Unusual genetic heterogeneity of Acinetobacter baumannii isolates in a university hospital in Italy

Background: Acinetobacter baumannii has become an increasingly important no socomial pathogen, particularly in intensive care units (ICUs). The aim of this investigation was to study the molecular epidemiology of A baumanii in a university hospital in Italy. Methods: All A baumanii isolates were collected and typed with phenotypic a nd genotypic methods during a 7-month period. A 1-year prospective surveill ance of ICU-acquired infections was performed by using the National Nosocom ial Infections Surveillance methodology. Results: A baumanni accounted for 28.4% of all infections and 46.7% of all pneumonia acquired in the ICU, with a nosocomial infection rate of 12.4% or 8 infections per 1000 patient-days. Risk factors for A baumannii acquisiti on in the ICU were mechanical ventilation and previous use of broad-spectru m antibiotics, whereas administration of carbapenems showed a significant p rotective effect. Pulsed-field gel electrophoresis of genomic ApaI digests identified at least 5 outbreaks in the ICU caused by 5 different clones, on e replacing the other in a well-defined temporal order. Conclusions: Whereas the sequential temporal cluster of epidemic clones in the ICU is intriguing and requires further research, the clear evidence of cross-contamination of A baumannii isolates involved with infections in the ICU demands extensive preventive efforts.