Sainte Sigolene

The objective of this clinical trial is to determine whether ultraviolet germicidal irradiation (UVGI) can decrease the frequency of severe acute respiratory infections in elderly people living in nursing homes. 12 elderly nursing homes (ENH) will participate in the study. In all the ENHs included, UVGI devices will be installed in upper part under the ceiling of common rooms (refectories, group activity rooms, lounges) at the start of the study. The UVGI devices can be deactivated by installing an invisible internal filter. The inactivation filters will be installed by a technical team independent of the investigation team. Inactivation will therefore be carried out blind to the care givers and the investigation team. The nursing homes included will be randomized into two arms: * In arm A: the UVGI device will be left active during period 1, and filtered/deactivated during period 2. * In arm B: the UVGI device will be filtered/deactivated during period 1 and left active during period 2. The two periods will last 7 months each, and will take place two years in a row on the same dates (October 1 to April 30). They will be separated by a 5-month wash-out period (May 1 to September 30), during which all UVGI devices will be switched off in both arms. The main questions the study aims to answer is: do active UVGI devices decrease the number of acute respiratory infections leading to oxygen therapy, hospitalization or death during the study periods.