Greater temperature variation within a day associated with increased emergency hospital admissions for asthma

Highlights

• We examined the association between diurnal temperature range (DTR) and asthma.

• We observed greater DTR associated with increased emergency asthma hospitalizations.

• The effect of DTR was independent of daily mean/minimum temperature and air pollution.

• DTR exhibited significantly greater effect in cool season, in males and children.

• Great DTR was an environmental risk factor for asthma exacerbation.

Abstract

Asthma is one of the most common chronic conditions affecting both children and adults. Examining the health effects of environmental triggers such as temperature variation may have implications for maintenance of asthma control and prevention. We hypothesized that large diurnal temperature range (DTR) might be a source of additional environmental stress and therefore a risk factor for asthma exacerbation. Daily meteorological data, air pollution concentrations and emergency hospital admissions for asthma from 2004 to 2011 in Hong Kong were collected. Poisson regression models were used to fit the relationship between daily DTR and asthma, after adjusting for the time trend, seasonality, mean temperature, humidity, and levels of outdoor air pollution. Acute adverse effect of DTR on asthma was observed. An increment of 1 °C in DTR over lag0 to lag4 days was associated with a 2.49% (95% CI: 1.86%, 3.14%) increase in daily emergency asthma hospitalizations. The association between DTR and asthma was robust on the adjustment for daily absolute temperature and air pollution. DTR exhibited significantly greater effect in cool season. Males and female children appeared to be more vulnerable to DTR. Results supported that greater temperature variation within a day was an environmental risk factor for asthma exacerbation.

Introduction

Asthma is one of the most common chronic conditions affecting both children and adults. It is characterized by airway hyper-responsiveness to physiologic or environmental triggers. This hyper-responsiveness results in pronounced constriction of airway muscles, inflammation, swelling, mucus production, and subsequent respiratory distress (Subbarao et al., 2009). Risk factors for incident asthma among children included male sex, atopic sensitization, parental history of asthma, early-life stressors and infections, obesity, and exposure to indoor allergens, tobacco smoke and outdoor pollutants. Risk factors for adult-onset asthma included female sex, airway hyper-responsiveness, lifestyle factors, and work-related exposures (King et al., 2004). Although a family history of asthma is common, it is neither sufficient nor necessary for the development of asthma. The substantial increase in the incidence of asthma over the past few decades and the geographic variation in both base prevalence rates and the magnitude of the increases support that environmental factors play a large role in the current asthma epidemic (Subbarao et al., 2009).

Although the etiology of asthma has not been fully elucidated, there is evidence that the environmental risk factors such as prenatal cigarette smoking (Neuman et al., 2012), air pollution (Lee et al., 2006, Ko et al., 2007, Mar and Koenig, 2009), climate factors (Chen et al., 2006, D'Amato et al., 2010, Harju et al., 2010, Xu et al., 2013a), may increase the risk of asthma attacks. The diurnal temperature range (DTR), defined as the difference between maximal and minimal temperatures within one day, is a meteorological indicator which may be related to a variety of health outcomes (Chen et al., 2007, Liang et al., 2008, Cao et al., 2009, Tam et al., 2009, Lim et al., 2012). It is of interest whether the temperature variation within one day, i.e. DTR, is the risk factor for asthma independent of the corresponding absolute temperature. Only a few studies examined the associations between outdoor short-term temperature changes and asthma morbidity (Lim et al., 2012, Wasilevich et al., 2012, Xu et al., 2013b), and the results were conflicting with each other and inconclusive. The study conducted in four metropolitan areas in Korea (Lim et al., 2012) and the study conducted in Brisbane, Australia (Xu et al., 2013b) supported a positive association between DTR and asthma, while the other study conducted in Detroit, Michigan suggested a negligible association between short-term temperature change and emergency department visits for asthma among children (Wasilevich et al., 2012).

To examine the health effects of environmental triggers such as temperature variation may have implications for patient education and maintenance of asthma control and prevention. In this study, we hypothesized that large diurnal temperature change might be a source of additional environmental stress and therefore a risk factor for asthma exacerbation. We aimed to examine the associations between DTR and asthma, and to test the effect differences by season, age group and gender to identify the vulnerable subgroups.