. When all the other parameters had been confirmed, we checked the temperature EDAs plot and chose the reference temperature by visual inspection. We evaluated the relative risk of paediatric EDAs associated with high temperature ( 26.5 C, 95th centile of mean temperature) relative to the reference temperature (24.0 C). Similarly, we evaluated the relative risk of paediatric EDAs associated with low temperature ( 13.8 C, 5th centile of mean temperature) relative to the reference temperature (24.0 C). Stage II: examining the added effects of heat waves and cold spells Previous studies have reported that sustained periods of heat and cold produce an added effect on mortality which is independent of main temperature effects We analysed the residuals of the stage I model to examine the possible added effects of heat waves and cold spells that is, we took the residuals of the model in stage I and then performed the analysis for heat waves and cold spells. We assumed a maximum lag of 21 days for the delayed effects of heat waves and cold spells. EDAs for childhood asthma on extreme temperature days were compared with non-extreme temperature days. Effect estimates were obtained for both male and female children, different age groups (0 4, 5 9 and years) and different EDA categories. To perform sensitivity analyses, we varied the df (8 15 per year) for time to control for both seasonal and long-term trend. We also varied the df (5 7) for temperature and humidity for the DLNM. All data analysis was conducted using the R statistical environment (V ) with the dlnm package used to fit the regression model. 34 Table 1 Summary statistics for mean temperature, relative humidity, air pollution, total and cause-specific paediatric EDAs in Brisbane, Australia, during Variables Mean SD Min Centile Max Mean temperature ( C) Relative humidity (%) O 3 (ppb) PM 10 (mg/m 3 ) Total morbidity Intestinal infectious diseases Endocrine, nutritional and metabolic diseases Nervous system diseases Respiratory diseases Acute upper respiratory infections Chronic lower respiratory diseases Digestive system diseases Genitourinary system diseases Total morbidity in children aged 0 4 years Total morbidity in children aged 5 9 years Total morbidity in children aged years Total morbidity in male children Total morbidity in female children EDA, emergency department admission; PM 10, particular matter 10 mm. 2 Xu Z, et al. J Epidemiol Community Health 2013;0:1 8. doi: /jech

3 Research report RESULTS In total, there were EDAs among children in the whole study period. Table 1 shows the summary statistics for mean temperature, relative humidity, air pollutants and total, cause-specific, age-specific and gender-specific paediatric EDAs. The average mean temperature was 20.6 C (range ), and the average relative humidity was 57.3% (5.0% 98.0%). The average values of O3 and PM10 were 22.3 ppb ( ) and 16.0 mg/m3 ( ), respectively. The daily number of EDAs was greater among children aged 0 4 years (mean 33.5, SD 11.2) than those aged 5 9 years (mean 9.3, SD 4.0) and years (mean 8.7, SD 3.9). The daily number of EDAs was greater among male children (mean 28.9, SD 9.6) than female children (mean 22.5, SD 7.9). Figure 1A presents the decomposed distribution of paediatric EDAs, showing a strong seasonal trend. The daily distributions of PM10, O3 and relative humidity are presented in figure 1B D. Figure 2 shows the cumulative effects of temperature on total, age- and gender-specific paediatric EDAs, and demonstrates that paediatric EDAs increased during both high and low temperatures. Hot and cold effects were much greater among male children than female children. For age-specific paediatric EDAs, it can be seen that children aged 0 4 years were vulnerable to heat effects, and those aged years were sensitive to both hot and cold effects. Figure 3 shows the effects of high temperature (95th centile (26.5 