Two Distinct Outbreaks of Extended-spectrum Beta-lactamase-producing Klebsiella Species in a Neonatal and Pediatric Intensive Care Unit in Switzerland.

BACKGROUND: Healthcare-associated infections caused by Klebsiella spp. are associated with substantial morbidity and mortality in neonatal and pediatric intensive care units. We describe 2 outbreaks of extended-spectrum beta-lactamase-producing Klebsiella michiganensis and Klebsiella pneumoniae in the same unit. METHODS: Weekly screening for extended-spectrum beta-lactamase-producing Enterobacterales and environmental sampling were performed during outbreaks. Isolates were analyzed using whole genome sequencing (WGS; Illumina) and core genome multilocus sequence typing. Selected isolates underwent long-read sequencing (Oxford Nanopore Technology) to assess plasmid transmission. Risk factors for colonization in patients up to 1 month of age were evaluated using univariable and multivariable logistic regression. RESULTS: During the first outbreak, K. michiganensis was detected in 16.7% (19/114) of screened patients and in 5 environmental samples. During the second outbreak, K. pneumoniae was identified in 14.4% (17/118) of patients and in 3 environmental samples. WGS demonstrated clonal clustering of the K. michiganensis isolates, belonging to ST-231, carrying blaCTX-M-9 and of the K. pneumoniae belonging to ST-469, carrying blaCTX-M-15. Hybrid genome assembly showed that blaCTX-M-carrying plasmids were unrelated, excluding plasmid-mediated transmission. In multivariable analysis, higher gestational age at birth was associated with lower odds of colonization, adjusted for antibiotic exposure, central venous catheter use, ventilation and pediatric index of mortality 2 score. Infection control interventions included reinforcement of standard precautions, sink disinfection and removal of a contaminated sink. CONCLUSIONS: WGS elucidated outbreak transmission dynamics, identified environmental reservoirs, and excluded plasmid transmission, thereby informing targeted infection control measures. Low gestational age at birth was identified as a risk factor for colonization.