Effect measure modification of the association between short-term exposures to PM2.5 and hospitalizations by longs-term PM2.5 exposure among a cohort of people with Chronic Obstructive Pulmonary Disease (COPD) in North Carolina, 2002–2015
Approximately nine million adults in the United States are living with Chronic Obstructive Pulmonary Disorder (COPD), and 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 PM2.5 exposure and hospitalizations and potential modification by long-term exposure in a cohort of individuals with COPD. 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 PM2.5 concentrations from an ensemble model. Odds Ratios and 95% confidence intervals (OR (95%CI)) were estimated with logistic regression for respiratory-related, cardiovascular (CVD), and all-cause hospitalizations. Exposures examined were 0-2 and 0-3 day lags of PM2.5 concentration, adjusting for daily census-tract temperature and humidity, and models were stratified by long-term (annual average) PM2.5 concentration. We observed generally null or low-magnitude negative associations with short-term PM2.5 exposure and respiratory-related (OR for 5 µg/m3 increase in 3-day lag PM2.5: 0.970 (0.889, 1.060)), CVD (0.973 (0.901, 1.049) and all-cause (0.999 (0.927, 1.075)) hospitalizations. Associations between short-term PM2.5 exposure and hospitalizations were higher among patients residing in areas with higher levels of annual PM2.5 concentrations than those in areas with lower annual PM2.5 concentrations. Differences in associations demonstrate that people in areas with higher annual PM2.5 exposure may be associated with higher risk of hospitalization during short-term increases in PM2.5 exposure.