A hospital-wide outbreak of ESBL-producing Klebsiella oxytoca associated with contaminated sinks and associated plumbing: outbreak report, risk factor analysis and plasmid mapping.

Objectives: To describe a sink-related outbreak of Klebsiella oxytoca and determine risk factors for acquiring the outbreak strain.

Methods: Case-control analysis, environmental sampling from sinks, short-read whole genome sequencing and long-read whole genome sequencing of selected isolates.

Results: Whole genome sequencing revealed genetic clustering of 47 patient cases over 26 months. The outbreak strain (Klebsiella oxytoca, sequence type 2, with or without blaCTX-M containing plasmid) was also identified in sinks or adjacent plumbing in four rooms in two wards. After adjustment for age, sex, and length of stay, four significant risk factors for infection or colonization of the outbreak strain were found: age (OR per additional year: 1.03 (95% CI: 1.00-1.07); length of stay (OR per additional day: 1.04 (95% CI: 1.02-1.08); urinary catheter (OR: 7.65 (95% CI: 2.10-27.8; OR per additional day: 1.06 (95% CI: 1.01-1.12); and diarrhoea (OR: 3.10 (1.03-9.35). Long-read plasmid sequencing revealed strong indications of plasmid transmission from the outbreak strain to other sequence types of Klebsiella oxytoca. Multifaceted interventions were employed, including exchange of sinks strainers, traps, and piping, behavioural interventions, and reinforced cleaning and disinfection. Outbreak control has so far not been achieved despite interventions.

Conclusions: Klebsiella oxytoca established in sink plumbing biofilm was associated with a prolonged outbreak difficult to control. Age, length of stay, urinary catheter and diarrhoea were risk factors for acquiring the outbreak strain. Both clonal and horizontal transmission occurred.