Time-to event analyses for hospital stay: Nosocomial infections influence the length of stay for infections caused by respiratory viruses

Nosocomial transmission of respiratory viruses can contribute to increased morbidity and mortality and should therefore be prevented by preventive measures. In the present study, the extent to which nosocomial transmission influences the length of hospitalisation of patients was systematically investigated

Methods: In a retrospective monocentric analysis over 5 years, all hospitalised patients with evidence of influenza A, B, RSV and SARS-CoV-2 (original strain / Omicron) were included. Demographic data (age, sex), risk factors (COPD, diabetes, kidney desease, heart disease, cancer) and clinical course were recorded. Definitions were used to differentiate between nosocomial and community-acquired (CA) infections. A restricted mean survival time (RMST) (survival event is normal discharge) was used to calculate the influence of variables on the length of hospitalisation; the effects of each variable were compared by comparing Hazard Ratio (HR) and 95% CI. Deceased patients were excluded for the RMST / HR because of the bias problem on hospital stay.

Results: A total of 2269 patients with specific virus detection were included, 263 of whom were defined as nosocomial. The hospitalisation times for patients with nosocomial infections compared to CA infections were significantly higher at 23.4 vs. 10.4 days (p < 0.001) (differentiated by specific virus detection: Infl. A: 20.5 vs. 9.2 (p < 0.001) / Infl. B 17.9. vs. 8.2 (< 0.001) / RSV 24.6 vs. 10.7 (< 0.001) / SARS-CoV-2 26.4 vs. 15.5 (0.497) / Omicron 25.5. vs. 9.64 (< 0.001)). For patients with evidence of influenza A / B, RSV, SARS-CoV-2 and Omicron, the effect of a nosocomial infection on the length of stay was significant (HR = 0.52 (SARS-CoV-2) and HR < 0.5). Other factors in individual virus detections with a significant influence on the length of hospitalisation were age, diabetes and a bacterial superinfection.

Conclusion: Nosocomial infections have a significant impact on the length of stay and discharge of patients with specific viral infections. Preventive measures must therefore enforced in the management of patients with respiratory infections in order to prevent nosocomial infections.