Respiratory viruses are frequently responsible for acute respiratory failure which justifies hospitalization in intensive care unit. Actually, recent epidemics of emerging viruses (including COVID-19) have highlighted the possibility of air-type transmission in this specific population. Despite the fact that the risk of environmental contamination has never been objectified, It is probable that in intensive care patients, this contamination is greater than in other patients because of the gravity of the patients (greater inoculum) and the use of ventilation techniques responsible for probably increased exhaled viral expression. Defining the mode of transmission of respiratory viruses has major consequences in terms means of prevention. The "air" mode of transmission absolutely requires hospitalization in a single room and sometimes additional air treatment. The droplet transmission mode due to its short range requires simpler measures (wearing a surgical mask, no specific air treatment) and has also led to the discussion of the value of the individual room. Indeed, the use of high flow ventilation system such as "optiflow" or non-invasive ventilation, can transform a droplet risk into "air" risk. For this reason, measuring the extent of environmental contamination around infected patients in intensive care is a major issue.
