The impact of acute air pollution fluctuations on bronchiectasis pulmonary exacerbation: a case-crossover analysis

In bronchiectasis, exacerbations are believed to be triggered by infectious agents, but often no pathogen can be identified. We hypothesised that acute air pollution exposure may be associated with bronchiectasis exacerbations. We combined a case-crossover design with distributed lag models in an observational record linkage study. Patients were recruited from a specialist bronchiectasis clinic at Ninewells Hospital, Dundee, UK. We recruited 432 patients with clinically confirmed bronchiectasis, as diagnosed by high-resolution computed tomography. After excluding days with missing air pollution data, the final model for particles with a 50% cut-off aerodynamic diameter of 10 mu m (PM10) was based on 6741 exacerbations from 430 patients and for nitrogen dioxide (NO2) it included 6248 exacerbations from 426 patients. For each 10 mu g.m(-3) increase in PM10 and NO2, the risk of having an exacerbation that same day increased significantly by 4.5% (95% CI 0.9-8.3) and 3.2% (95% CI 0.7-5.8) respectively. The overall (lag zero to four) increase in risk of exacerbation for a 10 mu g.m(-3) increase in air pollutant concentration was 11.2% (95% CI 6.0-16.8) for PM10 and 4.7% (95% CI 0.1-9.5) for NO2. Subanalysis showed higher relative risks during spring (PM10 1.198 (95% CI 1.102-1.303), NO2 1.146 (95% CI 1.035-1.268)) and summer (PM10 2.142 (95% CI 1.785-2.570), NO2 1.352 (95% CI 1.140-1.602)) when outdoor air pollution exposure would be expected to be highest. In conclusion, acute air pollution fluctuations are associated with increased exacerbation risk in bronchiectasis.