Indoor air microbiota of pig farms drives the composition of the pig farmer's nasal microbiota in a season dependent and farm specific manner.

Prior studies have demonstrated an influence of the built environment on the human nasal microbiota. However, very little is known about the influences of working on a pig farm on the human nasal microbiota. We longitudinally collected samples from 30 pig farms (air, nasal swabs from humans and pigs) in Switzerland from 2014-2015. As controls, nasal swabs from cow farmers and individuals with no contact with farm animals were included. Analysis of the microbiota for all samples (n=609) was performed based on sequencing (MiSeq) and included the investigations of source-sink dynamics.The number of indoor airborne particles and bacterial load in pig farms was highest in winter. Similarly, the microbiota analyses revealed that the alpha-diversity values of the nares of pig farmers were increased in winter in contrast to samples from the non-exposed controls which displayed low alpha-diversity values throughout the seasons. Source-sink analyses revealed that bacteria from the nose of pigs are more commonly co-identified within the pig farmer's microbiota in winter but to a less extent in summer. In addition, in winter, there was a stronger intra-similarity for samples that originated from the same farm as compared to samples from different farms and this farm-specificity was partially or completely lost in spring, summer and fall.In conclusion, in contrast to non-exposed controls, a pig farmer's nasal microbiota is dynamic as the indoor air microbiota of pig farms drives the composition of the pig farmer's nasal microbiota in a season dependent manner.The airborne microbiota of pig farms poses a potential health hazard and impacts on both livestock and humans working in this environment. Therefore, a more thorough understanding of the microbiota composition and dynamics in this setting is needed. This study has a prospective design (12 months) and uses samples from different sites. This means that the microbiota of air, animals (pigs) and humans has simultaneously been investigated. Our findings highlight that the potential health hazard might be particularly high in winter as compared to summer