More diverse school microbiota may provide better protection against respiratory infections for school staff.

Our understanding of how exposure to school microbiota affects the respiratory health of staff and students in schools is limited. We examined the associations between exposure to school microbiota and respiratory and gastrointestinal infections. We performed an epidemiologic analysis of 1,529 school employees in the U.S. A questionnaire was administered to school staff to collect health information, and floor dust was vacuumed from 500 classrooms in 50 schools. Fungal internal transcribed spacer region and bacterial 16S amplicon sequencing were performed with extracted genomic DNA using Illumina Mi-Seq platform. The resulting DNA sequences were clustered into operational taxonomic units (OTUs). Staff were assigned the school-building-specific floor average number of bacterial or fungal OTUs from the same floor as their exposure. We used logistic regression models to estimate adjusted odds ratios of reported respiratory and gastrointestinal infections in the last 12 months. Exposure to the highest quartile in number of OTUs (Q4, highest richness) of the bacterial phyla Firmicutes or Actinobacteria was associated with 28-61% lower odds of upper or lower respiratory infections compared to the lower three quartiles (Q123). Higher Firmicutes diversity was more strongly associated with upper respiratory infections, while greater Actinobacteria diversity showed a stronger association with lower respiratory infections. Fungal diversity was not associated with any type of infection, and neither bacterial nor fungal diversity was associated with gastrointestinal infections. Our study suggests that exposure to a highly diverse bacterial microbiota in school environments may play an important role in protecting school staff against respiratory infections.