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Acinetobacter baumannii Infections Among Patients at Military Medical Facilities Treating Injured U.S. Service Members, 2002--2004
Acinetobacter baumannii is a well known but relatively uncommon cause of health-care--associated infections. Because the organism has developed substantial antimicrobial resistance, treatment of infections attributed to A. baumannii has become increasingly difficult (1). This report describes an increasing number of A. baumannii bloodstream infections in patients at military medical facilities in which service members injured in the Iraq/Kuwait region during Operation Iraqi Freedom (OIF) and in Afghanistan during Operation Enduring Freedom (OEF) were treated. The number of these infections and their resistance to multiple antimicrobial agents underscore 1) the importance of infection control during treatment in combat and health-care settings and 2) the need to develop new antimicrobial drugs to treat these infections.
During January 1, 2002--August 31, 2004, military health officials identified 102 patients with blood cultures that grew A. baumannii at military medical facilities treating service members injured in Afghanistan and the Iraq/Kuwait region. All of these cases met the criteria for A. baumannii bloodstream infection on the basis of criteria established by CDC's National Nosocomial Infection Surveillance (NNIS) system (2). Of these 102 cases, 85 (83%) were associated with activities during OIF and OEF. Most of the infections were reported from Landstuhl Regional Medical Center (LRMC), Germany (33 patients: 32 OIF/OEF casualties, one non-OIF/OEF), and Walter Reed Army Medical Center (WRAMC), District of Columbia (45 patients: 29 OIF/OEF casualties, 16 non-OIF/OEF). In both facilities, the number of patients with A. baumannii bloodstream infections in 2003 and 2004 exceeded those reported in previous years (one case during 2000--2002 at LRMC; two cases during 2001--2002 at WRAMC).
Of the 33 patients with A. baumannii bloodstream infections at LRMC, 32 (97%) were men; the median age was 30 years (range: 19--72 years). Thirty (91%) patients sustained traumatic injuries in either the Iraq/Kuwait region (25) or in Afghanistan (five). The majority (67%) were active-duty members of the U.S. Armed Forces. Thirty-two (97%) were transferred directly to the LRMC intensive care unit (ICU) from a combat theater military medical facility. In 22 (67%) of these patients, bloodstream infections were detected from blood cultures obtained within 48 hours of ICU admission.
Of the 45 patients with A. baumannii bloodstream infections at WRAMC, 39 (87%) were males; the median age was 39 years (range: 6--86 years). Twenty-nine (64%) patients sustained traumatic injuries in the Iraq/Kuwait region. Of these, 18 (62%) had bloodstream infections detected from blood cultures obtained within 48 hours of hospital admission after transfer from a combat theater medical or other military medical facility.
Antimicrobial susceptibility testing (AST) was performed by using microdilution. Results of 33 A. baumannii isolates from LRMC and 45 isolates from WRAMC indicated widespread resistance to antimicrobial agents commonly used to treat infections with this organism. AST results, expressed as a percentage of susceptible isolates, were as follows: imipenem (LRMC: 87%; WRAMC: 82%), amikacin (LRMC: 80%; WRAMC: 48%), ampicillin/sulbactam (LRMC: 8%; WRAMC: 35%), piperacillin/tazobactam (LRMC: 0%; WRAMC: 27%), cefepime (LRMC: 0%; WRAMC: 22%), and ciprofloxacin (LRMC: 3%; WRAMC: 20%).
Among the WRAMC isolates, 13 (35%) were susceptible to imipenem only, and two (4%) were resistant to all drugs tested. One antimicrobial agent, colistin (polymyxin E), has been used to treat infections with multidrug-resistant A. baumannii; however, AST for colistin was not performed on isolates described in this report.
In addition to LRMC and WRAMC, three other military treatment facilities have identified A. baumannii bloodstream infections in service members injured in Iraq, Kuwait, and Afghanistan: U.S. Navy hospital ship (USNS) Comfort (11 patients), National Naval Medical Center (NNMC), Bethesda, Maryland (eight), and Brooke Army Medical Center (BAMC), San Antonio, Texas (five).
Reported by: PT Scott, MD, Army Medical Surveillance Activity, District of Columbia. K Petersen, DO, National Naval Medical Center, Bethesda, Maryland. J Fishbain, MD, DW Craft, PhD, AJ Ewell, PhD, K Moran, MD, DC Hack, MD, Walter Reed Army Medical Center, District of Columbia. GA Deye, MD, S Riddell, PhD, G Christopher, MD, Landstuhl Regional Medical Center, Landstuhl, Germany. JD Mancuso, MD, BP Petruccelli, MD, US Army Center for Health Promotion and Preventive Medicine. T Endy, MD, L Lindler, PhD, Walter Reed Army Institute of Research, Silver Spring, Maryland. K Davis, MD, Brooke Army Medical Center, San Antonio, Texas. EG Milstrey, PhD, US Army 30th Medical Brigade. L Brosch, MD, Uniformed Svcs Univ of the Health Sciences, Bethesda, Maryland. J Pool, MS, Office of the Surgeon General of the Army. CL Blankenship, MD, Office of the Surgeon General of the Navy. CJ Witt, DVM, JL Malone, MD, Global Emerging Infections Surveillance and Response System; DN Tornberg, MD, Office of Health Affairs, US Dept of Defense. A Srinivasan, MD, Div of Healthcare Quality Promotion, National Center for Infectious Diseases, CDC.