C) and low temperature (5th centile (13.8 C) relative to the threshold temperature (24.0 C)) on total paediatric EDAs according to the lags. Both hot and cold effects persisted, and cold effects were relatively more acute. Table 2 shows the cumulative effects of both high (26.5 C) and low (13.8 C) temperatures on total and cause-specific paediatric morbidity at lags of 0 1, 0 13 and 0 21 days. High Figure 1 (A) The daily distribution of paediatric emergency department admissions in Brisbane, from 2003 to (B) The daily distribution of particular matter 10 mm (PM10) in Brisbane, from 2003 to (C) The daily distribution of ozone (O3) in Brisbane, from 2003 to (D) The daily distribution of relative humidity in Brisbane, from 2003 to Xu Z, et al. J Epidemiol Community Health 2013;0:1 8. doi: /jech

4 Figure 2 The overall effect of temperature on paediatric emergency department admissions (EDAs). temperatures were statistically significantly associated with the following paediatric diseases: intestinal infectious diseases, respiratory diseases, endocrine, nutritional and metabolic diseases, nervous system diseases and chronic lower respiratory diseases. Low temperatures were significantly associated with intestinal infectious diseases, respiratory diseases and endocrine, nutritional and metabolic diseases. Table 3 shows the daily excess EDAs for total and causespecific paediatric EDAs on heat wave (or cold spell) days as opposed to non-heat wave (or non-cold spell) days. The number of heat waves and cold spells is shown in table 4. Using heat wave definitions of a minimum of 2 days temperature sustained over the 95th or 96th centile, we found there was no significant increase in total and cause-specific EDAs in heat waves. However, using heat wave definitions of a minimum of 3 days temperature sustained over the 95th or 96th centile, we found there were significant increases in EDAs for chronic lower respiratory diseases in heat waves. There was no significant increase in paediatric EDAs during cold spells. To conduct a sensitivity analysis, we changed the df (8 15 per year) for time to control for season. We also varied the df (5 7) for temperature and relative humidity, and found that the effects of high (26.5 C) and low (13.8 C) temperatures decreased slightly when the df for time, temperature or relative humidity was increased, but were still significant. DISCUSSION This study yielded several notable findings. Both high and low temperatures had significant impacts on paediatric EDAs. Male children were more vulnerable to temperature effects. Children aged 0 4 years were more vulnerable to heat effects and children aged years were more sensitive to both hot and cold Figure 3 The lagged effects of temperature on paediatric emergency department admissions (EDAs). 4 Xu Z, et al. J Epidemiol Community Health 2013;0:1 8. doi: /jech

5 Table 2 Cumulative effect of high and low temperatures on cause-specific paediatric EDAs, with 95th centile (26.5 C) and 5th centile (13.8 C) of temperature relative to reference temperature (24 C) Diseases Heat effect (RR (95% CI)) Cold effect (RR (95% CI)) Lag 0 1 Lag 0 13 Lag 0 21 Lag 0 1 Lag 0 13 Lag 0 21 Total paediatric morbidity 1.07 (1.04 to 1.10)* 1.34 (1.24 to 1.46)* 1.27 (1.12 to 1.44)* 1.11 (1.05 to 1.16)* 1.68 (1.57 to 1.78)* 1.81 (1.66 to 1.97)* Intestinal infectious diseases 1.06 (1.01 to 1.12)* 1.18 (0.98 to 1.43) 0.94 (0.70 to 1.27) 0.90 (0.80 to 1.01) 1.43 (1.23 to 1.66)* 1.74 (1.41 to 2.14)* Endocrine, nutritional and 1.01 (0.84 to 1.23) 1.34 (0.78 to 2.31) 1.80 (1.10 to 2.57)* 0.89 (0.65 to 1.22) 1.94 (1.28 to 2.93)* 2.05 (1.16 to 3.62)* metabolic diseases Nervous system diseases 1.06 (1.01 to 1.13)* 1.04 (0.64 to 1.69) 1.11 (0.52 to 2.38) 1.14 (0.85 to 1.53) 1.37 (0.94 to 2.00) 1.54 (0.92 to 2.59) Respiratory diseases 1.11 (1.05 to 1.16)* 1.67 (1.46 to 1.92)* 1.50 (1.21 to 1.86)* 1.31 (1.22 to 1.42)* 2.80 (2.52 to 3.12)* 2.67 (2.31 to 3.08)* Acute upper respiratory infections 1.08 (0.88 to 1.26) 1.12 (0.75 to 1.78) 1.15 (0.68 to 1.71) 1.23 (0.82 to 1.50) 1.10 (0.99 to 1.25) 1.83 (0.77 to 4.05) Chronic lower respiratory 0.98 (0.91 to 1.05) 1.13 (1.02 to 1.38)* 1.09 (1.01 to 1.46)* 0.96 (0.83 to 1.12) 1.05 (0.77 to 1.43) 0.80 (0.52 to 1.23) diseases Digestive system diseases 1.07 (0.98 to 1.17) 0.99 (0.84 to 1.18) 0.94 (0.74 to 1.21) 1.02 (0.84 to 1.23) 1.08 (0.73 to 1.60) 1.05 (0.61 to 1.79) Genitourinary system diseases 0.91 (0.82 to 1.02) 0.99 (0.77 to 1.29) 0.92 (0.63 to 1.35) 0.95 (0.75 to 1.20) 1.04 (0.64 to 1.68) 0.94 (0.48 to 1.84) *p<0.05. EDA, emergency department admission. effects. Both hot and cold effects persisted. Effects of high temperature were found on several paediatric diseases, including intestinal infectious diseases, respiratory diseases, endocrine, nutritional and metabolic diseases, nervous system diseases and chronic lower respiratory diseases. Low temperature significantly affected paediatric intestinal infectious diseases, respiratory diseases and endocrine, nutritional and metabolic diseases. No significant added effects due to heat waves or cold spells were seen, with the exception of an added effect of heat waves on paediatric chronic lower respiratory diseases. This study suggests that male children may be more vulnerable to extreme temperatures than female children, a finding that is supported by previous research The primary reasons for the observed gender difference in vulnerability to extreme temperatures may include variations in anthropometry, body composition (eg, sexual dimorphism) and social behaviour (eg, daily activity). During cold exposure, female children have a reduced thermal gradient for metabolic heat removal, and lower cardiovascular and metabolic responses than male children. 37 However, some researchers found that the risk of death increases in female children during heat waves and is greater than in male children. 38 Basu 39 argued that differences in the effect of temperature on male and female subjects varied among different locations and populations, indicating that the differences in vulnerability to extreme temperatures in the male children and female children of our study might also be due to socioeconomic characteristics and adaptive capacity of children in Brisbane. Another finding of our study is that children aged 0 4 or10 14 years are more vulnerable to extreme temperatures than children aged 5 9 years. Children 0 4 years of age have been found to be vulnerable to hot and cold, especially to persistent hot episodes Children aged years may play outdoors more often than younger children, which may increase their exposures to extreme temperatures. In young female children, menarche usually occurs between the age of 10 and 14, 17 and the increase in ovarian hormones among female children at this stage might influence their thermoregulation function, 44 resulting in their vulnerability to extreme temperatures. As the temperature changes, the automatic thermoregulation of humans responds to maintain thermal comfort so that mental and physical activities can be pursued without detriment to health. Temperatures exceeding these limits increase the risk of diseases. The lag structure of temperature effects on paediatric EDAs found in this study is not consistent with that found for the wider population. In this study, the effects of high temperature lasted for a couple of weeks, a figure that is not comparable with previous studies that reported shorter lag effects, indicating that high temperature may have a longer-lasting effect on children than on adults. We found that the cold effects on total paediatric EDAs lasted for 1 2 weeks, which is consistent with the lag duration of cold effects on other health outcomes, such as general practice consultations. 