Antimicrobial treatment and clinical outcome for infections with carbapenem- and multiply-resistant Acinetobacter baumannii around London

Carbapenem- and multiply-resistant Acinetobacter baumannii (C-MRAB) are challenging pathogens, often susceptible only to polymyxins and tigecycline. We reviewed clinical outcomes in relation to antibiotic treatment for 166 consecutive patients infected or colonised with these organisms at 18 hospitals around London, UK. Clinical data were obtained along with the isolates, which were typed by pulsed-field gel electrophoresis (PFGE). Outcomes were compared for colonised and infected patients and in relation to treatment, with associations examined by logistic regression. Most subjects (103/166; 62%) were in Intensive Care Units (ICUs) or high dependency units; 84 (50.6%) were judged to be infected and 73 (44.0%) were colonised, with 9 indeterminate. Among the 166 C-MRAB isolates, 141 belonged to OXA-23 clone 1, a European clone II lineage. Survival rates among infected and colonised patients were 68% and 67%, respectively (P > 0.05), indicating little attributable mortality. Univariate and multivariate analyses indicated poorer outcomes among ICU-infected patients and those with pulmonary infection or bacteraemia, whereas trauma patients had significantly better outcomes than the generality. Outcomes varied with hospital, even in multivariate analysis, reflecting either differences in management or case mix. There was little association between outcome and therapy with colistin and/or tigecycline except that, among patients with respiratory infection, 12/15 treated with intravenous colistin alone had poor outcome compared with 1/8 whose therapy include nebulised colistin. This difference was significant (P = 0.003), although the patients receiving nebulised drug were mostly younger, included trauma cases and were at a hospital with good outcomes.