This study is a retrospective review of a city hospital epidemiology data base and includes isolates of Acinetobacter baumannii AB from patients. Multidrug resistant Acinetobacter baumannii was defined as resistance to more than three classes of antibiotics.
As in medical patients, the isolation of Acinetobacter from multiple sites and the need for mechanical ventilation were significantly associated with the development of MRAB. The factors significantly associated with MRAB in both the general patient population and surgical patients were mechanical ventilation and the recovery of Acinetobacter from multiple anatomic sites. Previous antibiotic use and neurologic impairment were significant factors in medical patients.
Colonization or infection with MRAB is associated with increased mortality. Peer Review reports. Acinetobacter baumannii , found ubiquitously in the environment, is an aerobic gram negative rod which is a non-fermenter of glucose. When stationary, AB appears as a coccobacillus, however during growth it takes on a rod form. Multidrug resistant Acinetobacter baumannii is an important cause of hospital acquired infection and has been shown in some studies to increase mortality and length of stay [ 1 ].
Multidrug Resistant Acinetobacter baumannii is often associated with co-infection by other virulent pathogens. Thus it is difficult to determine its attributable mortality. Though MRAB is considered to be a hospital acquired infection, patients occasionally present with community acquired colonization of chronic wounds.
In order to provide timely and proper antibiotic therapy it is important to know the characteristics of those patients with colonization and invasive infection with MRAB. The source of infection and the prevalence of co-infecting pathogens will also be investigated.
This study is a retrospective review of a city hospital epidemiology data base and includes isolates of AB from patients. For the period through a retrospective chart review was performed on all patients with AB isolates.
The patients were identified through the hospital infection control data base. Documented patient demographics and potential risk factors included diagnosis, length of stay, patient location, age, sex, race, previous institutionalization, previous antibiotic use, mechanical ventilation, tracheostomy, and underlying co-morbidity.
The source of the AB isolates was also noted as well as the patient outcome. Previous institutionalization included prior hospitalization, nursing home residency, or incarceration within 90 days of a positive AB culture date. Prior antibiotic use was noted for those patients who received an antibiotic within one month of the AB isolation.
The resistance patterns of all isolates were included in the analysis; however patients with more than one isolate were counted only once. The source of the AB isolate is the anatomic site where the culture was obtained. The identification of the isolates as Acinetobacter and susceptibility testing of those isolates was performed using a Siemens formerly Dade Behering microscan system, which is FDA approved for this use in clinical laboratories.
Testing was performed according to manufacturer specifications for this instrument and was done in accordance with NCCLS recommended practices. This instrument makes use of broth microdilution methodology to determine resistance. An isolate was deemed pan-sensitive if it was sensitive to all commonly tested antibiotics except colistin and highly sensitive if it was sensitive to imipenem, amikacin, and ampicillin-sulbactam.
The isolate was considered highly resistant if it was resistant to imipenem, amikacin, and ampicillin-sulbactam. An isolate was classified as pan-resistant if it was resistant to all commonly used antibiotics. Multidrug resistant Acinetobacter baumannii isolates are defined as those resistant to more than three classes of antibiotics. This study is designed to document the risk factors for the isolation of MRAB in our surgical patient population, thus no attempt was made to distinguish between colonization and invasive infection.
The differences between groups were determined by Student's T-test for continuous data or the Fisher's exact test for categorical data 2-tailed. Multidrug resistant Acinetobacter baumannii is defined as resistance to more than three classes of antibiotics. This is intriguing as these antibiotics were formerly very effective against AB. The sources of AB isolates in all patients are shown in Table 1. The major site of AB isolation in this study was the respiratory tract.
Due to the inconsistency of obtaining quantitative cultures it was not possible to determine infection vs. Among the positive wound isolates the majority were from chronic diabetic wounds, amputation sites, and decubitus ulcers. The factors which were significantly associated with multidrug resistance include the recovery of Acinetobacter from multiple sites, mechanical ventilation, previous antibiotic use, and the presence of co-morbidity especially neurologic impairment.
Diabetes mellitus and the previous use of quinolones trended toward significance. The sites of AB isolation in surgical patients were wounds 36 The mean length of stay for sensitive and multidrug resistant Acinetobacter 32 vs. Acinetobacter baumannii has become an important pathogen in recent years and has been shown to increase morbidity and mortality [ 1 — 3 ].
The definition of MRAB varies in the literature, but several authorities consider an isolate to be multidrug resistant if it is resistant to three or more classes of antibiotics [ 4 ]. The factors associated with the isolation of AB in our combined medical and surgical patient groups include mechanical ventilation, previous antibiotic therapy, co-morbidity, especially neurologic impairment, and multiple Acinetobacter isolates.
The significant factors for MRAB in the surgical group were mechanical ventilation, multiple isolates, and neurologic impairment. These findings are consistent with other reports [ 6 — 9 ]. The prior exposure to quinolones trended toward significance which is documented in previous reports [ 10 ]. Several investigators have found an association of MRAB with co-morbidities [ 7 ].
Our patients had significant rates of diabetes mellitus, cardiovascular disease, chronic obstructive lung disease and neurological impairment. Most CRAB infections are healthcare-associated infections HAIs occurring in people who have underlying medical conditions or certain types of healthcare exposures, such as: Immunocompromising conditions.
Recent frequent or prolonged stays in health care settings. Invasive medical devices such as breathing tubes, feeding tubes, and central venous catheters. Open wounds from surgery. A history of taking certain antibiotics for long periods of time.
