Evaluation of the lower airway microbiota in patients with severe sars-cov2

ABSTRACT

RATIONALESecondary infections with bacterial pathogens are thought to be responsible for poor outcomes in the 1918 Spanish and H1N1 pandemics. We postulate that poor prognosis in patients with SARS-CoV2 may be associated with uncontrollable viral replication, co-infection with a secondary pathogen, and over exuberant host immune response. We seek to evaluate whether there is an association between distinct features of the lower airway microbiota and poor clinical outcome in patients with SARS-CoV2. METHODS:We collected lower airway samples in 148 patients from NYU admitted between 3/10/2020 and 5/10/2020 with severe respiratory failure requiring mechanical ventilation and that underwent bronchoscopy for airway clearance and/or tracheostomy. Clinical outcome was defined as dead vs alive. DNA was isolated in parallel using zymoBIOMICS™ DNA/RNA Miniprep Kit (Cat R2002) as per manufacturer's instructions. The V4 region of the 16S rRNA gene marker was sequenced using Illumina MiSeq. Sequences were analyzed using the Quantitative Insights into Microbial Ecology (QIIME version 1.9.1) pipeline. Total bacterial load was evaluated in lower airway samples using digital droplet PCR targeting the 16S rRNA gene. RESULTS:Of the 148 patients included, 114 survived (77%) and 34 (23%) died. Among those with poor clinical outcome, there was a non-statistically significant trend towards higher age and BMI. Patients who died more commonly had chronic kidney disease and prior cerebrovascular accidents, and more often required dialysis. There was no statistically significant difference in the rate of positive bacterial respiratory or blood cultures among those that survived vs. those that died (75 vs. 73% and 43 vs 38%, respectively). Topographical analysis of the 16S RNA microbiome shows compositional differences between the upper and lower airways based on β diversity comparisons. When comparing across clinical outcomes, the α diversity was lower in the dead group but there was no statistically significant difference in overall community composition (β diversity). Taxonomic differential enrichment analysis using DESeq analysis showed that oral commensals were enriched in the group that survived. Patients that died had a higher bacterial load in their lower airways than those who survived. CONCLUSION:Using samples obtained via bronchoscopy we identified lower airway microbiota signatures associated with mortality among critical patients infected with SARS-CoV2. Taxonomic signals identified as associated with poor prognosis did not reveal bacterial taxa commonly classified as respiratory pathogens. This data is not supportive of the hypothesis that secondary untreated bacterial co-infections are responsible for increased mortality in patients with severe SARS-CoV-2.