Abstract
RATIONALE: Fine particulate matter air pollution of 2.5 μm or less in diameter (PM(2.5)) has been associated with an increased risk of respiratory disease, but assessments of specific respiratory infections in adults are lacking. OBJECTIVES: To estimate the rate of respiratory infection healthcare encounters in adults associated with acute increases in PM(2.5) 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 relative rate of healthcare encounters associated with increases in PM(2.5) in the previous 1-7 days and explored differences before (2005-2007), during (2008-2013), and after (2014-2016) implementation of air quality policies and economic changes. RESULTS: Interquartile range increases in PM(2.5) over the previous 7 days were associated with increased excess rates (ERs) of culture-negative pneumonia hospitalizations (2.5%; 95% confidence interval [CI], 1.7-3.2%) and ED visits (2.5%; 95% CI, 1.4-3.6%), and increased ERs of influenza ED visits (3.9%; 95% CI, 2.1-5.6%). Bacterial pneumonia hospitalizations, but not ED visits, were associated with increases in PM(2.5) 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 with the "during" period, despite reductions in overall PM(2.5) concentrations. CONCLUSIONS: Increased rates of culture-negative pneumonia and influenza were associated with increased PM(2.5) concentrations during the previous week, which persisted despite reductions in PM(2.5) from air quality policies and economic changes. Though unexplained, this temporal variation may reflect altered toxicity of different PM(2.5) mixtures or increased pathogen virulence.