A. baumannii are a species of gram-negative bacteria commonly found in water and soil. During 1963--2003, A. baumannii became an increasingly important cause of nosocomial infections, particularly in ICUs (3). Treatment of infections attributed to A. baumannii can be difficult because the organism has intrinsic resistance to certain antimicrobial agents and has acquired resistance to many others (3). In health-care settings, colonized and infected patients are often the sources of A. baumannii infections; however, the ability of the organism to survive for prolonged periods on environmental surfaces also has contributed to protracted outbreaks in these settings (1).
In a recent national survey of hospital laboratories, A. baumannii infections accounted for only 1.3% of health-care--associated bloodstream infections (4). However, the findings in this report indicate an increase in the number of reported A. baumannii bloodstream infections in patients at military medical facilities in which service members injured in Iraq, Kuwait, and Afghanistan are treated.
The sources of the A. baumannii that led to the infections described in this report are under investigation. During the Vietnam War, A. baumannii was reported to be the most common gram-negative bacillus recovered from traumatic injuries to extremities, and more recent reports have identified A. baumannii infections in patients who suffered traumatic injuries, suggesting environmental contamination of wounds as a potential source (5--8). Although some of the patients identified in this report had evidence of bloodstream infections at the time of admission to military medical facilities, whether the infections were acquired from environmental sources in the field or during treatment at (or evacuation from) other military medical facilities (e.g., field hospitals) is unknown. Information on patients described in this report is being reviewed to examine potential risk factors for A. baumannii bloodstream infection. In addition to exploring traditionally reported risk factors such as antimicrobial exposure, ICU admission, vascular access, and mechanical ventilation, this investigation will involve detailed reviews of geographic locations where injuries occurred and reviews of the movement of injured patients through treatment facilities. An environmental microbiology survey of both indigenous soil samples and treatment facilities is also under way to explore the potential contribution of environmental contamination to this outbreak. Molecular analysis with pulsed-field gel electrophoresis of patient and environmental isolates will be performed to further characterize the potential contribution of environmental contamination.
The bacterial isolates described in this report demonstrated antimicrobial-resistance patterns similar to multidrug-resistant A. baumannii from ICUs in the United States and Europe (3,4). Data from the NNIS system also indicate that resistance among Acinetobacter isolates is increasing (CDC, unpublished data, 2004). The high level of antimicrobial resistance is a challenge to clinicians treating A. baumannii infections. In some cases, the only effective antimicrobial agent is colistin (polymyxin E); however, this agent is seldom used because of its high toxicity (9). Use of colistin, possibly in combination with other agents, might be effective; however, new agents active against multidrug-resistant A. baumannii are needed. Treatment of patients infected with A. baumannii is being monitored to determine factors predictive of success and failure, to better understand the impact of antimicrobial resistance on therapy, and to monitor the potential toxicities of treatment regimens that include colistin.
Identification of colonized and infected patients, combined with implementation of infection-control measures such as hand-hygiene and contact-isolation precautions, might help prevent transmission of this organism within medical facilities (1). Interventions recommended by military medical officials have included 1) institution of active surveillance of groin, axillary, and/or wound cultures for A. baumannii for all patients; 2) use of contact precautions for colonized or infected patients; and 3) increased availability and use of alcohol-based hand rubs. Laboratory surveillance for A. baumannii has been initiated at LRMC, NNMC, WRAMC, and BAMC, and, as much as possible, at each forward-deployed combat support hospital and medical treatment facility in Iraq, Kuwait, and Afghanistan.
Clinicians who treat patients who have recently been hospitalized (especially in ICUs) at the military hospitals described in this report should be aware of the potential for colonization and infection with A. baumannii. Additional information on A. baumannii is available at http://www.cdc.gov/ncidod/hip. Clinical management and wound-care guidelines have been developed to help prevent and mitigate A. baumannii infections in military treatment facilities (10). Clinicians with specific questions about A. baumannii among U.S. service members should contact the U.S. Army Center for Health Promotion and Preventive Medicine, telephone 800-222-9698.
This report is based, in part, on contributions by E Gourdine, MS, 31st Combat Support Hospital; A O'Brien, MPH, MultiNational Corps, Baghdad, Iraq. W Wortman, Kadix Systems, Aberdeen Proving Ground, Maryland. M Pe, K Snow, MS, EA Hulten, MD, M Buddle, AF Shorr, MD, Walter Reed Army Medical Center, District of Columbia. M Dobson, PhD, Armed Forces Institute of Pathology, District of Columbia. C Gaddy, MS, LA Pacha, MD, RL Mott, MD, T Hamilton, S Lee, MS, Y Liu, MD, PJ Weina, MD, PhD, M Krauss, MD, Walter Reed Army Institute of Research, Silver Spring, Maryland. P Gray, MSN, DP Dooley, MD, Brooke Army Medical Center, San Antonio, Texas. RD Bradshaw, MD, Uniformed Svcs Univ of the Health Sciences, Bethesda, Maryland. R Gibson, PhD, US Armed Forces Epidemiological Board. M Dorf, PhD, US Army 804th Medical Brigade. SA Tasker, MD, E Campbell, National Naval Medical Center; EM Kilbane, MD, Office of the Surgeon General of the US Navy. S Zobel, RL Erickson, MD, US Army Center for Health Promotion and Preventive Medicine; JM Rusnak, US Army Research Institute of Infectious Diseases. K Woodward, MD, Air Force Medical Support Agency; PA Mondloh, MA, Air Mobility Command; TL DiFato, MPH, Office of the Surgeon General of the US Air Force. EC McDonald, MD, GR Cox, MD, US Marine Corps. J Mansfield, MAS, V MacIntosh, MD, Global Emerging Infections Surveillance and Response System; K Cox, MD, Office of Health Affairs, US Dept of Defense. K Kubota, MPH, Div of Vector-Borne Infectious Diseases, National Center for Infectious Diseases, CDC.
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