The association between indoor airborne bacteria and allergic respiratory diseases - a Northern European study

Introduction: Allergic diseases are on the rise and affect myriads of people worldwide. While studies have suggested a diverse and abundant airborne microbiome to reduce the risk of allergic respiratory diseases in children, this link has not yet been established in adults. Aim and objective: We aimed to investigate the association between the indoor airborne microbiome and allergic respiratory diseases in adults. We hypothesized that decreased microbial diversity and load would be associated with a higher prevalence of allergic respiratory diseases. Methods: Settled dust were collected from the bedroom of 1038 participants from the follow-up of the European Community Respiratory Health Survey, ECRHS III (2011-2014). The dust samples were analyzed for microbiome composition and load by 16S rRNA sequencing and qPCR. Information on diseases was derived from questionnaires. Analyses were stratified by atopic status (from specific IgE and skin prick tests), and performed using logistic regression, adjusted for sex, age, smoking, and study centre. Results: An increase in bacterial load was found to be associated with more asthma, both allergic (OR per IQR 1.12 (1.02-1.25) and non-allergic (1.13 (1.03-1.24)). The same was seen for non-allergic rhinitis (1.13 (1.02-1.27)), whereas an opposite association was seen for allergic rhinitis (0.98 (0.89-1.07)). These results were not found for bacterial richness or Shannon Index. There were no significant association between the microbial indices and chronic rhinosinusitis, current asthma, or atopic status. Conclusion: The results suggest a link between bacterial load and allergic diseases for adults. The results were, however, not consistent.