Mitigating Legionella spp. risk in an Australian healthcare facility using on-site electrochemical water disinfection

Legionella spp. are Gram-negative bacteria present in natural and engineered water systems that can cause legionellosis (Legionnaires' disease and Pontiac fever). When present in biofilms of healthcare facilities, they are a likely source of legionellosis for immunocompromised patients. The objective of this study was to evaluate an electrochemical water disinfection system to produce and dose hypochlorous acid (HOCl) to reduce this risk in a hospital with systemic Legionella spp. contamination. Furthermore, Legionella spp. colony counts were compared to quantitative polymerase chain reaction (qPCR) results. Before and after implementing the disinfection system, tap water and pipe biofilms were analysed for microbial contamination. Post-implementation monitoring continued for over six months, assessing microbial quality using heterotrophic colony counts, Legionella serotyping, and qPCR targeting total bacteria (16S rRNA) and Legionella spp. By the third sampling event (22 days post-commissioning), water quality consistently improved, with no culture-positive Legionella counts observed thereafter. qPCR analysis confirmed these results, proving more sensitive and reliable than traditional methods. The qPCR assays for Legionella spp. and bacterial 16S rRNA were also cost-effective for system optimisation and diagnostics.