Risk factors for chronic obstructive pulmonary disease in never-smokers: A systematic review

Introduction Relatively little is known about the risk factors for chronic obstructive pulmonary disease (COPD) in never-smokers, and these factors have not yet been fully characterised. This study therefore sought to analyse COPD risk factors in never-smokers by conducting a systematic review of the literature on the topic. Materials and methods We performed a search in PubMed (Medline) and Embase from 2000 onwards, to locate studies on COPD in never-smokers. For literature search and evidence synthesis purposes, we used the PRISMA guidelines and drew up a specific quality scale to quantify the evidence of each study included. Results The bibliographic search retrieved a total of 557 papers, 20 of which fulfilled the designated inclusion criteria (two case-control studies, four cohort studies and 14 cross-sectional studies). These studies were undertaken in Europe, the United States, Latin America, Asia and Africa. The risk factors for never-smokers were varied and ranged from exposure to biomass, occupational exposure and passive smoking to having a history of asthma, tuberculosis or respiratory infections during childhood. The effect of residential radon was unclear. The highest risk was obtained for previous respiratory diseases of any type, with a magnitude much higher than that observed for other risk factors. Conclusions There are few studies on COPD risk factors in never-smokers. More purpose-designed studies in this subpopulation are thus called for, including well-designed studies to specifically assess if indoor radon has any role on COPD onset.