Acinetobacter baumannii: emergence and spread in Israeli hospitals 1997-2002

Molecular and epidemiologic study of polyclonal outbreaks of multidrug-resistant Acinetobacter baumannii infection in an Israeli hospital

OBJECTIVES

To perform a molecular and epidemiologic investigation of multidrug-resistant (MDR) Acinetobacter baumannii in an institution were polyclonal outbreaks have been observed and determine whether these polyclonal outbreaks had an endogenous origin or were caused by in-hospital patient-to-patient transmission.

DESIGN

Retrospective analysis of prospectively collected data.

SETTING

An epidemiologic and genotypic investigation of incident cases of MDR A. baumannii infection in an Israeli university tertiary care center.

PATIENTS

Hospitalized patients with MDR A. baumannii isolated from clinical samples during a 13-week period, from April 15, 2003, through July 15, 2003.

INTERVENTION

All patients with new MDR A. baumannii infections were recruited, and isolates were typed using pulsed-field gel electrophoresis. Data on in-hospital movements and consultations were extracted from computerized databases. Quantification of transmission opportunities (TOPs), defined as encounters between an established carrier and a future carrier of MDR A. baumannii, and analysis of ward clusters were performed.

RESULTS

We studied 96 MDR A. baumannii isolates, which belonged to 18 different pulsed-field gel electrophoresis clones. In 65% of cases, TOPs involving patients with the same clone were demonstrated, which is significantly greater than the number of TOPs involving patients with different clones (P=.01).

CONCLUSION

Although outbreaks of MDR A. baumannii infection may be polyclonal, we believe that patient-to-patient transmission explains most cases of transmission. Polyclonal local outbreaks reflect several clonal outbreaks occurring simultaneously. The cause of polyclonal outbreaks of A. baumannii infections clustered by ward and time remains to be explained.

Outcomes of Acinetobacter baumannii infection in critically ill burned patients

The objective of this study was to determine the incidence of drug resistance among isolates of Acinetobacter baumannii from our Burn Intensive Care Unit (BICU), the rate of clinical cure, and the mortality rate. We undertook a retrospective review of all cases of infection from the BICU between January 2004 and November 2005. The group consisted of 24 men (80%) and 6 women with a mean age of 43 years (range, 17-76 years, +/-14.5 years). Mean TBSA burned was 43% (range, 9-75%, +/-19%). Mean BICU length of stay was 49 days (range, 5-118 days, +/-30 days). Patients developed their first infection after a mean of 16 days (5-73 days, +/-14 days). The initial site of infection was bronchoalveolar lavage in 21 (70%), blood in 6 (20%), central venous catheter tip in 2 (7%), and urine in 1 (3%). The isolates displayed resistance to imipenem in 87% of cases. No organism displayed resistance to colistin (polymixin E). Patients were treated with colistin in 20 cases (67%), with amikacin in 8 cases (27%), and with imipenem in 2 cases (7%). A total of 10 patients (33%) died, 1 from gastrointestinal bleeding and 9 from active infection, giving an infection related mortality of 30%. In 21 cases (70%), a cure was achieved with a mean duration of treatment of 16 days (range, 4-30 days, +/-7 days). The majority of A. baumannii isolates were multidrug resistant; however, no isolate displayed resistance to colistin. Cure rate was 70% and infection-related mortality reached 30%. More investigation is warranted to improve prevention and to assess new therapeutic agents.

Surveillance cultures and duration of carriage of multidrug-resistant Acinetobacter baumannii

Isolating carriers of multidrug-resistant (MDR) Acinetobacter baumannii is the main measure to prevent its spread. Identification of carriers accompanied by contact precautions is essential. We aimed to determine the appropriate surveillance sampling sites and the duration of carriage of MDR A. baumannii. We studied prospectively two groups of patients from whom MDR A. baumannii was previously isolated: (i) those with recent clinical isolation (<or=10 days) and (ii) those with remote clinical isolation (>or=6 months). Screening for carriage was conducted from six sites: nostrils, pharynx, skin, rectum, wounds, and endotracheal aspirates. Strains recovered concurrently from different sites were genotyped using pulsed-field gel electrophoresis. Twelve of 22 with recent clinical isolation of MDR A. baumannii had >or=1 positive screening culture, resulting in a sensitivity of 55% when six body sites were sampled. Sensitivities of single sites ranged from 13.5% to 29%. Among 30 patients with remote clinical isolation, screening cultures were positive in 5 (17%), with a mean duration of 17.5 months from the last clinical culture. Remote carriers had positive screening cultures from the skin and pharynx but not from nose, rectum, wounds, or endotracheal aspirates. Eleven strains from five patients were genotyped. In all but one case, isolates from different sites in a given patient were clonal. Current methodology is suboptimal to detect MDR A. baumannii carriage. The sensitivity of surveillance cultures is low, even when six different body sites are sampled. The proportion of individuals with previous MDR A. baumannii isolation who remain carriers for prolonged periods is substantial. These data should be considered when designing measures to limit the spread of MDR A. baumannii.

