Association between short-term NO exposure and asthma exacerbations in East London: A time series regression model

Background There is strong interest in the relationship between short-term air pollution exposure and human health. Most studies in this field focus on serious health effects such as death or hospital admission, but air pollution exposure affects many people with less severe impacts such as exacerbations of respiratory conditions. Method We developed a time series regression model to quantify the relationship between daily NOx concentration and asthma exacerbations requiring oral steroids from primary care settings. Explanatory variables include daily NOx concentration measurements extracted from 8 available background and roadside monitoring stations in east London, and daily ambient temperature extracted for London City Airport, located in east London. Lags of NOx concentrations up to 21 days (3 weeks) were used in the model. Result Results of the time series modelling showed a significant relationship between NOx concentrations on each day and the number of oral steroid courses prescribed in the following three weeks. Atmospheric concentrations of NOx measured at roadside stations are a more effective indicator of future prescriptions of oral steroid courses than are measurements at background stations. This relationship has two main components, one during the first week and the other towards the end of the second week. We find that an increase of 1 μgm−3 in atmospheric concentration of NOx (mean 95.75 μgm−3) leads to an increase of about 2.7% in the mean of 30.9 prescriptions of oral steroid courses per day in the study area. There is a negative correlation between ambient temperature and asthma exacerbation, with a reduction of 1C∘ leading to an increase of about 1.4% in the mean number of prescriptions per day. We did not find any effects of daily precipitation or relative humidity additional to annual seasonal ones.