Objective: To investigate for the factors associated with acquisition of imipenem-resistant Acinetobacter baumannii (IRAB) at Songklanagarind Hospital and the subsequent patient mortality outcome.
Design: A case-control study was conducted to evaluate the risk factors for IRAB acquisition using imipenemsensitive A. baumannii (ISAB) as controls. A retrospective cohort study was employed to assess the factors associated with mortality in the hospital.
Setting: An 850-bed university hospital served as a medical school, training hospital, tertiary care, and referral center for the southern part of Thailand.
Patients: The patients who acquired A. baumannii during their stay in the hospital.
Results: Between July 2003 and September 2005, there were 2,130 isolates of A. baumannii from clinical specimens of 1,237 hospitalized patients. The medical records of 899 admissions to the hospital were available for review. The significant risk factors associated with IRAB acquisition, identified from a case-control study and multiple logistic regression analysis included previous admission to medical-surgical intensive care unit (ICU), respiratory care unit (RCU), previous use of multiple classes of antibiotics, and previous use of imipenem. The cohort study revealed that the mortality rate in the patients with IRAB compared to ISAB were 33.8% and 24.1% respectively, yielding an unadjusted odds ratio of 1.6 (95% CI = 1.2-2.2). However, after controlling for confounding factors by multivariate analysis IRAB did not show the increased mortality.
Conclusion: The outbreak of IRAB at Songklanagarind Hospital is associated with increasing antibiotic pressure particularly imipenem and the admission to the ICU and RCU. The excess patient mortality rate attributable to IRAB is not significantly different from that attributable to ISAB.

Keywords: Epidemic, Outbreak, Acinetobacter baumannii, Antimicrobial-resistant, Imipenem