Asthma hospitalisations and heat exposure in England: a case-crossover study during 2002-2019

BackgroundPrevious studies have found an association between warm temperature and asthma hospitalisation. They have reported different sex- and age-related vulnerabilities, nevertheless little is known about how this effect has changed over time and how it varies in space. This study aims to evaluate the association between asthma hospitalisation and warm temperature and investigate vulnerabilities by age, sex, time, and space.MethodsWe retrieved individual-level data on summer asthma hospitalisation at high temporal (daily) and spatial (postcodes) resolution during 2002-2019 in England from the NHS Digital. Daily mean temperature at 1km x 1km resolution was retrieved from the UK Met Office. We focused on lags 0-3 days. We employed a case-cross over study design and fitted Bayesian hierarchal Poisson models accounting for possible confounders (rainfall, relative humidity, wind speed, national holidays, and recurrent hospitalisations).ResultsAfter accounting for confounding, we found a 0.85% (95% Credible Interval: 0.64% to 1.07%) increase in the asthma hospitalisation risk for every 1°C increase in the ambient summer temperature. The effect was highest for males aged 15-65 (2.44%, 1.99% to 2.90%). During 2002-2007 we observed a 2.23% (1.86% to 2.60%) increase in hospitalisation risk per 1°C increase in temperature, whereas inconclusive evidence for the periods 2008-2013 and 2014-2019. Populations in Yorkshire and the Humber and East Midlands were the most vulnerable.ConclusionThis study provides evidence of an association between warm temperature and hospital admission for asthma, which was attenuated over time suggesting adaptive mechanisms to heat exposure or differences in lifestyle, comorbid conditions, and occupation over time.