Emerging respiratory diseases represent a global threat. Viruses such as influenza andcoronaviruses have been the main drivers of pandemics over the past century. Morebroadly, the impact of these respiratory infections is not limited to pandemic risks.Indeed, some of them also trigger seasonal epidemics with a significant medical andeconomic burden. Consequently, it is essential to strengthen global surveillance, anddiagnostic capacities for the pathogens responsible for respiratory infections.The diagnosis of respiratory infections is even more important in cases of severeinfection, as it helps guide and adapt patient management according to the responsiblepathogen.A promising and well-recognized approach is the analysis of exhaled breath, whichcontains a complex mixture of volatile organic compounds (VOCs), also known as the"volatilome." The volatilome is influenced by the patient's metabolism, immune system,and microbiome, and can be disrupted by the presence of a pathogen.A parallel clinical study, VORTEX-1, aims to establish the performance of breath analysisfor the diagnosis of respiratory infections in the context of the general population, orpatient triage in emergency wards. This study targets patients with non-severerespiratory infections, mostly caused by viral pathogens.Thanks to a specific technique, the VORTEX-1 study will make it possible to test a directon-site sampling and analysis process, painless and with real-time chemical detection.This methodology, highly suited to triage situations, remains difficult to apply in thecase of respiratory infections requiring hospitalization. Indeed, hospitalized patientsare usually admitted to different units depending on their clinical status, risk factors,or bed availability. This diversity of settings makes it impossible to implement aprocess that depends on an instrument which cannot be available or moved in real timeacross all units. To address this challenge, the investigators will use an alternativemethod.In the VORTEX-2 trial, samples of exhaled gases will be collected directly at thepatient's bedside using a single-use device for breath collection. The samples will thenbe transferred to a laboratory for analysis. This approach is more suitable for severerespiratory infections.To be as comprehensive as possible in the study of the volatilome in the context ofrespiratory infections, it is important to include hospitalized patients and to develop asystem that can also be implemented in routine clinical practice.The link between the two studies (VORTEX-1 and VORTEX-2) will be established through a"control" group, consisting of healthy subjects (without respiratory infections orsevere/chronic diseases), whose breath will be collected using both approaches.