By Lisa Maragakis, MD

The Organism

• Acinetobacter are encapsulated, aerobic, non-fermentative gram-negative bacilli.
• Acinetobacter species are ubiquitous, living in soil and water. The organism can survive for extended periods in the environment and tolerates both wet and dry conditions.(1)
• Acinetobacter utilizes a wide variety of carbon and other energy sources and grows well on routine laboratory media. A tendency to retain crystal violet can lead to incorrect identification as gram-positive cocci. (2)
• There are over 20 species of Acinetobacter, though the species Acinetobacter baumannii accounts for >80% of isolates causing human disease.(2)
• The organism can survive for months on clothing and bedclothes, bed rails, ventilators and other surfaces in the environment, including sinks and doorknobs, making nosocomial transmission extremely difficult to control.

Epidemiology

• Acinetobacter baumannii is primarily a healthcare-associated pathogen. It is increasingly reported as the cause of outbreaks and nosocomial infections such as blood-stream infections, ventilator-associated pneumonia, urinary tract infections and wound infections.(3;4)
• Acinetobacter isolates demonstrate increasing resistance to commonly prescribed antimicrobials.(5) Multidrug-resistant Acinetobacter baumannii has been reported worldwide and is now recognized as one of the most difficult healthcare-associated infections to control and treat.(3)
• In a report of a citywide clonal outbreak in New York City, 53% of A. baumannii were resistant to carbapenems while 12% were resistant to all standard antimicrobial agents.(6)
• Multidrug-resistant Acinetobacter rarely causes serious infection in otherwise healthy people, and therefore poses minimal threat to healthcare workers or patients’ family members. Pregnant healthcare workers are not at increased risk from this organism, and can therefore care for patients infected or colonized with the organism.
• Outbreaks are frequently located in intensive-care units and burn units involving patients on mechanical ventilation.(4) Sources of transmission identified in the outbreak setting include predominately respiratory equipment such as resuscitator bags, valves, ventilator circuits, spirometers, peak flow meters, suction catheters, etc. Other sources include humidifiers, warming baths, multidose vials, distilled water, pillows, mattresses, bedpans, showers and water faucet aerators. No source was identified in approximately 50% of reported outbreaks.(4)
• An outbreak of MDR Acinetobacter at our institution was linked to the use of a pulsatile lavage with suction device for wound care. Widespread environmental contamination and healthcare-associated transmission of the organism occurred during this outbreak. As a result, The Hospital Epidemiology and Infection Control Department at The Johns Hopkins Hospital has implemented new infection control precautions that are followed for all pulsatile lavage with suction treatments. Click HERE to view/download the Infection Control Precautions for Pulsatile Lavage with Suction Treatment.
• Risk factors for colonization or infection with multidrug-resistant Acinetobacter include length of hospital stay, surgery, wounds, treatment with broad-spectrum antibiotics, parenteral nutrition, indwelling catheters, mechanical ventilation, and admission to an intensive care unit.(2;7;8)

Diagnosis

• Infection or colonization with Acinetobacter is usually diagnosed by clinical culture of blood, sputum, urine, wound, sterile body fluid, etc. Microbiologic cultures can be processed by standard methods on routine media.
• Antimicrobial susceptibility can be determined by various means, with the agar-dilution method being the gold-standard.
• Definitions for “multidrug-resistance” vary widely in the published literature. At our institution, multidrug-resistant Acinetobacter is defined as an isolate that is susceptible to no more than one class of antimicrobial agents, excluding colistin. (e.g. most isolates that meet our definition are completely resistant to commonly prescribed antibiotics or are susceptible to only the aminoglycoside class of agents).

Treatment

• Carbapenems (Imipenem and Meropenem) are the mainstay of treatment for antimicrobial-resistant gram-negative infections, though carbapenem-resistant Acinetobacter is increasingly reported.(6)
• Resistance to the carbapenem class of antibiotics makes multidrug-resistant Acinetobacter infections difficult, if not impossible, to treat.
• Colistin and polymyxin B have been used to treat highly resistant Acinetobacter infections.(9;10) The choice of appropriate therapy is further complicated by the toxicity of colistin which is mainly renal.(10) Acinetobacter isolates resistant to colistin and polymyxin B have also been reported.(11;12)
• Studies have demonstated in-vitro susceptibility of multidrug-resistant Acinetobacter to various synergistic combinations of antimicrobials including carbapenems, colistin, rifampin, and ampicillin-sulbactam.(10;13;14) The clinical utility of these combinations against pan-resistant Acinetobacter remains to be determined.