46 Although some of the findings are similar to those for other climates, the threshold temperatures for increases in morbidity and mortality vary with regions. In this study, we found associations for some commonly reported diseases in children, such as intestinal infectious diseases and respiratory diseases, and also for other conditions that have received less attention. These include endocrine, nutritional and metabolic diseases and nervous system diseases, indicating that parents and caregivers need to pay more attention to children during high and low temperatures. Admissions for respiratory disease were found to increase in both high and low temperatures in this study. The effect of low temperatures on respiratory diseases may be due partially to cross-infection from indoor crowding Low temperatures assist survival of bacteria in water droplets. 53 Furthermore, low temperatures may increase the incidence of paediatric influenza, and consequently, increase paediatric respiratory diseases. 54 Results from the adult population suggest that in cold temperatures respiratory tract infections may occur through either inhalation of cold air (eg, the temperature of the respiratory surface becomes optimal for virus transmission and replication), cooling of the body surface or through cold stress, which causes pathophysiological responses that may contribute to increased susceptibility to these infections. Cold stress might also alter the immune system and affect the susceptibility to respiratory tract infections The reasons for the effect of high temperatures on respiratory diseases are unknown. Interestingly, we found that childhood chronic lower respiratory disease was vulnerable to high temperatures, indicating that EDAs for this disease in Brisbane might increase in the future as climate change continues and the global surface average temperature increases. The results show that both high and low temperatures had large effects on endocrine diseases. These results correspond to Xu Z, et al. J Epidemiol Community Health 2013;0:1 8. doi: /jech

6 Table 3 Paediatric EDAs due to the added effect of heat waves and cold spells in Brisbane, Australia, from 2003 to 2009 Heat waves Cold spells th 96th 95th 96th 95th 96th 5th 4th 5th 4th 5th 4th Total paediatric morbidity 0( 3 to 3) 0( 5 to 4) 2( 7 to 11) 1 ( 11 to 9) 0( 2 to 1) 1( 2 to 3) 1( 4 to 5) 2( 3 to 8) 4( 6 to 15) 4( 6 to 15) Intestinal infectious diseases 1( 1 to 3) 0( 2 to 2) 1( 3 to 5) 2( 7 to 12) 1( 1 to 2) 2 (0 to 4) 2 ( 1 to 6) 3( 1 to 8) 6( 3 to 14) 6( 3 to 14) Endocrine to nutritional and metabolic diseases 0( 2 to 2) 1( 2 to 4) 1 ( 3 to 2) 2 ( 8 to 3) 0( 1 to 1) 0( 2 to 1) 1 ( 4 to 2) 2 ( 6 to 1) 5 ( 12 to 2) 5 ( 12 to 2) Nervous system diseases 1( 1 to2) 0( 2 to2) 2 ( 7 to3) 0( 7 to6) 0( 1 to2) 0( 1 to2) 0( 3 to3) 0( 3 to4) 0( 7 to7) 0( 7 to7) Respiratory diseases 0( 4 to 4) 1( 3 to 5) 7( 2 to 15) 4 ( 7 to 16) 1 ( 2 to 1) 1 ( 3 to 2) 2 ( 6 to 2) 0( 5 to 5) 0( 9 to 10) 0( 9 to 10) Acute upper respiratory infections 1 ( 2 to 4) 0( 2 to 2) 1( 7 to 9) 0( 8 to 9) 0( 2 to 2) 1( 1 to 2) 2( 1 to 5) 2( 1 to 6) 4( 1 to 10) 4( 1 to 10) Chronic obstructive pulmonary diseases 1 ( 1 to 3) 0( 2 to 2) 9 (1 to 15)* 11 (1 to 21)* 1( 1 to 2) 0( 1 to 1) 1 ( 3 to 1) 3( 2 to 9) 7( 2 to 16) 7( 2 to 16) Digestive system diseases 0( 2 to1) 1 ( 3 to1) 1( 5 to7) 3 ( 10 to 3) 1( 1 to2) 1( 1 to 3) 2 (0 to 5) 2 ( 2 to5) 4( 3 to10) 4( 3 to 10) Genitourinary system diseases 0( 2 to 1) 1 ( 3 to 1) 0( 4 to 4) 1( 3 to 5) 1 ( 2 to 0) 1 ( 3 to 1) 2 ( 4 to 1) 1 ( 5 to 2) 3 ( 10 to 4) 3 ( 10 to 4) *p<0.05 All the values in brackets refer to 95% CIs. EDA, emergency department admission. Table 4 The number of heat waves and cold spells in Brisbane, Australia, from 2003 to 2009 Heat waves Cold spells Number of consecutive days Centile* Days Centile* Days 2 95th 13 5th 19 96th 7 4th th 2 5th 4 96th 1 4th th 0 5th 1 96th 0 4th 1 *The threshold cut-off point which we used to define heat waves and cold spells. The number of heat wave and cold spell days. EDA, emergency department admission. those of a study conducted by Pudpong and Hajat 57 in Thailand, which demonstrated an increase of diabetic outpatient visits during high temperatures in the total population. Semenza et al 58 found that diabetic admissions increased during heat waves in Chicago. It was reported that the autonomic control and endothelial function of people with diabetes is sensitive to extreme temperatures, which may explain the biological mechanism. 