Fungal Matters: ITS Sequencing Supports the Need for Regional Fungal Baselines for ERMI and Identifies WHO Fungal Priority Pathogen Taxa in Homes of Older Adults Receiving Home‐ and Community‐Based Services

Older adults face compounded indoor exposure risk due to age‐associated immune decline, higher rates of chronic respiratory disease, and disproportionate time spent at home, yet their residential environments remain understudied. To address this gap, chemical, physical, and biological indoor air quality parameters were characterized in 42 homes of older adults receiving community‐based care in Pittsburgh, Pennsylvania. PM _2.5 , CO ₂ , temperature, relative humidity, and radon were measured continuously; total fungi, bacteria, and nontuberculous mycobacteria were quantified using droplet digital PCR; Environmental Relative Moldiness Index (ERMI) scores were externally processed; and fungal community structure was assessed by ITS amplicon sequencing. Elevated PM _2.5 and radon exposures were prevalent across the cohort. Microbial concentrations and ERMI values were strongly seasonal, with summer sampling associated with peak fungal and bacterial burden. ERMI was strongly correlated with Aspergillaceae relative abundance, with Aspergillus identified as the sole taxon driving score variation after correction, and ERMI scores were not significantly associated with self‐reported water damage or visible mold, suggesting that elevated values reflect a regional Ascomycota‐dominated ecological baseline rather than active contamination. These results demonstrate that ERMI is functioning as designed taxonomically but that interpretation thresholds require regional calibration in Ascomycota‐rich housing environments. Beyond community‐level characterization, ITS sequencing also enabled screening against the World Health Organization Fungal Priority Pathogens List, which identifies 19 fungal species of greatest global concern, ranked by antifungal resistance burden, mortality, and unmet clinical need; ITS sequencing confirmed four of these species in residential settled dust, including Aspergillus fumigatus and Candida parapsilosis , with direct implications for home‐based care of immunocompromised older adults. These findings underscore the importance of regional ecological baselines when interpreting ERMI and highlight the presence of clinically relevant fungal pathogens in the residential environments of aging populations.