Clinical and molecular characteristics of OXA-72-producing Acinetobacter baumannii ST636 outbreak at a neonatal intensive care unit in Serbia

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To describe an Acinetobacter baumannii outbreak among preterm neonates in a neonatal intensive care unit (NICU) in Serbia. A case-control study was conducted in the NICU at the Institute of Neonatology, Belgrade, Serbia. The case definition of A.baumannii bloodstream infection (BSI) was blood culture confirmation of systemic infection. Isolation, identification and susceptibility testing were performed using conventional methods. Molecular characterization of isolates included resistance gene detection, pulsed-field gel electrophoresis (PFGE) and multi-locus sequence typing. Outcomes and clinical and demographic data were obtained from patients' medical records. An infection prevention team was formed and infection control interventions were implemented. During the outbreak period (May-July 2018), there were 13 cases of A.baumannii BSI among 82 hospitalized neonates. All A.baumannii strains were carbapenem resistant and susceptible to colistin. Molecular characterization of the isolates revealed that they harboured blaOXA66 and blaOXA72 beta-lactamases and belonged to sequence type 636, while the PFGE pattern indicated clonal spread. Lower gestational age, lower Apgar score, vaginal delivery and mechanical ventilation were risk factors for A.baumannii infection. Four patients died, eight patients were treated successfully with colistin, and one patient with sepsis and meningitis on dual ampicillin-sulbactam and colistin therapy recovered with sequelae. The outbreak was eventually controlled by reinforcement of the infection control measures based on a multi-tiered interventional approach. This is the first description of an outbreak of BSI among preterm neonates caused by A.baumannii blaOXA66/blaOXA72/ST636 in Serbia.