Prevalence and Predictors of Concomitant Bacterial Infections in Patients With Respiratory Viruses in Ontario: A Cohort Study.

Background: To investigate the prevalence of concomitant bacterial infection across common viral infections.

Methods: This population-based cohort study included patients infected with influenza A and B (FLUA, FLUB) and respiratory syncytial virus (RSV) in Ontario between 2017 and 2019 and patients with SARS-CoV-2 between 2020 and 2021. Specific bacteria present in concomitant infections were identified. Concomitant infections were further classified into different categories (eg, coinfection -2 to +2 days from viral infection and secondary infection >2 days after viral infection). We used logistic regression models to estimate the odds of bacterial infections for FLUA, FLUB, and RSV relative to SARS-CoV-2 while adjusting for confounders.

Results: A total of 4230 (0.5%, 885 004) viral cases had concomitant bacterial infections, encompassing 422 of FLUB (4.7%, 8891), 861 of FLUA (3.9%, 22 313), 428 of RSV (3.4%, 12 774), and 2519 of COVID-19 (0.3%, 841 026). The most prevalent species causing concomitant bacterial infection were Staphylococcus aureus, Streptococcus pyogenes, and Pseudomonas aeruginosa. When compared with SARS-CoV-2, the adjusted odds ratio for bacterial infection was 1.69 (95% CI, 1.48-1.93) for FLUA, 2.30 (95% CI, 1.97-2.69) for FLUB, and 1.56 (95% CI, 1.33-1.82) for RSV. The adjusted odds of coinfection in patients with SARS-CoV-2 were lower but higher for secondary infection as compared with the other viruses.

Conclusions: A higher prevalence and risk of concomitant bacterial infection were found in FLUA, FLUB, and RSV as compared with SARS-CoV-2, although this is largely driven by coinfections. Ongoing surveillance efforts are needed to compare the risk of concomitant infections during periods when these viruses are cocirculating.