Paul B Bartley1
1School of Medicine, The University of Queensland, Herston, QLD, Australia. Wesley Private Hospital Auchenflower, QLD, Australia.
Background: Two nosocomial cases of Legionella pneumonia serogroup 1 (LPSG1) occurred at The Wesley Hospital (TWH) in May 2013. A complex, multidisciplinary administrative and engineering intervention centred on the TWH water distribution system (WDS) was executed to terminate the outbreak and minimise recurrence risk. LPSG1 isolates were collected prospectively from the TWH WDS in addition to retrospective and prospective patient isolates for Whole Genome Sequencing (WGS).
Methods: A rapid disinfection of the hospital WDS with cycles of alkaline detergent, super-chlorination and then residual chlorination; combined with plumbing remediation and in-line filtration was instituted. LPSG1 was cultured from patient sputum (n = 4), endobronchial washings (n = 3), pleural fluid (n = 1) and the Wesley Hospital WDS (n = 39). WGS allowed comparison with the L. pneumophila Paris reference strain to infer phylogenetic and epidemiological relationships.
Results: Isolates from 2011, the 2013 outbreak, and from a case in 2015 were closely related to all 2013 hospital water isolates based on single nucleotide polymorphisms and mobile genetic element profiles, suggesting a single L. pneumophila population as the source of nosocomial infection. The LPSG1 population evolved to comprise three clonal variants, each associated with different parts of the hospital WDS. A water quality risk management plan is in place with WDS biofilm management, disinfection and other risk mitigation strategies in a “maintenance phase” with verification monitoring.
Conclusions: This study is an example of the use of clinical and genomic epidemiological methods together with a major engineering intervention to remove WDS biofilm to characterise and eliminate a LPSG1 population responsible for nosocomial infections.