Influence of season on exacerbation characteristics in patients with COPD

Patients with COPD experience more frequent exacerbations in the winter. However, little is known about the impact of the seasons on exacerbation characteristics.

Between November 1, 1995, and November 1, 2009, 307 patients in the London COPD cohort (196 men; age, mean, 68.1 years [SD, 8.4]; FEV(1), mean, 1.12 L [SD, 0.46]; FEV(1), mean, % predicted, 44.4% [SD, 16.1]) recorded their increase in daily symptoms and time outdoors for a median of 1,021 days (interquartile range [IQR], 631-1,576). Exacerbation was identified as ≥ 2 consecutive days with an increase in two different symptoms.

There were 1,052 exacerbations in the cold seasons (November to February), of which 42.5% and 50.6% were patients who had coryzal and cough symptoms, respectively, compared with 676 exacerbations in the warm seasons (May to August), of which 31.4% and 45.4% were in patients who had coryzal and cough symptoms, respectively (P < .05). The exacerbation recovery period was longer in the cold seasons (10 days; IQR, 6-19) compared with the warm seasons (9 days; IQR, 5-16; P < .005). The decrease in outdoor activity during exacerbation, relative to a pre-exacerbation period (-14 to -8 days), was greater in the cold seasons (-0.50 h/d; IQR, -1.1 to 0) than in the warm seasons (-0.26 h/d; IQR, -0.88 to 0.18; P = .048). In the cold seasons, 8.4% of exacerbations resulted in patients who were hospitalized, compared with 4.6% of exacerbations in the warm seasons (P = .005).

Exacerbations are more severe between November and February. This contributes to the increased morbidity during the winter seasons.