59 We also found that low temperatures had an adverse effect on endocrine diseases, indicating that EDAs for childhood endocrine diseases may increase during cold days. We found that admissions for nervous system disease increased during hot days, possibly owing to the negative effects of some psychotropic drugs, decreased self-care capacity 60 and physiological vulnerability. 61 High temperatures may trigger the potential symptoms of people with existing nervous system disorders. We found that there were no added effects due to heat waves or cold spells except for paediatric chronic lower respiratory diseases. Thus the increase of paediatric EDAs during persistent extreme temperatures for Brisbane was mainly due to daily high or low temperatures, but not due to the effects caused by persistent periods of high or low temperatures. Persistent high temperatures were associated with 9 11 EDAs a day for paediatric chronic lower respiratory diseases, depending on the severity of heat waves. This indicates that parents and caregivers should take more protective measures during extreme temperatures and persistent hot days to prevent their children from chronic lower respiratory diseases attacks. Chronic lower respiratory disease was one of the leading causes of death globally in 2010, and the findings of this study show that the more intense, frequent and long heat waves in the future will probably increase the burden caused by this disease. Two reasons may explain the absence of an added effect during cold spells. First, children may wear more clothes after experiencing a cold day. Second, Brisbane has a subtropical climate and rarely has really cold days for more than a few days, reducing the likelihood of a cold spell occurring. Potential intervention strategies need to be developed for children s particular vulnerability to both low and high temperatures. The ideal way of handling extreme temperatures is through primary prevention for example, health education. 64 A heat early warning system can be of great use, especially for those parents whose children have a history of chronic lower respiratory diseases. Strengths and limitations This study has three major strengths. First, to the best of our knowledge, this is the first study which specifically examines the effect of extreme temperatures on a wide range of diseases in 6 Xu Z, et al. J Epidemiol Community Health 2013;0:1 8. doi: /jech

7 children in the Southern Hemisphere. Even though children are regarded as a population subgroup vulnerable to temperature extremes, little empirical research has been conducted to date. Second, advanced statistical methods were used to quantify the lagged and cumulative effects of extreme temperatures on paediatric EDAs. Finally, vulnerabilities to extreme temperatures among groups of different age and gender were assessed and compared. Three limitations of this study should also be acknowledged. First, we focused on only one city, which means that our findings should only be generalised to other regions and climates with caution. However, our findings may stimulate further research in other populations. Second, infants were not specifically analysed as a subgroup because of lack of data, even though they are particularly vulnerable to temperature effects. Further studies should focus more on the impact of extreme temperatures