Clonal spread and patient risk factors for acquisition of extensively drug-resistant Acinetobacter baumannii in a neonatal intensive care unit in Italy

Abstract

To report an outbreak of extensively drug-resistant (XDR) Acinetobacter baumannii in the neonatal intensive care unit (NICU) of an Italian university hospital. Patient risk profiles for acquisition of A.baumannii and measures used to control the outbreak are described. Antibiotic susceptibility of strains was evaluated by microdilution. Genotyping was performed by pulsed-field gel electrophoresis (PFGE) and multi-locus sequence typing. Carbapenemase genes were analysed by polymerase chain reaction and DNA sequencing. A case-control study was designed to identify risk factors for acquisition of A.baumannii. A.baumannii was isolated from 22 neonates, six of whom were infected. One major PFGE type was identified, assigned to sequence type (ST) 2, corresponding to International Clone II; this was indistinguishable from isolates from the adult ICU in the same hospital. A.baumannii isolates were resistant to aminoglycosides, quinolones and classes of β-lactam antibiotics, but were susceptible to tigecycline and colistin. Carbapenem resistance was associated with the presence of transposon Tn2006 carrying the bla(OxA-23) gene. Length of NICU stay, length of exposure to A.baumannii, gestational age, use of invasive devices and length of exposure to invasive devices were significantly associated with acquisition of A.baumannii on univariate analysis, while length of exposure to central venous catheters and assisted ventilation were the only independent risk factors after multi-variate analysis. This XDR A.baumannii outbreak in an NICU was probably caused by intrahospital transfer of bacteria via a colonized neonate whose mother was admitted to the adult ICU. Strengthened infection control measures were necessary to control the outbreak.