Effect measure modification of the association between short-term exposures to PM(2.5) and hospitalizations by longs-term PM(2.5) exposure among a cohort of people with Chronic Obstructive Pulmonary Disease (COPD) in North Carolina, 2002–2015

BACKGROUND: Approximately nine million adults in the United States are living with chronic obstructive pulmonary disease (COPD), and positive associations between short-term air pollution exposure and increased risk of COPD hospitalizations in older adults are consistently reported. We examined the association between short-term PM(2.5) exposure and hospitalizations and assessed if there is modification by long-term exposure in a cohort of individuals with COPD. METHODS: In a time-referent case-crossover design, we used a cohort of randomly selected individuals with electronic health records from the University of North Carolina Healthcare System, restricted to patients with a medical encounter coded with a COPD diagnosis from 2004–2016 (n = 520), and estimated ambient PM(2.5) concentrations from an ensemble model. Odds ratios and 95% confidence intervals (OR (95%CI)) were estimated with conditional logistic regression for respiratory-related, cardiovascular (CVD), and all-cause hospitalizations. Exposures examined were 0–2 and 0–3 day lags of PM(2.5) concentration, adjusting for daily census-tract temperature and humidity, and models were stratified by long-term (annual average) PM(2.5) concentration at the median value. RESULTS: We observed generally null or low-magnitude negative associations with short-term PM(2.5) exposure and respiratory-related (OR per 5 µg/m(3) increase in 3-day lag PM(2.5): 0.971 (0.885, 1.066)), CVD (2-day lag: 0.976 (0.900, 1.058) and all-cause (3 day lag: 1.003 (0.927, 1.086)) hospitalizations. Associations between short-term PM(2.5) exposure and hospitalizations were higher among patients residing in areas with higher levels of annual PM(2.5) concentrations (OR per 5 µg/m(3) in 3-day lag PM(2.5) for all-cause hospitalizations: 1.066 (0.958, 1.185)) than those in areas with lower annual PM(2.5) concentrations (OR per 5 µg/m(3) in 3-day lag PM(2.5) for all-cause hospitalizations: 0.914 (0.804, 1.039)). CONCLUISONS: Differences in associations demonstrate that people in areas with higher annual PM(2.5) exposure may be associated with higher risk of hospitalization during short-term increases in PM(2.5) exposure. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12940-023-00999-4.