Attributable mortality of Acinetobacter baumannii infections in critically ill patients: a systematic review of matched cohort and case-control studies

INTRODUCTION

There has been a continuing controversy about whether infection with Acinetobacter baumannii increases morbidity and mortality independently of the effect of other confounding factors.

METHODS

We performed a systematic review of matched case-control and cohort studies examining the mortality attributable to infection with or acquisition of A. baumannii (infection or colonization). We included in our review studies that compared mortality and/or morbidity of patients with acquisition of or infection with A. baumannii (cases) with the outcomes of matched patients without A. baumannii isolation from clinical specimens (controls). The relevant studies were identified from searches of the PubMed and the Cochrane Library databases. Two independent reviewers performed the literature search, study selection, and data extraction from nine identified relevant studies.

RESULTS

The attributable mortalities, in the hospital and in the intensive care unit, of patients with A. baumannii infection in six matched case-control studies included in our review ranged from 7.8% to 23% and from 10% to 43%, respectively. In addition, a statistically significantly higher mortality was reported for patients with A. baumannii acquisition; that is, colonization or infection (cases) compared with controls without such an acquisition in all four reviewed studies that reported data on this comparison.

CONCLUSION

Although definitive statements about the mortality attributable to the acquisition of A. baumannii cannot be made from the available studies because of their methodological heterogeneity, the reviewed data suggest that infection with or acquisition of A. baumannii seems to be associated with increased mortality.

The significance of Acinetobacter baumannii bacteraemia compared with Klebsiella pneumoniae bacteraemia: risk factors and outcomes

Risk factors and outcomes for patients with nosocomial Acinetobacter baumannii bacteraemia were compared with those for patients with nosocomial Klebsiella pneumoniae bacteraemia in a single centre in Israel between 2000 and 2003. Data were collected retrospectively through patient chart review. In total, 112 patients with A. baumannii bacteraemia and 90 patients with K. pneumoniae bacteraemia were identified. A. baumannii was significantly associated with poorer performance status, mechanical ventilation, presence of devices, prior treatment with carbapenems, pneumonia as the source of infection and inappropriate empirical antibiotic treatment. All-cause 30-day mortality was higher for A. baumannii bacteraemia compared with K. pneumoniae bacteraemia (61.6% vs 38.9%, P=0.001). Variables significantly associated with mortality at the univariate level (P<0.1) were entered into a multi-variable logistic regression model for mortality. A. baumannii remained significantly associated with mortality when adjusted for all other risk factors (odds ratio 3.61, 95% confidence interval 1.55-8.39). This result did not change when the analysis was repeated for subgroups of less severely ill patients, i.e. those who were not ventilated and those who did not present with septic shock. These results support the view that nosocomial bacteraemia due to A. baumannii is associated with increased mortality.

Identification of Acinetobacter species and genotyping of Acinetobacter baumannii by multilocus PCR and mass spectrometry

Members of the genus Acinetobacter are ubiquitous in soil and water and are an important cause of nosocomial infections. A rapid method is needed to genotype Acinetobacter isolates to determine epidemiology and clonality during infectious outbreaks. Multilocus PCR followed by electrospray ionization mass spectrometry (PCR/ESI-MS) is a method that uses the amplicon base compositions to genotype bacterial species. In order to identify regions of the Acinetobacter genome useful for this method, we sequenced regions of six housekeeping genes (trpE, adk, efp, mutY, fumC, and ppa) from 267 isolates of Acinetobacter. Isolates were collected from infected and colonized soldiers and civilians involved in an outbreak in the military health care system associated with the conflict in Iraq, from previously characterized outbreaks in European hospitals, and from culture collections. Most of the isolates from the Iraqi conflict were Acinetobacter baumannii (189 of 216 isolates). Among these, 111 isolates had genotypes identical or very similar to those associated with well-characterized A. baumannii isolates from European hospitals. Twenty-seven isolates from the conflict were found to have genotypes representing different Acinetobacter species, including 8 representatives of Acinetobacter genomospecies 13TU and 13 representatives of Acinetobacter genomospecies 3. Analysis by the PCR/ESI-MS method using nine primer pairs targeting the most information-rich regions of the trpE, adk, mutY, fumC, and ppa genes distinguished 47 of the 48 A. baumannii genotypes identified by sequencing and identified at the species level at least 18 Acinetobacter species. Results obtained with our genotyping method were essentially in agreement with those obtained by pulse-field gel electrophoresis analysis. The PCR/ESI-MS genotyping method required 4 h of analysis time to first answer with additional samples subsequently analyzed every 10 min. This rapid analysis allows tracking of transmission for the implementation of appropriate infection control measures on a time scale previously not achievable.