No difference in microbial diversity between bronchoalveolar lavage and tracheal sampling: a systematic review and meta-analysis.

introductionThe respiratory microbiome has a vital role in maintaining respiratory health and preventing pathogen colonisation, but traditional diagnostic methods fail to capture a complete picture of it. Metagenomic sequencing has improved our understanding of microbial ecosystems in both acute and chronic pathologies. However, its results have not been systematically compared between different respiratory sampling techniques, as has been done with traditional methods. Our study aims to compare the microbial diversity in bronchoalveolar lavage (BAL) and tracheal samples using microbiome sequencing.

methodsA systematic search was conducted in Medline, Embase and CENTRAL databases to identify studies where lower respiratory tract microbiome specimens were collected simultaneously using BAL and tracheal sampling and diversity was analysed postsequencing. Risk of bias was assessed with our specifically tailored tool. A random-effects model was used for data synthesis, analysing pooled Shannon, Chao1 and Simpson indices.

resultsWe screened 1050 potentially relevant publications, 10 of which were included. No significant difference was found in microbial alpha diversity between BAL and tracheal samples. The subgroup analysis of tracheal sample types, including sputum and endotracheal aspirate, revealed no significant differences compared with BAL.

conclusionsTracheal sampling methods offer a viable and less invasive alternative to BAL for characterising microbiome alpha diversity in clinical or research settings where segmental sampling is not required. However, further high-quality comparative studies are needed to confirm these findings. PROSPERO REGISTRATION NUMBER: CRD42023436934.