SPS2-04 Asthma Status Modifies Protective Associations of School Indoor Microbial Richness With Respiratory Outcomes Among School Staff

Rationale

The biodiversity hypothesis posits that host-environment microbial interactions shape human health. However, there is limited evidence on how microbial communities in school environments, where staff spend much of their time, affect their respiratory health. We evaluated associations between school indoor microbial richness and respiratory outcomes among staff, examining asthma status as a potential effect modifier.

Methods

In 2015-2016, we conducted a cross-sectional study in 50 elementary schools in a U.S. city. School staff completed web-based questionnaires reporting 12-month general and building-related respiratory symptoms (defined as improvement away from building). Vacuumed floor dust was collected from 500 classrooms (10/school). Bacterial 16S ribosomal RNA gene and fungal internal transcribed spacer regions were sequenced using Illumina MiSeq and clustered into operational taxonomic units (OTUs) to estimate microbial richness. Exposure was defined as floor-averaged richness for each participant’s workspace. Logistic regression estimated adjusted odds ratios (aORs) for respiratory outcomes, controlling for demographics, smoking status, teaching, ethnicity, dampness/mold, and hay fever. Exposure-response linearity was assessed using generalized additive models (GAMs) and log-likelihood ratio (LR) tests.

Results

Across all 500 samples, bacterial richness (240-659 OTUs) exceeded fungal richness (63-277 OTUs), with Actinobacteria richness significantly higher than Firmicutes (p < 0.001). Among 1,529 participants (51% participation; 94% female, 70% White, 16% current asthma), symptom prevalence ranged from 19% (nocturnal dyspnea) to 86% (stuffy nose), with 51-69% of symptomatic participants reporting building-relatedness. Significant interactions were observed between microbial richness and asthma status for building-related lower and general upper respiratory outcomes (p < 0.05). Among participants without asthma, higher richness of Gram-positive Actinobacteria and Firmicutes was associated with lower odds of wheeze, cough, dyspnea, and hay fever (aORs=0.987-0.993). Among participants with asthma, no associations were observed between this richness and any respiratory outcomes. Conversely, fungal richness was protective primarily among those with asthma: higher total fungal and yeast richness were associated with lower odds of wheeze, chest tightness, and stuffy nose (aORs=0.899-0.989). Gram-negative bacterial richness was protectively associated (aOR=0.996) only with hay fever among non-asthmatics. GAM and LR tests supported linear exposure-response relationships, except for Firmicutes richness and building-related wheeze.

Conclusions

Greater exposure to diverse indoor bacterial communities—particularly Actinobacteria and Firmicutes—was associated with fewer respiratory outcomes among school staff without asthma, but not those with asthma. Conversely, among participants with asthma, greater fungal and yeast diversity was associated with protective effects against respiratory outcomes. Our findings suggest distinct host responses to environmental microbial exposures, reflecting divergent biodiversity hypotheses in asthmatics and non-asthmatics.

This abstract is funded by: NOISH Intramural Public Health Practice Program Funding