D26-09 Association Between Ambient PM2.5 Exposure and Daily Asthma Emergency Department Visits in Lima and Callao, Peru (2017-2023): A Time-stratified Case-crossover Analysis

Introduction Exposure to fine particulate matter (PM2.5) has been consistently linked to increased asthma exacerbations. However, this association has not been well characterized in Lima and Callao, densely populated urban areas with persistently elevated air pollution levels. This study evaluated the association between daily ambient PM2.5 exposure and Emergency Department (ED) visits for asthma in these cities from January 1, 2017, to December 31, 2023. Methods We used a time-stratified case-crossover design at the individual level, where each subject served as his or her own control. For each asthma ED visit, the visit day was defined as the case day, and three to four control days were matched by day of the week, month, and year. PM2.5 concentrations at each individual’s residential address were estimated using spatial interpolation based on an exposure model with a 1 x 1 km² spatial and daily temporal resolution. We used conditional logistic regression to estimate odds ratios (ORs) and 95% confidence intervals (CIs), adjusted for ambient temperature, relative humidity, and holidays. Distributed lag non-linear models with natural cubic splines captured lagged and non-linear effects. Effect modification was examined for sex, age, season, district-level socioeconomic status (SES), and residential proximity to major roads. Results The study included 75,602 asthma ED visits and 258,120 control days (within-subject comparisons) from ten Ministry of Health hospitals. PM2.5 exposure was positively and significantly associated with asthma ED visits from lag 0 to lag 13, with the strongest effect on the same day (lag 0). An increase in PM2.5 from 0 to 10, 10 to 20, 20 to 30, 30 to 40, and 40 to 50 µg/m3 was associated with 8.6% (95%CI 1.2%-16.4%), 7.9% (95%CI 1.3%-15.0%), 3.1% (95%CI 1.1%-5.1%), 2.7% (95%CI 0.9%-4.6%), and 4.0% (95%CI 0.1%-8.0%) higher odds of asthma ED visit, respectively, on the same day. Subgroup analyses revealed stronger associations among males (OR = 1.12; 95% CI: 1.01-1.23 for a 0 to 10 µg/m3 increase in lag 0), among children aged 0-9 years (OR = 1.18; 95% CI 1.08-1.29), during the warm season (OR = 1.105; 95% CI: 1.004-1.216), and in higher SES areas (OR = 1.11; 95% CI: 1.04-1.18). Effect estimates declined with increasing lag and higher PM2.5 levels. Conclusions Ambient PM2.5 exposure was associated with increased asthma ED visits in Lima and Callao. The effects were most pronounced on the same day of exposure, particularly among males, young children, residents of higher socioeconomic areas, and with greater vulnerability during the warm season.