Increasing Occurrence of Multidrug-Resistance in Acinetobacter baumannii Isolates From Four German University Hospitals, 2002-2006

Background: Acinetobacter baumannii can cause severe infections, mainly in critically ill inpatients. Treatment is complicated by multidrug-resistance (MDR). In Germany, to date, little is known on the extent of MDR in A. baumannii isolated from inpatients in German hospitals and potential factors influencing the emergence of MDR. Materials and Methods: We retrospectively analysed the data of A. baumannii isolates from the inpatients of four German university hospitals, tested for antimicrobial resistance with the broth dilution method between 2002 and 2006. We defined MDR as resistance to three or more classes of recommended drugs. After calculating the proportions of MDR in A. baumannii isolates, we investigated the association between MDR in A. baumannii and year of pathogen isolation, hospital, ward type, specimen and demographics. We performed descriptive analysis and multivariable logistic regression. Additionally, proportions of in vitro drug effectiveness against multidrug-resistant and non-multidrug-resistant A. baumannii isolates were determined. Results: MDR was found in 66 of 1,190 (5.6%) A. baumannii isolates and increased from 2.1% in 2002 to 7.9% in 2006. The highest proportions of MDR were found in hospital A (8.9%), in intensive care units (7.3%), in isolates from blood (7.6%) and in mate patients aged 60 years or older (6.6%). In multivariable analysis, the chance of MDR in A. baumannii isolates increased with the successive years of pathogen isolation (odds ratio [OR] 1.3, 95% confidence interval [CI] 1.1-1.5) and there was a higher risk of MDR in A. baumannii in intensive care units (OR 1.8, 95% CI 1.1-2.9). The lowest in vitro antibiotic resistance was found in meropenem, imipenem and ampicillin/sulbactam, with 33, 37 and 39% for multidrug-resistant and 0.4, 1 and 3% in non-multidrug-resistant A. baumannii isolates, respectively. Conclusions: The increase of MDR in A. baumannii isolates from 2002 to 2006 in four hospitals suggests that clinicians in Germany may expect a rising proportion of MDR in A. baumannii isolates among inpatients. The antimicrobial susceptibility testing of A. baumannii isolates against recommended drugs, combined with in-house antimicrobial resistance surveillance, is needed to ensure appropriate treatment.