A case-control study to identify predictors of 14-day mortality following carbapenem-resistant Acinetobacter baumannii bacteraemia

Carbapenem-resistant Acinetobacter baumannii (CRAB) is an increasingly common nosocomial pathogen. We sought to identify clinical and microbiological predictors of 14-day mortality among patients with CRAB bacteraemia. This case-control study included all adult patients in one Israeli hospital with CRAB on blood culture between July 2008 and June 2011. Cases were defined as patients who died within 14days of bacteraemia onset and controls as patients who survived over 14days. Sequence-typing of the bla(OXA-51-like) gene and REP-PCR identified CRAB clone groups. Logistic regression was performed to analyze predictors of 14-day all-cause mortality. To correct for differences in treatment onset, Cox regression was used to examine the effect of receiving an active antibiotic. Eighty-three cases and 89 controls were included. Six major CRAB clone groups were identified, with 14-day mortality ranging from 17 to 66%. Independent predictors of 14-day mortality were severity of illness (OR=1.38 for each 1-point increase in Sequential Organ Failure Assessment (SOFA) score; 95% CI, 1.21, 1.56), independence in activities of daily living (ADL) on admission (OR=3.40; 95% CI, 1.20, 9.67, for fully dependent vs. independent), surgery before bacteraemia (OR=0.25; 95% CI, 0.11, 0.59) and clone group (OR=7.76; 95% CI, 2.52, 23.85, for the most virulent group vs. the reference group). In the multivariate Cox model using a propensity score to adjust for SOFA, clone, ADL and surgery, active antibiotic treatment was protective (HR=0.30; 95% CI, 0.15, 0.60). Differences in virulence between CRAB clones may partly explain heterogeneous results in previous studies of mortality following CRAB infection.