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Progression from asthma to chronic obstructive pulmonary disease. Is air pollution a risk factor?


Rationale — Individuals with asthma chronic obstructive pulmonary disease (COPD) overlap syndrome (ACOS), have more rapid decline in lung function, more frequent exacerbations and poorer quality of life than those with asthma or COPD alone. Air pollution exposure is a known risk factor for asthma and COPD; however, its role in ACOS is not as well understood.

Objectives — To determine if individuals with asthma exposed to higher levels of air pollution have an increased risk of ACOS.

Methods — Individuals who resided in Ontario, Canada aged ≥18 years in 1996 with incident asthma between 1996 and 2009 and participated in the Canadian Community Health Survey (CCHS) were identified and followed until 2014 to determine the development of ACOS. Data on exposures to fine particulate matter (PM2.5) and ozone (O3) were obtained from fixed monitoring sites. Associations between air pollutants and ACOS were evaluated using Cox regression models.

Measurements and Main Results — Of the 6,040 adults with incident asthma who completed the CCHS, 630 were identified as ACOS cases. Compared to non-ACOS, the ACOS population had later onset of asthma, higher proportion of mortality, and more frequent ED visits prior to COPD diagnosis. The adjusted hazard ratios (HR) of ACOS and cumulative exposures to PM2.5 (per 10 µg/m3) and O3 (per 10 ppb) were 2.78 (CI: 1.62-4.78) and 1.31 (CI: 0.71-2.39) respectively.

Conclusions — Individuals exposed to higher levels of air pollution had nearly 3-fold greater odds of developing ACOS. Minimizing exposure to high levels of air pollution may decrease the risk of ACOS.



To T, Zhu J, Larsen K, Simatovic J, Feldman L, Ryckman K, Gershon A, Lougheed MD, Licskai C, Chen H, Villeneuve PJ, Crighton E, Su Y, Sadatsafavi M, Williams D, Carlsten C; Canadian Respiratory Research Network. Am J Respir Crit Care Med. 2016; 194(4):429-38. Epub 2016 Mar 7.

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