on morbidity in infants. Finally, there may be some exposure misclassification bias because we used aggregated data on temperature and air pollution rather than individual exposure data. CONCLUSIONS Our findings demonstrate significant effects of high and low temperatures on a variety of paediatric diseases. The added effects of persistent extreme temperatures on most paediatric EDAs appeared to be negligible when compared with the main effects, but paediatric chronic lower respiratory disease was very sensitive to both extreme temperatures and heat waves. In addition, male children, children aged 0 4 years, and children aged years were at particular risk. These findings indicate that parents and caregivers need to be aware of the adverse health effects of extreme temperatures and employ appropriate protective measures (eg, adjustment of exposure, clothing and hydration). What is already known on this subject Extreme temperatures have impacts on paediatric intestinal infectious diseases and respiratory diseases. Children aged 0 4 years are particularly vulnerable to extreme temperatures. What this study adds Our results show that male children are more vulnerable to temperature effects. Children aged 0 4 years are more vulnerable to heat effects and children aged years are more sensitive to both hot and cold effects. Hot temperature effects were seen on several paediatric diseases, including intestinal infectious diseases, respiratory diseases, endocrine, nutritional and metabolic diseases, nervous system diseases and chronic lower respiratory diseases, while low temperature significantly affected paediatric intestinal infectious diseases, respiratory diseases and endocrine, nutritional and metabolic diseases. There was an added effect of heat waves on paediatric chronic lower respiratory diseases. Acknowledgements We would like to thank Dr Cunrui Huang for his valuable comments on the early draft, and we greatly appreciate Dr Adrian Barnett s insightful comments on the manuscript revision. Contributors ZX and ST designed this study. ZX analysed the data and wrote the first draft. ST, WH, HS, LRT, XY and JW contributed to the manuscript revision. Funding ST was funded by a National Health and Medical Research Council research fellowship (No ). Competing interests None. Ethics approval Human research ethics committee of Queensland University of Technology. Provenance and peer review Not commissioned; externally peer reviewed. REFERENCES 1 Costello A, Abbas M, Allen A, et al. Managing the health effects of climate change. Lancet 2009;373: IPCC. Climate change 2007: synthesis report. Geneva, WHO. Protecting health from climate change World Health Day Geneva: World Health Organization, Ye X, Wolff R, Yu W, et al. Ambient temperature and morbidity: a review of epidemiological evidence. Environ Health Perspect 2011;120: Koken PJM, Piver WT, Ye F, et al. Temperature, air pollution, and hospitalization for cardiovascular diseases among elderly people in Denver. Environ Health Perspect 2003;111: Lan Chang C, Shipley M, Marmot M, et al. Lower ambient temperature was associated with an increased risk of hospitalization for stroke and acute myocardial infarction in young women. J Clin Epidemiol 2004;57: Hoffman JL. Heat-related illness in children. Clin Pediatr Emerg Med 2001;2: Committee on Environmental Health. Global climate change and children s health. Pediatrics 2007;120: Balbus JM, Malina C. Identifying vulnerable subpopulations for climate change health effects in the United States. J Occup Environ Med 2009;51: Sheffield P, Landrigan P. Global climate change and children s health: threats and strategies for prevention. Environ Health Perspect 2011;119: Dozor AJ, Amler RW. Children s environmental health. J Pediatr 2013;162:6 7.e2. 