“Legionnaires’ disease is a multisystem disease which causes pneumonia due to gram-negative bacteria (Legionella spp.) found in freshwater environments around the world. Humans are infected by inhalation of aerosols containing Legionella. The infection can be fatal and outbreaks from a common environmental source can occur. Cases of Legionnaires’ disease are mainly reported in persons in older age groups, especially in males.  Legionellosis is an uncommon form of pneumonia. The disease has no particular clinical features that clearly distinguish it from other types of pneumonia, and laboratory investigations must be carried out to confirm the diagnosis. It normally takes between two to ten days to develop symptoms (typically five to six days) but very rarely some cases may take two to three weeks to develop symptoms.”

European Centre for Disease and Control (https://www.ecdc.europa.eu/en/legionnaires-disease/facts)