Factors influencing antibiotic use in confirmed viral respiratory tract infections

The use of antibiotic therapy in confirmed viral respiratory tract infections is controversial, with discordance amongst guidelines.

We evaluated antibiotic usage in patients admitted with confirmed influenza A, respiratory syncytial virus and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections, as well as factors associated with their initiation and duration.

This was a prospective observational cohort study of patients admitted to a tertiary centre with PCR-confirmed viral respiratory tract infection. Patient characteristics, antibiotic use, choice, route and duration, as well as patient outcomes were measured. Clinical and microbiological factors related to the admission were recorded. Multivariate regression analyses were used to identify factors associated with antibiotic initiation and duration.

There were 241 admissions with confirmed viral respiratory tract infections over the 2025/26 winter period. Antibiotic therapy was commenced in 208 (86%) cases, with a median 7 days of therapy given. Additional cultures were taken from 159, with positive bacterial cultures in 35 (35/159, 22%). A requirement for supplemental oxygen (OR 4.61, P = 0.02) and increased C-reactive protein at admission (OR 1.03, P < 0.001) were associated with increased likelihood to commence antibiotics, while ongoing supplemental oxygen requirement (β coefficient 0.41, P = 0.005) was associated with increased duration of antibiotic therapy. Antibiotic duration was not influenced by bacterial culture results.

We demonstrate high rates of antibiotic usage in patients admitted with confirmed viral respiratory tract infection, and identify opportunities for improved antimicrobial stewardship.