Manipulating the infant respiratory microbiomes to improve clinical outcomes: A review of the literature

Background: The association between infant respiratory microbiota and disease (including respiratory tract infections and asthma) is increasingly recognised, although the mechanism remains unclear. Respiratory infections and asthma account for a large proportion of infant morbidity and mortality, so the possibility of preventing disease or modifying clinical outcomes by manipulating microbiome development warrants investigation. Objectives and methods: We identified studies that investigated the efficacy of live bacteria (probiotics or human challenge) or their substrates to modify respiratory colonisation or clinical outcomes in infants. Eligibility criteria: Interventional studies involving infants under one year of age, administration of live bacteria or their substrates, and outcome measures including bacterial colonisation, microbiome profile, or respiratory disease phenotypes. Results and limitations: Some bacterial interventions can reduce infant respiratory infections, although none have been shown to reduce asthma incidence. The literature is heterogeneous in design and quality, precluding meaningful meta-analysis. Conclusions: Upper respiratory tract infant microbiome manipulation may alter outcomes in respiratory tract infection, but further well-conducted research is needed to confirm this. Improved regulation of proprietary bacterial products is essential for further progress. (C) 2021 The British Infection Association. Published by Elsevier Ltd. All rights reserved.