Clinical Impact of Influenza A Coinfection on Staphylococcus aureus Pneumonia during the 2024-2025 Influenza Season in New York City.

Background: Prior studies have emphasized adverse outcomes of bacterial pneumonia, especially due to methicillin-resistant Staphylococcus aureus (MRSA), in patients co-infected with influenza.

Methods: Listings of patients, admitted from an 11-hospital system in New York City, with community-onset pneumonia due to SA were obtained during the winter 2024 and 2025 influenza seasons.

Results: Compared to winter 2024, in 2025 the number of patients admitted with SA pneumonia increased from 55 cases (2.2 patients per 1000 admissions) to 84 cases (3.2 patients per 1000 admissions, P=.03). This increase was driven by influenza-related cases: from 0.28 cases/1000 admissions in 2024 to 1.1 cases/1000 admissions (P=.0005) in 2025. Of the 28 influenza-related cases in 2025, 1) 27 had co-infection with influenza A, 2) 13 were bacteremic, and 3) 15 had methicillin-susceptible SA (MSSA). Patients with MSSA coinfection were more likely to require ICU admission. Only two of the 28 patients had received the seasonal influenza vaccination prior to admission.

Conclusion: During the 2025 influenza season in New York City, there was a significant rise, compared to the 2024 season, of admitted patients with SA pneumonia co-infected with influenza. Nearly half had concomitant bacteremia and patients with MSSA had a more virulent onset of illness.