Water–Vapor treatment of Shower Systems in healthcare facilities: An effective protocol to contain the risk of exposure to Legionella of at-risk patients

Legionnaires' disease (LD) causes severe pneumonia with 5-15?se fatality rates in hospitalized patients, with rising incidence across Europe, North America and Japan. While established disinfection protocols exist for building pipes, no large-scale solution addresses shower systems themselves, where point-of-use filters remain impractical for widespread implementation. We assessed an effective protocol to contain Legionella proliferation from terminal water outlets in healthcare facilities, nursing homes, and high-risk residences. We evaluated an innovative water-vapor protocol consisting of sequential water flushing followed by high-pressure vapor at 120℃. Biofilms were grown under controlled conditions across five settings—one healthcare facility, one nursing home, and three private residences—targeting biofilms aged 5-104 weeks during peak LD season. Efficacy was assessed through scanning electron microscopy, flow cytometry, 16S rRNA sequencing, and functional pathway analysis (PICRUSt2), comparing results with conventional thermal disinfection (65℃, 10 minutes) and untreated controls.