Prevalence and Outcomes of Bacterial Co-detections by Blood Culture Among Children and Adults Hospitalized With Laboratory-confirmed Influenza, Influenza Hospitalization Surveillance Network, 2022–2024

BACKGROUND: Influenza predisposes individuals to bacterial co-infections, which can result in disseminated infection and bacteremia. We describe the epidemiology and outcomes of blood culture co-detections among persons hospitalized with influenza over two influenza seasons. METHODS: We sampled individuals of all ages from FluSurv-NET, a U.S. population-based surveillance network of persons hospitalized with laboratory-confirmed influenza, during the 2022-2023 and 2023-2024 seasons. Surveillance staff collected information on bacterial blood cultures within 3 days before or 3 days following admission. We described patient characteristics and in-hospital outcomes, stratified by culture positivity, number of positive cultures, and type of co-detection, using unweighted counts and weighted percentages to account for the complex survey design. RESULTS: Overall, 14,316 patients were included, with a median (interquartile range) age of 57 (14-74) years, 53.6% female, 52.0% non-Hispanic white, and 25.6% with ≥4 categories of underlying medical conditions. Of these, 50.8% had ≥1 blood cultures obtained and 5.2% overall had ≥1 bacterial co-detections. Intensive care unit admission occurred for 9.6%, 19.2%, 31.2%, and 47.9% among patients with no blood cultures, negative cultures, 1 co-detection, and >1 co-detection documented, respectively; in-hospital mortality occurred in 1.5%, 3.3%, 9.4%, and 14.5%, respectively. Among patients with positive cultures, 22.1% had Staphylococcus aureus and 7.5% had Streptococcus pneumoniae co-detections; both were associated with severe illness (with 22.4% in-hospital mortality each). DISCUSSION: Bacterial co-detections in persons hospitalized with influenza were associated with poor in-hospital outcomes. Efforts to prevent severe influenza and bacterial co-infections, including through vaccination, may reduce substantial morbidity and mortality from influenza.