This circumstance is not explained by differences in infection control measures recommended; during the entire study period this included contact isolation of every patient from whom MDR A. On certain floors surveillance nose, forearms, armpits, and perirectal swabs and environmental cultures using swabs, contact plates, and direct culturing of fluids were performed to try and identify a reservoir of organism.
In this study, case-patients and controls were matched by ward and calendar time to focus on individual risk factors and not on differences between wards and temporal changes. Figure 3. A typical pulsed-field gel electrophoresis analysis of selected isolates of A. Lanes 11—13 are of strains not We identified 10 distinct clones of A. Figure 3 shows 6 different PFGE-defined clones, each having from 1 to 4 subtypes showing a 1- to 2-band difference.
Two of the 10 different clones dominated: 22 case-patients had clone A and 10 case-patients had clone B, although no specific clone dominated in a specific ward but rather each clone was spread among several wards during the entire study period Table 1. We also found various antimicrobial drug susceptibility phenotypes all belonging to our definition of MDR within each PFGE clone, but almost all cases of carbapenem resistance belonged to clone A. Case-patients were similar to their matched control patients with respect to mean age The groups were also similar in habits of smoking and alcohol consumption and in the occurrence of coexisting conditions of lung disease, diabetes, kidney, liver disease, malignancy, and posttransplantation condition.
Hospital events before study entry differed between case-patients and controls. Case-patients were more likely to have received mechanical ventilation OR 2. They were less likely to have had another bedside surgical procedure before the isolation of A. Several variables tended to be more associated with case-patients, but the values did not reach statistical significance: admission from another institute OR 2.
A matched multivariate model, adjusted for the hospital length of stay, was developed by using conditional logistic regression Table 3.
The variables that were identified by this model as being significant risk factors for MDR A. Two agents used in the hospital were associated with MDR A.
We sought to understand the epidemiology of MDR A. Our findings illustrated its complex epidemiology and delineated individual risk factors. The complex epidemiology may explain the difficulties encountered in controlling the emergence of this nosocomial pathogen. Almost all cases of MDR A. The MDR A. Clones did not cluster in place i. Moreover, when an increase in incidence was observed in a certain ward, the increase was not associated with a single clone, and up to 4 different clones were present concomitantly in a ward.
We also found antimicrobial susceptibility profile variation within clones and similarities between clones, which showed that susceptibility pattern was not a useful marker for clonality. This finding illustrates well the complexity of the epidemiology of this nosocomial pathogen. Even with molecular typing data, determining the modes of spread of this organism was difficult, partly because we did not have a complete collection of the isolates.
Despite our expending extensive effort, we were unable to determine the source of these resistant strains. Although we believe that patient-to-patient transmission through contaminated hands of healthcare workers and fomites is the main route by which these MDR organisms spread, the combined epidemiologic and molecular data did not directly support this hypothesis.
Alternative explanations, such as repeated entry import of the same clone to the hospital ecosystem at various times and locations e. The individual risk factors for isolation of MDR A. We hypothesize that these associations may be related to the following factors: 1 patient-to-patient transmission within multipatient rooms patients who are segregated by sex and need for intensive monitoring ; 2 use of certain nonantimicrobial medication, such as calcium channel blockers, which may predispose for adherence or invasiveness by affecting the host or the pathogens 32 , 33 ; and 3 hormonal or other sex differences which may predispose a person for colonization and infection.
These hypotheses are currently being studied in our facilities. The multivariate analysis did not identify admission from another institution as a significant risk factor.
This probably relates to the small number and proportion of patients admitted from other institutions who were identified to be carriers of MDR A. These few patients may, however, have played an important role to the entrance of new clones and the spread of the organisms within our institution.
Moreover, case-patients that are not detected may still be important in the spread of these organisms. The administration of penicillin had a protective effect against isolation of MDR A. This protective effect was significant after confounding by multivariate analysis was controlled for. Penicillins lack activity against these MDR strains, and the protective effect cannot relate to sulbactam, since a sulbactam combination is seldom used in our institution.
To the best of our knowledge, such an effect has not been observed previously. Specific penicillins may possibly cause specific changes in the microflora that oppose colonization and growth of Acinetobacter spp. As for many other resistant organisms, metronidazole was a significant risk factor for MDR A. The observation that carbapenem resistance was much more frequent in the dominant clone could suggest that this phenotype may have contributed to the evolutionary success of the clone.
A previous study clearly demonstrated that the epidemiology and risk factors may vary for different clones This finding may lead to a dilution of effects and even to opposing effects by some risk factors. In our study, we did not analyze clone-specific risk factors because we did not believe that we truly had an epidemic clone and because the number of patients affected by each clone was too small to allow a statistically significant comparison.
Temporospatial factors, although they undoubtedly have an important role in the spread of resistant organisms, were not within the scope of this study. We controlled for these factors by the study design, i. Confounding may, however, have been introduced to our study by factors for which we did not control, such as residing in a multipatient room next to a patient with MDR A.
We used risk set sampling by matching for time at risk but did not allow case-patients to be eligible to be controls before to becoming cases. Since no clustering in time and place occurred, and controls were chosen from 35, admitted patients, this method of sampling should not have yielded biased results.
Despite the large number of cases that we identified, we were unable to understand the mode of spread and the reason for emergence of these organisms in our institution.
This fact may be because only some of the isolates were available for typing or because of the complex mode of spread in our hospital. Further study will be required to more fully understand the intricate phenomenon of MDR A. Abbo is in clinical development at Biosense Webster Israel. This work was part of his MSc dissertation in internal medicine. His primary research interests include the clinical epidemiology of infectious diseases and cardiology.
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