Completely Resistant Acinetobacter baumannii Strains • Author(s): Siham Mahgoub , MD; Jimi Ahmed , RN; Aaron E. Glatt , MDSource: Infection Control and Hospital Epidemiology, Vol. 23, No. 8 (August 2002), pp. 477-479Published by: The University of Chicago Press on behalf of The Society for Healthcare Epidemiologyof AmericaStable URL: http://www.jstor.org/stable/10.1086/502091 .

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Vol. 23 No. 8 CONCISE COMMUNICATIONS 477

2. Hospital Infection Control Practices Advisory Committee. Recom-mendations for preventing the spread of vancomycin resistance. InfectControl Hosp Epidemiol 1995;16:105-113.

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6. Hacek DM, Bednarz P, Noskin GA, Zembower T, Peterson LR. Yield ofvancomycin-resistant enterococci and multidrug-resistant Entero-bacteriaceae from stools submitted for Clostridium difficile testing com-pared to results from a focused surveillance program. J Clin Microbiol2001;39:1152-1154.

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Completely Resistant Acinetobacterbaumannii Strains

Siham Mahgoub, MD; Jimi Ahmed, RN; Aaron E.Glatt, MD

ABSTRACTNosocomially acquired completely resistant Acinetobacter

baumannii strains are a major clinical concern. We identified com-pletely resistant A. baumannii in 6 (4.9%) of 122 A. baumannii iso-lates in a retrospective chart review at two teaching hospitals. Allof these patients had received broad-spectrum antibiotics and hadsevere underlying comorbid illnesses, long hospitalizations, orrecent surgical procedures; 3 had been in the intensive care unit.Five (83%) of the 6 patients were older than 70 years. Only onedeath occurred. Strict infection control measures may limit furtherspread (Infect Control Hosp Epidemiol 2002;23:477-479).

The incidence of nosocomially acquired multidrug-resistant Acinetobacter baumannii has been rising in thepast few years.1 Indeed, completely resistant A. baumanniistrains (ie, resistant to all antibiotics approved by the Foodand Drug Administration [FDA]) have surfaced and are areal challenge to the practicing physician. We conducted astudy to define the incidence, characteristics, and risk fac-tors of such completely resistant A. baumannii strains inour institution.

METHODS

A retrospective chart review of all patients with A.baumannii isolated from any body site in the year 2000 wasconducted in two community teaching hospitals (MaryImmaculate Hospital and St. John’s Hospital) in Queens,

New York. Patient demographics and factors that might beassociated with acquisition of completely resistant A. bau-mannii strains were identified. Completely resistant A. bau-mannii strains were defined as any A. baumannii isolateresistant to all FDA-approved antibiotics, as tested by a sin-gle laboratory using the VITEK system (bioMérieux, Inc.,Durham, NC). Standard susceptibility testing was per-formed on each isolate. All FDA-approved antibiotics withpotential A. baumannii activity were tested.

RESULTS

A. baumannii isolates were identified in 122 differentpatients. All 122 charts were reviewed. No patient had com-pletely resistant A. baumannii strains isolated from morethan one body site during the study year. Six patients (4.9%)had completely resistant A. baumannii strains isolated(Table 1). Five (83%) of the 6 patients were older than 70years (range, 46 to 91 years); 4 (67%) were women. Threeisolates (50%) were recovered from patients in the intensivecare unit (ICU), and 3 (50%) were from patients on a med-ical ward. Half of the isolates were detected in respiratoryspecimens and were clinically considered to be truepathogens; the other half were isolated in urine culturesand were considered to represent clinically insignificantcolonization. The time between admission and initial isola-tion of completely resistant A. baumannii strains was a min-imum of 1 month (range, 1 to 6 months) (Table 1).

Table 2 outlines the predominant findings associatedwith acquisition of completely resistant A. baumannii strains.In the three patients with completely resistant A. baumanniistrains detected in respiratory isolates, mechanical ventila-tion, antibiotic use within the month prior to isolation ofcompletely resistant A. baumannii (trimethoprim–sulfamethoxazole plus levofloxacin, imipenem, and cef-tazidime, respectively), and underlying cardiovascularcomorbidity were present. Underlying respiratory disease,prior nursing home residence, and tracheostomy were alsocommon (67%). All three of these patients underwent someform of antibiotic therapy. Patient 1 was treated with amikacinand ceftazidime, patient 2 was treated with trimethoprim–sul-famethoxazole (a prior wound culture grew A. baumanniisensitive to trimethoprim–sulfamethoxazole), and patient 3received amikacin plus ampicillin–sulbactam. One patient(33%) died during hospitalization. The other two patientswere discharged; one had persistently positive cultures andthe other did not have follow-up cultures.

In the three patients with completely resistant A. bau-mannii strains detected in urine isolates, prior antibiotic use(amikacin and imipenem, ceftazidime, and ceftazidime plusimipenem, respectively), underlying cardiovascular disease,and surgery during hospitalization were present. Foleycatheterization, underlying respiratory disease, and diabeteswere also common (67%). All patients survived without treat-ment and colonization was considered clinically unimportant.One urine culture spontaneously cleared, one patient hadcompletely resistant A. baumannii strains isolated for 2 con-secutive months and was considered chronically colonized,and the other patient had no follow-up cultures.

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478 INFECTION CONTROL AND HOSPITAL EPIDEMIOLOGY August 2002

ICU stay was a potential contributing factor to acqui-sition of completely resistant A. baumannii strains in threepatients. Completely resistant A. baumannii strains wereisolated from two respiratory specimens from the St. John’sHospital ICU (January and October 2000) and a urinary

specimen from Mary Immaculate Hospital (November2000). There were no obvious connections among thesethree patients, but a true extensive investigation of allpotential associations was not undertaken.

