Air pollution and chronic bronchitis: the evidence firms up

Chronic bronchitis is defined epidemiologically as cough and sputum production for ≥3 months in each of at least two consecutive years.1 It affects about a third of patients with chronic obstructive pulmonary disease but also occurs in individuals with normal lung function, with prevalence estimates varying widely.2–7 While it is not, by itself, associated with a substantially higher risk of death,8 it is associated with exacerbations of disease, incapacity and poor quality of life. The identification of chronic bronchitis was standardised in the first instance by the British Medical Research Council questionnaire,9 and subsequently, the questions were introduced into other respiratory symptom questionnaires. Ambient air pollution is increasingly being linked to a range of human conditions, and in the case of chronic bronchitis, which affects over two million individuals in the UK,10 there is some evidence of an association between the incidence or prevalence of chronic bronchitis and long-term exposure to air pollution.11–13 Early reports, however, relate to a time when the bulk of outdoor air pollution came from coal burning …