Prevention

• The costs associated with control of an outbreak can be staggering, and some institutions have been forced to close entire units in order to interrupt transmission of Acinetobacter.(3;15) Therefore, there is great incentive to prevent transmission in the healthcare setting and keep the organism from becoming endemic in an institution.
• As with prevention of any healthcare-associated organism, careful hand hygiene should be performed at all appropriate times– either hand washing at the sink or using an alcohol based hand sanitizer. Standard precautions should be followed at all times.
• The utility of active surveillance cultures to detect patients who are colonized with multidrug-resistant Acinetobacter remains to be determined.
• Measures reported to be successful in control of outbreaks include isolation precautions for infected or colonized patients, reinforcement hand hygiene, cohorting of patients, cohorting of staff, environmental disinfection, antimicrobial control, and unit closure.(4)
• At our institution, patients infected or colonized with multidrug-resistant Acinetobacter are placed in a private room on Maximum Isolation Precautions (Click here for the Isolation policy). We have also developed a Plan for the Prevention and Control of Multidrug-Resistant Acinetobacter. (click here for the prevention plan) which includes staffing guidelines, cleaning and disinfection guidelines, and a plan for cohorting staff and patients.

Links Of Interest

Plan for the Control and Prevention of Multidrug-Resistant Acinetobacter

Cleaning Protocol

Staffing Guidelines

Isolation Policy

Patient and Visitor Information Sheet

RN Fast Facts Sheet

References

1. Jawad A, Heritage J, Snelling AM, Gascoyne-Binzi DM, Hawkey PM. Influence of relative humidity and suspending menstrua on survival of Acinetobacter spp. on dry surfaces. J Clin Microbiol 1996; 34(12):2881-2887.
2. Allen D, Hartman B. Acinetobacter Species. In: Mandell GL, Bennett JE, Dolin R, editors. Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases. Philadelphia: Churchill Livingstone, 2000: 2339-2344.
3. Urban C, Segal-Maurer S, Rahal JJ. Considerations in control and treatment of nosocomial infections due to multidrug-resistant Acinetobacter baumannii. Clin Infect Dis 2003; 36(10):1268-1274.
4. Villegas MV, Hartstein AI. Acinetobacter outbreaks, 1977-2000. Infect Control Hosp Epidemiol 2003; 24(4):284-295.
5. Wisplinghoff H, Edmond MB, Pfaller MA, Jones RN, Wenzel RP, Seifert H. Nosocomial bloodstream infections caused by Acinetobacter species in United States hospitals: clinical features, molecular epidemiology, and antimicrobial susceptibility. Clin Infect Dis 2000; 31(3):690-697.
6. Landman D, Quale JM, Mayorga D, Adedeji A, Vangala K, Ravishankar J et al. Citywide clonal outbreak of multiresistant Acinetobacter baumannii and Pseudomonas aeruginosa in Brooklyn, NY: the preantibiotic era has returned. Arch Intern Med 2002; 162(13):1515-1520.
7. Chastre J, Trouillet JL. Problem pathogens (Pseudomonas aeruginosa and Acinetobacter). Semin Respir Infect 2000; 15(4):287-298.
8. Bergogne-Berezin E, Towner KJ. Acinetobacter spp. as nosocomial pathogens: microbiological, clinical, and epidemiological features. Clin Microbiol Rev 1996; 9(2):148-165.
9. Levin AS, Barone AA, Penco J, Santos MV, Marinho IS, Arruda EA et al. Intravenous colistin as therapy for nosocomial infections caused by multidrug-resistant Pseudomonas aeruginosa and Acinetobacter baumannii. Clin Infect Dis 1999; 28(5):1008-1011.
10. Giamarellos-Bourboulis EJ, Xirouchaki E, Giamarellou H. Interactions of colistin and rifampin on multidrug-resistant Acinetobacter baumannii. Diagn Microbiol Infect Dis 2001; 40(3):117-120.
11. Manikal VM, Landman D, Saurina G, Oydna E, Lal H, Quale J. Endemic carbapenem-resistant Acinetobacter species in Brooklyn, New York: citywide prevalence, interinstitutional spread, and relation to antibiotic usage. Clin Infect Dis 2000; 31(1):101-106.
12. Rhomberg PR, Jones RN, Sader HS. Results from the Meropenem Yearly Susceptibility Test Information Collection (MYSTIC) Programme: report of the 2001 data from 15 United States medical centres. Int J Antimicrob Agents 2004; 23(1):52-59.
13. Higgins PG, Wisplinghoff H, Stefanik D, Seifert H. In vitro activities of the beta-lactamase inhibitors clavulanic acid, sulbactam, and tazobactam alone or in combination with beta-lactams against epidemiologically characterized multidrug-resistant Acinetobacter baumannii strains. Antimicrob Agents Chemother 2004; 48(5):1586-1592.
14. Yoon J, Urban C, Terzian C, Mariano N, Rahal JJ. In vitro double and triple synergistic activities of Polymyxin B, imipenem, and rifampin against multidrug-resistant Acinetobacter baumannii. Antimicrob Agents Chemother 2004; 48(3):753-757.
15. Simor AE, Lee M, Vearncombe M, Jones-Paul L, Barry C, Gomez M et al. An outbreak due to multiresistant Acinetobacter baumannii in a burn unit: risk factors for acquisition and management. Infect Control Hosp Epidemiol 2002; 23(5):261-267.