After a patient was identified as having completelyresistant A. baumannii, stricter infection control prac-tices were implemented, including placement on contactisolation (in addition to standard precautions) and use ofa single-bed room (for all non-ICU patients and some ICUpatients). Additionally, specific education was provided tothe staff, laboratory records were reviewed daily toimmediately identify and isolate any new cases, and dis-charge of the patient with completely resistant A. bau-mannii was attempted as soon as clinically feasible.Various treatment regimens were attempted. No newcases were reported in the 6 months after the November2000 isolate. Since then, we have continued to encounterisolated cases, however.

DISCUSSION

Nosocomially acquired multidrug-resistant A. bau-mannii and specifically completely resistant A. baumanniistrains present a real challenge to hospital epidemiologistsand treating physicians. Prolonged hospitalization (espe-cially prolonged ICU stay)1 and mechanical ventilation2,3

have been shown to be important risk factors for acquisi-tion of resistant A. baumannii. All of our patients hadextended hospitalization or ICU stay as a risk factor, andall of the respiratory specimens growing completely resis-tant A. baumannii strains were from patients receivingmechanical ventilation (and frequently also with tra-cheostomies).

Not surprisingly, antibiotics play a premier role in thedevelopment of nosocomial A. baumannii colonization.Husni et al.4 reported ceftazidime use as being associatedwith acquisition of A. baumannii. Villers et al.5 identifiedquinolones as a risk factor, and Manikal et al.6 noted theemergence of imipenem-resistant A. baumannii whenimipenem was used to treat Klebsiella infections resistant tocephalosporins. All of our patients had recently receivedbroad-spectrum antibiotics, which undoubtedly changedambient colonizing flora and predisposed them to acquisi-

TABLE 1CHARACTERISTICS OF PATIENTS WITH COMPLETELY RESISTANT ACINETOBACTER BAUMANNII STRAINS

Months FromInfection Versus Admission

Isolate Age (y) Gender Specimen Source Patient Location Colonization to Acquisition

1 46 F Respiratory ICU I 62 71 M Respiratory Medical ward I 53 83 M Respiratory ICU I 14 91 F Urinary Medical ward C 15 70 F Urinary ICU C 26 70 F Urinary Medical ward C 3

ICU = intensive care unit; I = infection; C= colonization.

TABLE 2ASSOCIATED FINDINGS AMONG PATIENTS WITH COMPLETELY

RESISTANT ACINETOBACTER BAUMANNII STRAINS

Finding No. %%

Respiratory isolatesMechanical ventilation 3 100Tracheostomy 2 67Prior hospitalization 0 0Nursing home residence 2 67Recent antibiotic use 3 100Recent steroid use 1 33Comorbid conditions

Surgery during this 0 0hospitalization

Respiratory 2 67Cardiovascular 3 100Neurologic 0 0Malignancy 1 67Diabetes 0 0

Urinary isolatesFoley catheter 2 67Prior hospitalization 0 0Nursing home residence 0 0Recent antibiotic use 3 100Recent steroid use 0 0Comorbid conditions

Surgery during this 2 67hospitalization

Respiratory 2 67Cardiovascular 3 100Neurologic 0 0Malignancy 0 0Diabetes 2 67

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Vol. 23 No. 8 CONCISE COMMUNICATIONS 479

tion of completely resistant A. baumannii strains. Judiciousantibiotic use is essential to prevent development of com-pletely resistant A. baumannii strains.

Baraibar et al.7 concluded that certain comorbid con-ditions were not significantly associated with acquiringresistant A. baumannii strains. However, our studydemonstrated that recent surgery, Foley catheterization ortracheostomy during hospitalization, underlying cardio-vascular and respiratory diseases, and nursing home resi-dence prior to admission were common among thepatients with completely resistant A. baumannii strains.Villers et al.5 also noted increased A. baumannii coloniza-tion after a surgical procedure, but that was apparentlyrelated to an epidemic associated with a new operatingroom. Male gender has also been purported to be a con-tributing factor,8 but our study demonstrated a slightfemale predominance.

Okpara and Maswoswe9 demonstrated that coloniza-tion with resistant A. baumannii strains could lead to seri-ous infection. Fifty percent of the isolates in our study weredeemed true pathogens by the treating clinician, with a 33%mortality rate noted. Our numbers are too small to make adefinitive statement, but this coincides with other studiesthat reported an ICU mortality rate among patients withresistant A. baumannii of between 23% and 71%.10

Intuitively, patients with serious infections caused by high-ly resistant if not completely resistant bacteria certainlyhave a poor prognosis. However, colonization with com-pletely resistant A. baumannii strains does not necessarilyportend a worse outcome and only appears to be a markerassociated with certain risk factors. Because there is noclear indication, attempts at treatment (if even available)should be withheld pending studies demonstrating anybenefit from reducing the incidence of colonization.

Colonization with completely resistant A. baumanniistrains is a new problem in our hospital. Strict attention totight infection control practices was essential in controlling

initial spread, but the problem is not going to vanish.Vigilance, treatment only if indicated, strict infection con-trol methods, and discharge from the hospital as soon aspossible are essential if we are to prevent this problem frombecoming even more widespread than it already is.

Drs. Mahgoub and Glatt are from the Division of InfectiousDiseases and Ms. Ahmed and Dr. Glatt are from the Department ofInfection Control, St. Vincent Catholic Medical Centers of New York,Brooklyn/Queens Region, Jamaica, New York. Dr. Glatt is also from theNew York Medical College, Valhalla, New York.

Address reprint requests to Aaron E. Glatt, MD, St. VincentCatholic Medical Centers, Brooklyn/Queens Service Division, 88-25 153Street, Suite 3-R, Jamaica, NY 11432.

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