Epidemiology of acute respiratory infections in adult patients in Hospices Civils de Lyon, France, between October 2016 and April 2025

Background Multiple viruses can cause acute respiratory infections (ARI), impacting morbidity, mortality and hospital resources. The objective of this study was to describe viral circulation among patients with ARI, patients characteristics and severity outcomes. Methods A retrospective cohort was assembled using electronic health records from the Hospices Civils de Lyon, France. Adult patients (≥18 years) hospitalised or presenting to the emergency department from October 2016 to April 2025 with either an ICD-10 diagnostic code for ARI or a laboratory-confirmed viral detection were included. Administrative variables and laboratory results collected during the stay were extracted. Results 103,011 hospital visits involving 82,077 patients were included. The number of eligible stays increased substantially since the COVID-19 pandemic, along with year-round laboratory testing. Following disruption during the pandemic, winter peaks of ARI incidence, influenza and RSV detections re-emerged after 2022. Influenza, rhinovirus and SARS-CoV-2 positivity rates peaked in younger adults (<65 years), whereas RSV and hMPV positivity rates were highest in patients aged ≥80 years. Patients aged ≥65 years had longer hospitalisations (median 10 vs 8 days, p<0.001), twice in-hospital mortality rate (14% vs 7%, p<0.001), less frequent ICU admission (21% vs 33%, p<0.001) and use of respiratory support than younger adults. Influenza was the virus associated with the shortest length of stays, hMPV was associated with the longest in younger adults. Conclusions Real-world hospital data are valuable for surveillance of viral circulation, early identification of patients at risk of deterioration, and may be used to evaluate the impact of preventive intervention in community.