Hospital-acquired Viral Respiratory Infections (HAVRI) are associated with substantial burden on health care systems. The prevention and control of these viral infections rely on multiple measures such as hand hygiene or wearing mask. However, vaccination remains the major preventive measure. To date, data at French national level are insufficient to describe the epidemiology of these infections, including their burden, and the potential protection of patients if vaccination coverage of health care professionals/patients is satisfactory. In addition, better understanding of the clinical characteristics of HAVRI will make it possible to identify potential sources of transmission as soon as possible and to implement appropriate hygiene measures. We will set up a hospital-based prospective multicenter study in Bordeaux, Paris-Bichat, Dijon and Lyon, involving four inclusion services (geriatrics, internal medicine and transplantation) per hospital. The main objective of this study is to calculate the incidence rate of hospital-acquired infections for three respiratory viruses; influenza, SARS-CoV-2 and syncytial respiratory virus (SRV), referred to as HARVI, in participating services. Volunteered health care professionals or hospitalized patients presenting with influenza-like illness (ILI) at admission or during their stay in the participating centers will be eligible to be enrolled during the two inclusion periods: (mid-October 2024 to mid-April 2025 and mid-October 2025 to mid-April 2026). For each patient/health care professional, a nasopharyngeal swab will be collected. A questionnaire including demographic data, medical history, vaccination, and clinical and biological data of the viral episode will also be completed by the study team. Patients tested positive for one of the viruses studied will be considered cases and patients tested negative as controls. The collected data will be pseudonymized before statistical analyses. Statistical analyses will consist of calculating incidence rates, attack rates overall and by causative virus and analysis of factors associated with the occurrence of HARVI. The prospective design of the study will optimize the quality of the collected data (ex. consolidate the documentation of both the clinical picture and vaccination in patients and health care professionals by reducing memory bias) and allow to calculate the incidence rates, the crude and adjusted relative risks of HARVI according to the studied factors, and to describe multiple outcomes (hospitalization in intensive care units, death, etc.) based on the causative virus. The results of this research project will allow to: * obtain epidemiological indicators associated with HARVI; * estimate the impact of HARVI on the prognosis of patients in hospital; * assess the impact of HARVI on the total length of hospital stay; * identify risk factors associated with HARVI; * use the results as an argument for vaccination in order to increase vaccination coverage of healthcare workers.