Short-term effects of air pollution in a cohort of patients with chronic obstructive pulmonary disease

Abstract

Background: Although damage to the respiratory system from air pollutants has been recognized, research on susceptibility to air pollution in patients with chronic obstructive respiratory disease (COPD) has produced contradictory results. We studied the short-term effects of particulate matter (PM10, PM2.5), nitrogen dioxide (NO2), and ozone (O3) on cardiac and respiratory mortality in a COPD cohort. We assessed age, sex, and previous diseases as effect modifiers.

Methods: Using hospital data (1998-2009) and pharmaceutical data (2005-2009), we enrolled 145,681 COPD subjects, aged 35+ years and residents of Rome, and followed them from 2005 to 2009. A comparison group of people without COPD (1,710,557 subjects) was also studied. We analyzed deaths due to all natural causes (International Classification of Diseases - Ninth Revision codes 1-799). Statistical analyses were carried out using Poisson regression and a case-crossover approach.

Results: PM10, PM2.5, and NO2 (0- to 5-day lag) were associated with daily mortality, with stronger effects in people with COPD. The mortality associated with PM10 (per interquartile range [IQR] = 16 μg/m) was five times more in COPD patients (3.5% [95% confidence interval = -0.1% to 7.2%]) than in other subjects (0.7% [-0.8% to 2.2%]). Effects on respiratory mortality among COPD subjects were particularly elevated from PM2.5 (IQR = 11 μg/m) (11.6% [2.0% to 22.2%]) and NO2 (IQR = 24 μg/m) (19.6% [3.5% to 38.2%]). Older age, male sex, preexisting heart conduction disorders, and cerebrovascular diseases were associated with stronger effects in COPD subjects.

Conclusions: COPD patients are more susceptible to air pollutants, especially PM10 and NO2. These results suggest a need for more protective air pollution standards for susceptible groups.