Outcomes Related to Bacterial Co-Infection and Antibiotic Use in Adults Hospitalized With Respiratory Syncytial Virus Compared with Influenza

Sep 28, 2026

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Multicenter cohort evidence evaluates whether bacterial co-infection and antibiotic use influence mortality and major clinical endpoints among adults hospitalized with respiratory syncytial virus (RSV) versus influenza A or B. Microbiological testing defined bacterial co-infections, while antibiotic exposure within 48 hours was assessed alongside pneumonia burden, high-flow oxygen, mechanical ventilation, and length of stay. In adjusted models, bacterial co-infection in RSV patients showed no association with mortality at 14, 30, or 90 days or other adverse outcomes. Early antibiotics prolonged length of stay without improving survival.

LanguageEnglish

CategoryHealthcare

FormatPDF

Pages8

Reading Time20 min

AccessFree to download

Background

Methods

Results

Conclusions

Open Forum Infectious Diseases MAJOR ARTICLE Outcomes Related to Bacterial Co-Infection and Antibiotic Use in Adults Hospitalized With Respiratory Syncytial Virus Compared with Influenza Kristine L. Karlsen,1 Clara L. Clausen,1, Ragda A. S. Kahiyah,2 Aymen Alkarawi,2 Amanda M. Egeskov-Cavling,2, Noor Hayder,2 Adin Sejdic,2 Casper Roed,2,3 Jon G. Holler,2, Lene Nielsen,4, Mads F. Eiberg,2 Omid Rezahosseini,2, Christian Østergaard,5 Zitta B. Harboe,2,3,6 Thea K. Fischer,7,8 Birgitte Lindegaard,2,3,a, and Thomas Benfield1,a, 1Department of Infectious Diseases, Center of Research and Disruption of Infectious Diseases (CREDID), Amager and Hvidovre Hospital, Copenhagen, Denmark, 2Department of Pulmonary and Infectious Diseases, Copenhagen University Hospital, North Zealand Hospital, Hilleroed, Denmark, 3Department of Clinical Medicine, Faculty of Health and Medical Science, University of Copenhagen, Copenhagen, Denmark, 4Department of Clinical Microbiology, Herlev and Gentofte Hospital, Copenhagen, Denmark, 5Diagnostic Infectious Disease Preparedness, Statens Serum Institut, Copenhagen, Denmark, 6Department of Bacteria, Parasites, and Fungi, Statens Serum Institut, Copenhagen, Denmark, 7Department of Clinical Research, Copenhagen University Hospital, North Zealand Hospital, Hilleroed, Denmark, and 8Department of Public Health, University of Copenhagen, Copenhagen, Denmark Background. Adults hospitalized with respiratory syncytial virus (RSV) face mortality risks comparable to or higher than those with influenza A or B. However, studies on the impact of bacterial co-infections on mortality are inconsistent. Methods. This multicenter cohort study included adults hospitalized with RSV, influenza A, or B over 3 years at two tertiary care hospitals. Microbiological testing, bacterial co-infections, antibiotic use, and their association with clinical outcomes were analyzed using adjusted linear and logistic regression models. Results. Of 986 patients, 352 (36%) had RSV, 347 (35%) influenza A, and 287 (29%) influenza B. The median age was 74 years, 54% were women, and 76% had at least one comorbidity. Overall, 32% had pneumonia. The prevalence of bacterial co-infections was comparable across patients with RSV (23%), influenza A (25%), and B (28%). Among patients without bacterial co-infection, antibiotic use within 48 hours remained common across all virus groups (77%, 71%, and 75%, respectively) . In adjusted analyses, bacterial co-infection in patients with RSV was not associated with mortality at 14, 30, or 90 days, high-flow oxygen therapy, mechanical ventilation, or length of stay (LOS) . Early antibiotic treatment was associated with prolonged LOS but not improved survival. Conclusions. Bacterial co-infections were identified in approximately one-quarter of patients with RSV, influenza A, and B. Among patients with RSV, bacterial co-infection was not associated with adverse clinical outcomes, and early antibiotic treatment did not appear to improve clinical outcomes. Keywords. antibiotic treatment; bacterial co-infections; clinical outcomes; influenza; respiratory syncytial virus. In the European Union it is estimated that an average of 158 229 Respiratory Syncytial Virus (RSV)-associated hospitalizations in adults occur annually [ 1] . Studies from Europe, the USA, and Asia have shown that adults hospitalized with RSV have similar or higher mortality risk compared with Received 28 September 2025; accepted 09 December 2025; published online 18 December 2025 aB. L. and T. B. share the last position. Correspondence: Kristine Lilhammer Karlsen, BSc, Department of Infectious Diseases, Center of Research and Disruption of Infectious Diseases (CREDID), Amager and Hvidovre Hospital, Kettegård Alle 36, 2650 Hvidovre, Copenhagen, Denmark (kristine. lilhammer. [karlsen.01@regionh.dk](karlsen.01@regionh.dk)) . Open Forum Infectious Diseases® © The Author(s) 2025. Published by Oxford University Press on behalf of

FAQs

How was bacterial co-infection assessed in hospitalized adults?

Microbiological testing identified bacterial co-infections, which were then compared across RSV, influenza A, and influenza B patient groups.

Did bacterial co-infection affect mortality in RSV patients?

In adjusted analyses, bacterial co-infection among RSV patients was not associated with mortality at 14, 30, or 90 days.

What was the impact of early antibiotic treatment?

Early antibiotic treatment was associated with prolonged length of stay but did not improve survival.

Sep 28, 2026

Uploaded by Mimi