Association of respiratory symptoms with use of high efficiency particulate air (HEPA) filters: a randomized controlled trial

Abstract

Background: Air pollution has been associated with increased respiratory symptoms, especially in patients with asthma and Chronic Obstructive Pulmonary Disease (COPD). While HEPA filters reduce air pollution in the home, whether they reduce respiratory symptoms is unknown. Methods: We conducted a 12-week randomized, blinded, cross-over, controlled trial of adult patients with a history of respiratory symptoms during air pollution. During 6 weeks of the trial, the HEPA filter insert was present (HEPA filter ON), and during the other 6 weeks it was not (HEPA filter OFF). We conducted symptom questionnaires at enrollment, cross-over, and at completion of the study. The primary outcome was change in St. George’s Respiratory Questionnaire - COPD (SGRQ-C) score. Secondary outcomes included change in COPD Assessment Test (CAT) score, and modified Medical Research Council (mMRC) score. Results: 52 patients were enrolled and (lower than expected) 35 had completed SGRQ-C scores during the study period. Overall, we found no significant difference in SGRQ-C, CAT, or mMRC scores. A sample size of 35 subjects provided 80% power to detect a difference of 5.5 units in the SGRQ-C measure of respiratory symptoms. The minimal clinically important difference of SGRQ-C is 4 units. Conclusion: In a small, randomized, blinded, cross-over, controlled trial use of HEPA filter was not associated with a change in respiratory symptoms during periods of air pollution. This negative study suggesting that the clinical effect of HEPA filter on symptoms in this type of exposure is limited.