Colder seasonal temperatures during winter and spring across regions within the United States and parts of Canada are associated with higher chronic obstructive pulmonary disease (COPD) exacerbation rates in older adults without cardiovascular disease, according to a study published in Annals of the American Thoracic Society.

In this retrospective study, a total of 1934 participants (1049 placebo participants from the previously conducted Azithromycin for the Prevention of Exacerbations of COPD [MACRO] study; 885 from the previously conducted Simvastatin in the Prevention of COPD Exacerbations [STATCOPE] study) were screened for inclusion. Criteria included clinical diagnosis of moderate to severe COPD, a >10 pack-year smoking history, and supplemental oxygen treatment or COPD exacerbation within the year prior to enrollment.

Cardiovascular risks were calculated using the Adult Treatment Panel III; participants receiving statin therapy or with 10-year coronary heart disease risk >20% were excluded from the study. Seasons were defined as winter (December to February), spring (March to May), summer (June to August), and fall (September to November). Regions with < 35 participants were excluded from the study.


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A total of 2179 COPD exacerbations occurred in 787 individuals  (mean age, 63.3), with the winter and spring seasons yielding the highest overall exacerbation rates (0.13 events per person-month and 0.11 events per person-month, respectively; P ≤.001). Although the summer season yielded the lowest overall exacerbation rate, 43% of exacerbations during summer were moderate to very severe, the highest percentage of all the seasons (34.8%, 32.1%, and 31.9% respectively in the spring, fall, and winter; P =.001).

The highest COPD exacerbation rates during winter occurred in the Great Lakes and Northeast regions (0.19 and 0.15, respectively). During spring, the highest COPD exacerbation rates occurred in the Great Lakes and Upper Midwest regions (0.15 and 0.12, respectively). These regions experience the coldest seasonal temperatures during winter and spring compared to other regions in the United States and parts of Canada. The highest COPD exacerbation rate during summer and fall occurred in the West (0.59 and 0.69, respectively). Some regions contained more participants than others (eg, the Great Lakes, n=99 vs the Northeast, n=419).

The primary outcome of the study was COPD exacerbation rate (severely increased, or > 2, of the following symptoms: cough, sputum, wheezing, dyspnea, or chest tightness). Secondary outcomes included exacerbation severity, mortality, treatment with antibiotics or steroid for >2 days, and time (number of days) to first exacerbation in each region and season. COPD exacerbation rates were measured as events/person-month (event rate), and adjusted rates ratios (RR; adjusted for age, gender, forced expiratory volume in 1 second, oxygen use, smoking status, and body mass index) were calculated using summer season RR values as the denominator.

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The authors explained that one major limitation to the study was their exclusion of several participants from the initial screening due to the inability to assess cardiovascular risk factors retrospectively. However, this exclusion was necessary to ensure that participants included in the study did not also have comorbid cardiovascular disease.

The researchers concluded that this study is one of several to describe climate and environmental factors on COPD exacerbation rates and severity, and it may serve as  a stepping stone to understanding regional access to COPD care.

Disclosures: Multiple authors declared affiliations with the pharmaceutical industry. Please refer to reference for a complete list of disclosures.

Reference

So JY, Zhao H, Voelker H, et al. Seasonal and regional variations in COPD exacerbation rates in adults without cardiovascular risk factors [published online July 31, 2018]. Ann Am Thorac Soc. doi:10.1513/AnnalsATS.201801-070OC