12 Xu Z, Etzel RA, Su H, et al. Impact of ambient temperature on children s health: a systematic review. Environ Res 2012;117: Guo Y, Jiang F, Peng L, et al. The association between cold spells and pediatric outpatient visits for asthma in Shanghai, China. PLoS ONE 2012;7:e Knowlton K, Rotkin-Ellman M, King G, et al. The 2006 California heat wave: impacts on hospitalizations and emergency department visits. Environ Health Perspect 2008;117: Kovats RS, Hajat S, Wilkinson P. Contrasting patterns of mortality and hospital admissions during hot weather and heat waves in Greater London, UK. Occup Environ Med 2004;61: Leonardi GS, Hajat S, Kovats RS, et al. Syndromic surveillance use to detect the early effects of heat-waves: an analysis of NHS Direct data in England. Soz Praventivmed 2006;51: Anderson CA, Zhu G, Falchi M, et al. A genome-wide linkage scan for age at menarche in three populations of European descent. J Clin Endocrinol Metab 2008;93: Gasparrini A, Armstrong B. The impact of heat waves on mortality. Epidemiology 2011;22: Hajat S, Armstrong B, Baccini M, et al. Impact of high temperatures on mortality: is there an added heat wave effect? Epidemiology 2006;17: Yu W, Vaneckova P, Mengersen K, et al. Is the association between temperature and mortality modified by age, gender and socio-economic status? Sci Total Environ 2010;408: Tong S, Wang XY, Guo Y. Assessing the short-term effects of heatwaves on mortality and morbidity in Brisbane, Australia: comparison of case-crossover and time series analyses. PLoS ONE 2012;7:e Wang XY, Barnett AG, Yu W, et al. The impact of heatwaves on mortality and emergency hospital admissions from non-external causes in Brisbane, Australia. Occup Environ Med 2012;69: Begg S, Vos T, Barker B, et al. The burden of disease and injury in Australia PHE 82. Canberra: Australian Institute of health and Welfare; aihw.gov.au/workarea/downloadasset.aspx?id= De Donato FK, Leone M, Noce D, et al. The impact of the February 2012 cold spell on health in Italy using surveillance data. PLoS ONE 2013;8:e Monteiro A, Carvalho V, Góis J, et al. Use of Cold Spell indices to quantify excess chronic obstructive pulmonary disease (COPD) morbidity during winter (November to March ): case study in Porto. Int J Biometeorol 2012;57: Tong S, Kan H. Heatwaves: what is in a definition? Maturitas 2011;69: Chang C, Shipley M, Marmot M, et al. Lower ambient temperature was associated with an increased risk of hospitalization for stroke and acute myocardial infarction in young women. J Clin Epidemiol 2004; Green R, Basu R, Malig B, et al. The effect of temperature on hospital admissions in nine California counties. Int J Public Health 2010;55: Xu Z, et al. J Epidemiol Community Health 2013;0:1 8. doi: /jech

8 29 Schwartz J, Samet JM, Patz JA. Hospital admissions for heart disease: the effects of temperature and humidity. Epidemiology 2004;15: Gasparrini A, Armstrong B, Kenward M. Distributed lag non-linear models. Statist Med 2010;29: Barnett AG, Tong S, Clements ACA. What measure of temperature is the best predictor of mortality? Environ Res 2010;110: Hajat S, Kosatky T. Heat-related mortality: a review and exploration of heterogeneity. J Epidemiol Community Health 2010;64: Anderson B, Bell M. Weather-related mortality: how heat, cold, and heat waves affect mortality in the United States. Epidemiology 2009;20: Gasparrini A, Armstrong B. Distributed lag non-linear models in R: the package dlnm Hutter HP, Moshammer H, Wallner P, et al. Heatwaves in Vienna: effects on mortality. Wien Klin Wochenschr 2007;119: Fouillet A, Rey G, Laurent F, et al. Excess mortality related to the August 2003 heat wave in France. Int Arch Occup Environ Health 2006;80: McArdle W, Toner M, Magel J, et al. Thermal responses of men and women during cold-water immersion: influence of exercise intensity. Eur J Appl Physiol 1992;65: Basagaña X, Sartini C, Barrera-Gómez J, et al. Heat waves and cause-specific mortality at all ages. Epidemiology 2011;22: Basu R. High ambient temperature and