Age- and Period-Stratified Associations Between Ambient Fungal Spore Exposure and Asthma Healthcare Utilization in the San Juan Metropolitan Area, Puerto Rico, 2018–2021

Puerto Ricans experience among the highest asthma morbidity in the United States, and ambient fungal spores are abundant tropical aeroallergens. This ecological time-series study asked whether associations between ambient fungal spores and recorded asthma healthcare utilization in the San Juan Metropolitan Area, Puerto Rico (2018–2021), were stable across two contextual eras (post-Hurricane María recovery, 2018–2019; the COVID-19 pandemic, 2020–2021) and across age groups. Daily Burkard spore counts were linked to 168,578 asthma encounters. Encounter volume (negative binomial rate ratios, RR) and the ED/inpatient encounter fraction (logistic odds ratios, OR) were modeled per 10,000 spores·m−3 using weekly means and 3- and 7-day moving averages, with age adjustment or stratification, period × age interaction tests, false discovery rate (FDR) control, and a time-stratified case-crossover analysis of ED/inpatient events. Age-adjusted annual estimates were close to the null (volume RR 0.990–1.011; fraction OR 0.975–0.999). Associations with the ED/inpatient fraction differed by age and period (interaction p < 0.001), whereas heterogeneity in encounter volume was weak (p = 0.05–0.28). Of 48 period × age estimates, eight were nominally significant, and one survived FDR control (2020, ages 75–84, fraction OR 1.28, 95% CI 1.12–1.47). The 2020 case-crossover estimate for 3-day average exposure was inverse (OR 0.946, 95% CI 0.910–0.984), the 7-day estimate was null, and directions varied across years. These small, heterogeneous associations describe population-level co-occurrence in this region, not individual-level risk.