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Epidemiology and Impact of Imipenem Resistance in Acinetobacter baumannii

  • Ebbing Lautenbach (a1) (a2) (a3) (a4), Marie Synnestvedt (a5) (a4), Mark G. Weiner (a5) (a4), Warren B. Bilker (a2) (a3) (a4), Lien Vo (a6), Jeff Schein (a6) and Myoung Kim (a6)...

Acinetobacter baumannii is an emerging gram-negative pathogen that can cause healthcare-acquired infections among patients. Treatment is complicated for cases of healthcare-acquired infection with A. baumannii resistant to imipenem.


To elucidate the risk factors for imipenem-resistant A. baumannii (IRAB) infection or colonization and to identify the effect of resistance on clinical and economic outcomes.


We analyzed data from 2 medical centers of the University of Pennsylvania. Longitudinal trends in the prevalence of IRAB clinical isolates were characterized during the period from 1989 through 2004. For A. baumannii isolates obtained from 2001 through 2006, a case-control study was conducted to investigate the association between prior carbapenem use and IRAB infection or colonization, and a cohort study was performed to identify the effect of IRAB infection or colonization on mortality, length of stay after culture, and hospital cost after culture.


From 1989 through 2004, the annual prevalence of IRAB isolates ranged from 0% to 21%. During the period from 2001 through 2006, there were 386 unique patients with A. baumannii isolates, and 89 (23.1%) had IRAB isolates. Prior carbapenem use was independently associated with IRAB infection or colonization (adjusted odds ratio, 3.04 [95% confidence interval, 1.07–8.65]). There was a borderline significant association between IRAB infection or colonization and mortality, although this association was limited to isolates recovered from blood samples (adjusted odds ratio, 5.30 [95% confidence interval, 0.81–34.59]). Compared with patients with imipenem-susceptible A. baumannii infection or colonization, patients with IRAB infection or colonization had a longer hospital stay after culture (median, 21 vs 16 days; P = .07) and greater hospital charges after culture (mean, $334,516 vs $276,059; P = .03). After controlling for patient location in an intensive care unit, transfer from another facility, and length of hospital stay before culture, there was no longer an independent association between IRAB infection or colonization and higher cost after culture and length of stay after positive culture result.


Many A. baumannii isolates exhibit imipenem resistance, which is strongly associated with prior use of carbapenems. Given the high mortality rate associated with A. baumannii infection or colonization, interventions to curb further emergence of cases of IRAB infection and strategies to optimize therapy are needed.

