2018 Yes https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6138906/ Nygaard, Anders B Europe Exposure Study Modeling Elementary (K-5) Kindergartens Indoor microbiome Dust analysis Antibiotic resistance Built environment Significant changes in the microbial community composition were observed over time (PERMANOVA, P < 0.05). Particularly, changes in the abundance and the proportions of human associated bacteria were found. A decrease in the prevalence of Propionibacterium from over 16% abundance to less than 1% and an increase in Streptococcus from 10 to 16% were the most significant findings. Four classes of clinically relevant antibiotic resistance genes were tested for; three were detected in the dust, indicating the presence of resistant bacteria and a potential for resistance spread. Petrifilm analysis showed that some surfaces in the kindergarten were of consistent poor hygienic quality, and new hygienic routines are required.