First outbreak of extended-spectrum β-lactamase-producing Klebsiella pneumoniae in a Norwegian neonatal intensive care unit; associated with contaminated breast milk and resolved by strict cohorting.

Neonatal intensive care units (NICUs) are vulnerable to nosocomial outbreaks caused by multiresistant Enterobacteriaceae, but no reports of NICU outbreaks of extended-spectrum β-lactamase (ESBL) producing Klebsiella pneumoniae have previously been published from countries with a low level of antimicrobial resistance such as the Scandinavian countries. We describe a clonal outbreak of CTX-M-15 -producing Klebsiella pneumoniae affecting 58 infants in the neonatal intensive care unit at Stavanger University Hospital, Norway, during a period of 4 months, 2008-2009. The clone spread widely and rapidly in the NICU, and extensive interventions were required to terminate the outbreak. In contrast to previous outbreaks, only one infant acquired a systemic infection caused by the outbreak strain, probably due to a favourable epidemic strain lacking the most common virulence factors. A probable index case was identified, due to multiple positive breast milk samples collected from the infant's mother before and after the infant's transfer from another hospital. Breast milk samples from 3/18 (17%) mothers of colonized infants were positive for ESBL-producing K. pneumoniae. Vertical transmission of ESBL-producing bacteria has been shown previously,’but the possibility of transmission of ESBL-producing K. pneumoniae through expressed breast milk is reported here for the first time. The increasing occurrence of ESBL-producing’Enterobacteriaceae should therefore encourage changes in diagnostic routines for bacterial screening of breast milk.