Corresponding author
Center for Clinical Epidemiology and Biostatistics, University of Pennsylvania School of Medicine, 825 Blockley Hall, 423 Guardian Drive, Philadelphia, PA 19104-6021 (
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1.Falagas, ME, Kopterides, P, Siempos, II. Attributable mortality of Acine-tobacter baumannii infection among critically ill patients. Clin Infect Dis 2006;43:389.
2.Fournier, PE, Richet, H. The epidemiology and control of Acinetobacter baumannii in health care facilities. Clin Infect Dis 2006;42:692699.
3.Ibrahim, EH, Sherman, G, Ward, S, Fraser, VI, Kollef, MH. The influence of inadequate antimicrobial treatment of bloodstream infections on patient outcomes in the ICU setting. Chest 2000;118:146155.
4.Kollef, MH. The importance of appropriate initial antibiotic therapy for hospital-acquired infections. Am I Med 2003;115:582584.
5.Paterson, DL. The epidemiological profile of infections with multidrug-resistant Pseudomonas aeruginosa and Acinetobacter species. Clin Infect Dis 2006;43(Suppl 2):S43S48.
6.Gales, AC, Jones, RN, Sader, HS. Global assessment of the antimicrobial activity of polymyxin B against 54 731 clinical isolates of gram-negative bacilli: report from the SENTRY antimicrobial surveillance programme (2001-2004). Clin Microbiol Infect 2006;12:315321.
7.McGowan, JE. Resistance in nonfermenting gram-negative bacteria: multidrug resistance to the maximum. Am J Med 2006;119(Suppl 1):S29S36.
8.Harris, AD, Karchmer, TB, Carmeli, Y, Samore, MH. Methodological principles of case-control studies that analyzed risk factors for antibiotic resistance: a systematic review. Clin Infect Dis 2001;32:10551061.
9.Gasink, LB, Fishman, NO, Weiner, MG, Nachamkin, I, Bilker, WB, Lautenbach, E. Fluoroquinolone-resistant Pseudomonas aeruginosa: assessment of risk factors and clinical impact. Am J Med 2006;199:e19e25. Available at: Accessed October 15, 2009.
10.Lautenbach, E, Weiner, MG, Nachamkin, I, Bilker, WB, Sheridan, A, Fishman, NO. Imipenem resistance among Pseudomonas aeruginosa isolates: risk factors for infection and impact of resistance on clinical and economic outcomes. Infect Control Hosp Epidemiol 2006;27:893900.
11. Clinical and Laboratory Standards Institute. Performance standards for antimicrobial susceptibility testing: 18th informational supplement. CLSI document. Wayne, PA: CLSI, 2008:M100-S18.
12.Defez, C, Fabbro-Peray, P, Bouziges, N, et al.Risk factors for multidrug-resistant Pseudomonas aeruginosa nosocomial infection. J Hosp Infect 2004;57:209216.
13.Falagas, ME, Koletsi, PK, Bliziotis, IA. The diversity of definitions of multidrug-resistant (MDR) and pandrug-resistant (PDR) Acinetobacter baumannii and Pseudomonas aeruginosa. J Med Microbiol 2006;55:16191629.
14.MacAdam, H, Zaoutis, TE, Gasink, LB, Bilker, WB, Lautenbach, E. Investigating the association between antibiotic use and antibiotic resistance: impact of different methods of categorizing prior antibiotic use. Int J Antimicrob Agents 2006;28:325332.
15.Gasink, LB, Zaoutis, TE, Bilker, WB, Lautenbach, E. The categorization of prior antibiotic use: impact on the identification of risk factors for drug resistance in case control studies. Am J Infect Control 2007;35:638642.
16.Armitage, P. Test for linear trend in proportions and frequencies. Biometrics 1955;11:375386.
17.Kleinbaum, DG, Kupper, LL, Morgenstern, H. Epidemiologie Research: Principles and Quantitative Methods. New York, New York: Van Nostrand Reinhold; 1982.
18.Mantel, N, Haenszel, W. Statistical aspects of the analysis of data from retrospective studies of disease. J Natl Cancer Inst 1959;22:719748.
19.Hosmer, DO, Lemeshow, SL. Applied Logistic Regression. New York, New York: Wiley and Sons; 1989.
20.Sun, GW, Shook, TL, Kay, GL. Inappropriate use of bivariable analysis to screen risk factors for use in multivariable analysis. J Clin Epidemiol 1996;49:907916.
21.Mickey, RM, Greenland, S. The impact of confounder selection criteria on effect estimation. Am J Epidemiol 1989;129:125137.
22.Garner, JS, Jarvis, WR, Emori, TG, Horau, TC, Hughes, JM. CDC definitions for nosocomial infections, 1988. Am J Infect Control 1988;16:128140.
23.Lee, SO, Kim, NJ, Choi, SH, et al.Risk factors for acquisition of imipenem-resistant Acinetobacter baumannii: a case-control study. Antimicrob Agents Chemother 2004;48:224228.
24.del Mar Tomas, M, Cartelle, M, Pertega, S, et al.Hospital outbreak caused by a carbapenem-resistant strain of Acinetobacter baumannii: patient prognosis and risk-factors for colonisation and infection. Clin Microbiol Infect 2005;11:540546.
25.Falagas, ME, Kopterides, P. Risk factors for the isolation of multi-drug-resistant Acinetobacter baumannii and Pseudomonas aeruginosa: a systematic review of the literature. J Hosp Infect 2006;64:715.
26.Husni, RN, Goldstein, LS, Arroliga, AC, et al.Risk factors for an outbreak of multi-drug-resistant Acinetobacter nosocomial pneumonia among intubated patients. Chest 1999;115:13781382.
27.Carbonne, A, Naas, T, Blanckaert, K, et al.Investigation of a nosocomial outbreak of extended-spectrum β-lactamase VEB-1-producing isolates of Acinetobacter baumannii in a hospital setting. J Hosp Infect 2005;60:1418.
28.Smith, PW, Bennett, G, Bradley, S, et al.SHEA/APIC guideline: infection prevention and control in the long-term care facility, July 2008. Infect Control Hosp Epidemiol 2008;29:785814.
29.Lautenbach, E, Fishman, NO, Bilker, WB, et al.Risk factors for fluoroquinolone resistance in nosocomial Escherichia coli and Klebsiella pneumoniae infections. Arch Intern Med 2002;162:24692477.
30.Lautenbach, E, Strom, BL, Bilker, WB, Patel, JB, Edelstein, PH, Fishman, NO. Epidemiological investigation of fluoroquinolone resistance in infections due to extended-spectrum β-lactamase-producing Escherichia coli and Klebsiella pneumoniae. Clin Infect Dis 2001;33:12881294.
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Infection Control & Hospital Epidemiology
  • ISSN: 0899-823X
  • EISSN: 1559-6834
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