Long-Term Exposure to Air Pollution and Lower Respiratory Infection in Adults: Evidence From Over 16-Years of Follow-Up for Danish National Cohort

Long-term exposure to air pollution has been linked with acute lower respiratory infections (ALRIs) in children, but the evidence in adults is still mixed and sparse. We aimed to examine the association between long-term exposure to air pollution and recurrent ALRIs in adults.

We followed all adults aged 30 or older (3,083,227) in Denmark for hospital contacts due to ALRIs, pneumonia or influenza from 2000 to 2018. Annual mean concentrations of fine particulate matter (PM2.5), nitrogen dioxide (NO2), and black carbon (BC), in 2010 were modeled using hybrid land-use regression models and assigned to baseline residential addresses. A marginal Cox model was used to assess the association between air pollution and recurrent ALRIs, pneumonia, and influenza. Interaction models were further applied to assess the effect modification by comorbidity and socioeconomic status.

During an average of 16 years’ follow-up, 624,867, 588,491, and 13,260 recurrent events due to ALRIs, pneumonia, or influenza, respectively, were detected. We detected a consistent association between the three pollutants and ALRIs, with hazard ratios (95% confidence interval) of 1.09 (1.09, 1.10) per 10 μg/m3 for NO2; 1.08 (1.08, 1.09) per 0.5 10−5 m−1 for BC, and; 1.04 (1.04, 1.04) per 2 μg/m3 for PM2.5. Such association was stronger in females, non-western immigrants, low-education/income individuals, and patients with prior cardiovascular disease or influenza history. We also detected stronger associations for pneumonia, and a null association for influenza.

Long-term exposure to air pollution may contribute to an increased risk of recurrent ALRIs, particularly pneumonia.