First outbreak of extended‐spectrum β‐lactamase‐producing K lebsiella pneumoniae in a N orwegian neonatal intensive care unit; associated with contaminated breast milk and resolved by strict cohorting

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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.