mortality: a review of epidemiologic studies from 2001 to Environ Health 2009;8: Nastos P, Paliatsos A, Papadopoulos M, et al. The effect of weather variability on pediatric asthma admissions in Athens, Greece. J Asthma 2008;45: Tourula M, Fukazawa T, Isola A, et al. Evaluation of the thermal insulation of clothing of infants sleeping outdoors in Northern winter. Eur J Appl Physiol 2011;111: Tourula M, Isola A, Hassi J, et al. Infants sleeping outdoors in a northern winter climate: skin temperature and duration of sleep. Acta Pædiatr 2010; 99: Nitschke M, Tucker G, Hansen A, et al. Impact of two recent extreme heat episodes on morbidity and mortality in Adelaide, South Australia: a case-series analysis. Environ Health 2011;10: Coyne MD, Kesick CM, Doherty TJ, et al. Circadian rhythm changes in core temperature over the menstrual cycle: method for noninvasive monitoring. Am J Physiol Regul Integr Comp Physiol 2000;279:R Lin S, Luo M, Walker RJ, et al. Extreme high temperatures and hospital admissions for respiratory and cardiovascular diseases. Epidemiology 2009;20: Hajat S, Haines A. Associations of cold temperatures with GP consultations for respiratory and cardiovascular disease amongst the elderly in London. Int J Epidemiol 2002;31: Checkley W, Epstein LD, Gilman RH, et al. Effects of EI Niño and ambient temperature on hospital admissions for diarrhoeal diseases in Peruvian children. Lancet 2000;355: Chou WC, Wu JL, Wang YC, et al. Modeling the impact of climate variability on diarrhea-associated diseases in Taiwan ( ). Sci Total Environ 2010;409: D Souza R, Hall G, Becker N. Climatic factors associated with hospitalizations for rotavirus diarrhoea in children under 5 years of age. Epidemiol Infect 2008;136: Hashizume M, Armstrong B, Hajat S, et al. Association between climate variability and hospital visits for non-cholera diarrhoea in Bangladesh: effects and vulnerable groups. Int J Epidemiol 2007;36: Ophir D, Elad Y. Effects of steam inhalation on nasal patency and nasal symptoms in patients with the common cold. Am J Otolaryngol 1987;8: Tyrrell D, Barrow I, Arthur J. Local hyperthermia benefits natural and experimental common colds. BMJ 1989;298: Handley BA, Webster AJF. Some factors affecting the airborne survival of bacteria outdoors. J Appl Microbiol 1995;79: Xu Z, Hu W, Williams G, et al. Air pollution, temperature and pediatric influenza in Brisbane, Australia. Environ Int 2013;59: Mäkinen TM, Juvonen R, Jokelainen J, et al. Cold temperature and low humidity are associated with increased occurrence of respiratory tract infections. Respir Med 2009;103: Mourtzoukou EG, Falagas ME. Exposure to cold and respiratory tract infections. Int J Tuberc Lung Dis 2007;11: Pudpong N, Hajat S. High temperature effects on out-patient visits and hospital admissions in Chiang Mai, Thailand. Sci Total Environ 2011;409: Semenza JC, McCullough JE, Flanders WD, et al. Excess hospital admissions during the July 1995 heat wave in Chicago. Am J Prev Med 1999;16: Schwartz J. Who is sensitive to extremes of temperature?: A case-only analysis. Epidemiology 2005;16: Bark N. Deaths of psychiatric patients during heat waves. Psychiatr Serv 1998;49: Hansen A, Bi P, Nitschke M, et al. The effect of heat waves on mental health in a temperate Australian city. Environ Health Perspect 2008;116: Lozano R, Naghavi M, Foreman K, et al. Global and regional mortality from 235 causes of death for 20 age groups in 1990 and 2010: a systematic analysis for the Global Burden of Disease Study Lancet 2012;380: Murray CJL, Vos T, Lozano R, et al. Disability-adjusted life years (DALYs) for 291 diseases and injuries in 21 regions, : a systematic analysis for the Global Burden of Disease Study Lancet 2012;380: Xu Z, Sheffield P, Su H, et al. The impact of heat waves on children s health: a systematic review. Int J Biometeorol 2013: Xu Z, et al. J Epidemiol Community Health 2013;0:1 8. doi: /jech