Tap water as the source of a Legionnaires' disease outbreak spread to several residential buildings and one hospital, Finland, 2020 to 2021.

In Finland, all microbiology laboratories notify findings and physicians notify Legionnaires' disease (LD) cases to the National Infectious Disease Register. All cases are interviewed, and water samples obtained from potential places of exposure. isolates from humans and water are compared by whole genome sequencing (WGS).