Gut and respiratory tract microbiota in children younger than 12 months hospitalised for bronchiolitis compared with healthy children. Can we predict the severity and medium-term respiratory outcome?

Abstract Background: Growing evidence indicates that infant microbiota has a potential key effect on bronchiolitis. However, little is known about the potential factors, such as the presence of respiratory syncytial virus (RSV) and viral coinfection, in both the gut and respiratory tract microbiota of children younger than 12 months hospitalised for bronchiolitis compared with children with no identified viruses and with healthy children. Methods: This was a case control, multicentre, prospective study in 2 hospitals (Severo Ochoa University Hospital and La Paz University Hospital) that included 96 infants (57 cases and 39 controls). Gut (faeces) and respiratory (nasopharyngeal aspirate [NPA]) microbial profiles were analysed by 16S rRNA gene sequencing, and respiratory viruses were identified by targeted multiplex reverse transcription-polymerase chain reaction assays. Clinical data of the acute episode, respiratory morbidity and follow-up during the first year after infection were recorded. Results: 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 in the year 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. Conclusions: A distinct respiratory and intestinal microbiota pattern was observed in infants with bronchiolitis compared with healthy controls. The presence of RSV was a main factor as a catalyst for dysbiosis. Lower gut microbial richness and increased respiratory microbial diversity were observed in the infants with respiratory morbidity during follow-up.