Abstract / Summary
Abstract Background: Environmental factors influence respiratory virus transmission, but the role of outdoor fungal spores in tropical environments remains poorly characterized. We examined associations between fungal spore concentrations and influenza and SARS-CoV-2 incidence in Puerto Rico, and conducted exploratory virus-specific mortality analyses. Methods: We conducted a retrospective ecological time-series study in two Puerto Rican health regions (San Juan/Metro and Caguas) from 2022 to 2024. Daily fungal spore and pollen concentrations from two National Allergy Bureau stations were linked to laboratory-confirmed case counts. Analyses included seasonal correlations, logistic regression of daily high-incidence status, random forest classification, and exploratory region-specific negative binomial mortality models, all adjusted for season. Results: Fungal spores correlated with influenza and SARS-CoV-2 incidence in fall across all four region–virus combinations (r = 0.19–0.35, p < 0.001). Influenza associations strengthened at 2–4-day lags, whereas SARS-CoV-2 associations peaked at or near lag 0. Higher fungal, but not pollen, concentrations were associated with increased odds of top-quartile incidence days in every region–virus combination (odds ratio 1.12–1.34 per 10,000 spores/m³, p < 0.001). Random forest classifiers using fungal spores alone showed high apparent discrimination in randomly split fall data. In exploratory mortality analyses, only influenza mortality in Caguas was conventionally associated with fungal concentration (incidence rate ratio 1.17, 95% confidence interval 1.03–1.33, p = 0.016); it did not survive Bonferroni correction, and the remaining models were null. Conclusions: Outdoor fungal spores showed modest associations with the incidence of both viruses in both regions during 2022–2024. Future studies will integrate meteorological variables and prospectively validate these associations.