Outbreak of extended-spectrum β-lactamase-producing Escherichia coli transmitted through breast milk sharing in a neonatal intensive care unit

Routine surveillance in a neonatal intensive care unit (NICU) showed an increased detection of extended-spectrum β-lactamase (ESBL)-producing Escherichia coli (ESBL-E. coli) in August 2012, following nearly a year without detection.To describe the investigation and interventions by a hospital infection control team of an outbreak of ESBL-E. coli in a NICU.Six neonates with positive cultures of ESBL-E. coli (five with respiratory colonization, one with a urinary tract infection), control infants who were negative for ESBL-E. coli during the study period, and mothers who donated their breast milk were included. A case-control study was performed to identify possible risk factors for positive ESBL-E. coli cultures and molecular typing of isolated strains by pulsed-field gel electrophoresis.The odds ratio for ESBL-E. coli infection after receiving shared unpasteurized breast milk during the study period was 49.17 (95% confidence interval: 6.02-354.68; P0.05). The pulsed-field gel electrophoresis pattern showed that all strains were identical, and the same pathogen was detected in freshly expressed milk of a particular donor. After ceasing the breast milk sharing, the outbreak was successfully terminated.This outbreak indicates that contamination of milk packs can result in transmission of a drug-resistant pathogen to newborn infants. Providers of human breast milk need to be aware of the necessity for low-temperature pasteurization and bacterial cultures, which should be conducted before and after freezing, before prescribing to infants.