Gut and respiratory tract microbiota in children younger than 12 months hospitalised for bronchiolitis compared with healthy children.

Growing evidence indicates that gut and respiratory microbiota has a potential key effect on bronchiolitis mainly caused by respiratory syncytial virus (RSV). This was a prospective study that comparing infants with bronchiolitis (57 infants) (both RSV and non-RSV associated) to a healthy control group (39 infants) for a total of 96 participants. Gut (faeces) and respiratory (nasopharyngeal aspirate [NPA]) microbial profiles were analysed by 16S rRNA gene sequencing, and respiratory viruses were identified by PCR. Clinical data of the acute episode and follow-up during the first year after infection were recorded. Pairwise comparisons showed significant differences in gut (R2=0.0639, P=0.006) and NPA (R2=0.0803, P=0.006) microbiota between the cases and healthy controls. A significantly lower richness in the intestinal microbiota and an increase in the diversity of the respiratory microbiota (but with an increase in bacteria such as Haemophilus, Streptococcus and Neisseria) were observed in the infants with bronchiolitis, in those with the most severe symptoms and in those who subsequently developed recurrent wheezing episodes after discharge. In NPA, the microbial richness differed significantly between the control group and the non-RSV bronchiolitis group (P=0.01) and between the control group and the RSV bronchiolitis group (P=0.001). In the gut, the richness differed significantly between the control group and the non-RSV group (P=0.01) and between the control group and the RSV bronchiolitis group (P=0.001), with higher diversity in the RSV group.