Overestimation of an outbreak of Enterobacter cloacae in a neonatal intensive care unit in Germany, 2015.

BACKGROUND: In August 2015 seventeen neonates with Enterobacter (E.) cloacae colonisation were identified in a neonatal intensive care unit (NICU) in Germany. Two developed severe brain abscesses. Despite temporary NICU closure in September another infant with E. cloacae colonisation was detected in October 2015.

METHODS: We defined potential cases as inpatients treated in the NICU or any paediatric/maternity ward in 2015 with E. cloacae in any specimen before molecular typing. Cases were at first confirmed by arbitrarily-primed-polymerase-chain-reaction (AP-PCR) and later by XbaI-macrorestriction/pulsed-field gel electrophoresis (PFGE) and next-generation-sequencing (NGS). Enhanced barrier precautions and cohorting were implemented for all potential cases and microbiological screening was extended from NICU to all paediatric/maternity wards.

RESULTS: Of forty-one potential cases (occurring between 08/04/2015 and 15/11/2015 in four wards) the isolates of twenty-three shared identical AP-PCR patterns; three without plausible epidemiological link. PFGE analyses verified only ten cases (all in the NICU); NGS analysis confirmed these results. In addition six cases without isolates available for genotyping were closely linked in place and time.

CONCLUSIONS: Forty-one suspected patients were cohorted and the NICU was temporarily closed. Further analyses revealed that only sixteen cases belonged to the outbreak. Only close interdisciplinary collaboration and highly discriminatory genotyping methods allowed to clearly differentiate between cases and non-cases in this E. cloacae outbreak.