Cigarette smoking: a risk factor for idiopathic pulmonary fibrosis.

We conducted a multicenter case-control study of clinically and histologically diagnosed idiopathic pulmonary fibrosis (IPF), a chronic diffuse interstitial lung disease of unknown cause. The study included 248 cases, and 491 control subjects identified through random-digit dialing, matched to cases in sex, age, and geographic region. Telephone interviews were conducted with both cases and controls to collect information on potential risk factors for IPF, including smoking and household, occupational, and environmental exposures. Pulmonary function tests, X-rays, computed tomographic (CT) scans of the chest, and lung biopsy reports were submitted by referring centers to support the diagnoses. An a priori hypothesis that smoking is associated with IPF was examined with conditional logistic regression analyses. More cases (72%) than control subjects (63%) had a history of ever smoking. The odds ratio (OR) for ever smoking was 1.6 (95% CI: 1.1 to 2.4). Risk was significantly elevated for former smokers (OR =...