The Association between Respiratory Infection and Air Pollution in the Setting of Air Quality Policy and Economic Change

Rationale: Fine particulate air pollution (≤2.5µm; PM2.5) has been associated with an increased risk of respiratory disease, but assessments of specific respiratory infections in adults are lacking. Objective: To estimate the rate of respiratory infection healthcare encounters in adults associated with acute increases in PM2.5 concentrations. Methods: Using case-crossover methods, we studied 498,118 adult New York State residents with a primary diagnosis of influenza, bacterial pneumonia, or culture negative pneumonia upon hospitalization or emergency department (ED) visit (2005-2016). We estimated the rate of healthcare encounters associated with increases in PM2.5 in the previous 1-7 days and explored differences Before (2005 to 2007), During (2008-2013), and After (2014-2016) implementation of air quality policies and economic changes. Results: Interquartile range increases in PM2.5 over the previous 7 days were associated with increased excess rates of culture negative pneumonia hospitalizations (2.5%; 95% CI 1.7%, 3.2%) and ED visits (2.5%; 95% CI 1.4%, 3.6%), and increased excess rates of influenza ED visits (3.9%; 95% CI 2.1%, 5.6%). Bacterial pneumonia hospitalizations but not ED visits were associated with increases in PM2.5 and though imprecise, were of a similar magnitude to culture negative pneumonia (Lag day 6 ER 2.3%; 95% CI: 0.3, 4.3). Increased relative rates of influenza ED visits and culture negative pneumonia hospitalizations were generally larger in the After period (p< 0.025 for both outcomes), compared to the During period, despite reductions in overall PM2.5 concentrations. Conclusion: Increased rates of culture negative pneumonia and influenza were associated with increased PM2.5 concentrations during the previous week, which persisted despite reductions in PM2.5 from air quality policies and economic changes. Though unexplained, this temporal variation may reflect altered toxicity of different PM2.5 mixtures or increased pathogen virulence.