Little is known about the relationships between severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the respiratory virus responsible for the ongoing coronavirus disease 2019 (COVID-19) pandemic, and the upper respiratory tract (URT) microbiome.

We sought to compare the URT microbiome between SARS-CoV-2–infected and –uninfected adults and to examine the association of SARS-CoV-2 viral load with the URT microbiome during COVID-19.

We characterized the URT microbiome using 16S ribosomal RNA sequencing in 59 adults (38 with confirmed, symptomatic, mild to moderate COVID-19 and 21 asymptomatic, uninfected controls). In those with COVID-19, we measured SARS-CoV-2 viral load using quantitative reverse transcription PCR. We then examined the association of SARS-CoV-2 infection status and its viral load with the ⍺-diversity, β-diversity, and abundance of bacterial taxa of the URT microbiome. Our main models were all adjusted for age and sex.

The observed species index was significantly higher in SARS-CoV-2–infected than in –uninfected adults (β linear regression coefficient = 7.53; 95% CI, 0.17-14.89; P = .045). In differential abundance testing, 9 amplicon sequence variants were significantly different in both of our comparisons, with Peptoniphilus lacrimalis, Campylobacter hominis, Prevotella 9 copri, and an Anaerococcus unclassified amplicon sequence variant being more abundant in those with SARS-CoV-2 infection and in those with high viral load during COVID-19, whereas Corynebacterium unclassified, Staphylococcus haemolyticus, Prevotella disiens, and 2 Corynebacterium_1 unclassified amplicon sequence variants were more abundant in those without SARS-CoV-2 infection and in those with low viral load during COVID-19.

Our findings suggest complex associations between SARS-CoV-2 and the URT microbiome in adults. Future studies are needed to examine how these viral-bacterial interactions can impact the clinical progression, severity, and recovery of COVID-19.