Lizzie J. Harrell

Infective Endocarditis Due to Staphylococcus aureus: 59 Prospectively Identified Cases with Follow-up

Fifty-nine consecutive patients with definite Staphylococcus aureus infective endocarditis (IE) by the Duke criteria were prospectively identified at our hospital over a 3-year period. Twenty-seven (45.8%) of the 59 patients had hospital-acquired S. aureus bacteremia. The presumed source of infection was an intravascular device in 50.8% of patients. Transthoracic echocardiography (TTE) revealed evidence of IE in 20 patients (33.9%), whereas transesophageal echocardiography (TEE) revealed evidence of IE in 48 patients (81.4%). The outcome for patients was strongly associated with echocardiographic findings: 13 (68.4%) of 19 patients with vegetations visualized by TTE had an embolic event or died of their infection vs. five (16.7%) of 30 patients whose vegetations were visualized only by TEE (P < .01). Most patients with S. aureus IE developed their infection as a consequence of a nosocomial or intravascular device-related infection. TEE established the diagnosis of S. aureus IE in many instances when TTE was nondiagnostic. Visualization of vegetations by TTE may provide prognostic information for patients with S. aureus IE.

Recurrent Staphylococcus auveus Bacteremia: Pulsed-Field Gel Electrophoresis Findings in 29 Patients

To identify risk factors for relapse among 309 prospectively identified cases of Staphylococcus aureus bacteremia, patients with recurrent S. aureus bacteremia were identified, and pulsed-field gel electrophoresis (PFGE) was performed on isolates from both episodes. PFGE banding patterns from both isolates were identical in 23 patients, consistent with relapsed infection. Patients with PFGE-confirmed relapse were more likely by both univariate and multivariate analyses to have an indwelling foreign body (odds ratio [OR]=18.2, 95% confidence interval [CI]=7. 6-43.6; P<.001), to have received vancomycin therapy (OR=4.1, 95% CI=1.5-11.6; P=.008), or be hemodialysis-dependent (OR=4.1, 95% CI=1. 8-9.3; P=.002) than patients who did not develop recurrent bacteremia. These results suggest that recurrent episodes of S. aureus bacteremia are primarily relapses and are associated with an indwelling foreign body, receiving vancomycin therapy, and hemodialysis dependence.

National Survey on the Susceptibility of Bacteroides fragilis Group: Report and Analysis of Trends in the United States from 1997 to 2004

ABSTRACT The susceptibility trends for the species of the Bacteroides fragilis group against various antibiotics from 1997 to 2004 were determined by using data for 5,225 isolates referred by 10 medical centers. The antibiotic test panel included ertapenem, imipenem, meropenem, ampicillin-sulbactam, piperacillin-tazobactam, cefoxitin, clindamycin, moxifloxacin, tigecycline, chloramphenicol, and metronidazole. From 1997 to 2004 there were decreases in the geometric mean (GM) MICs of imipenem, meropenem, piperacillin-tazobactam, and cefoxitin for many of the species within the group. B. distasonis showed the highest rates of resistance to most of the β-lactams. B. fragilis, B. ovatus, and B. thetaiotaomicron showed significantly higher GM MICs and rates of resistance to clindamycin over time. The rate of resistance to moxifloxacin of B. vulgatus was very high (MIC range for the 8-year study period, 38% to 66%). B. fragilis, B. ovatus, and B. distasonis and other Bacteroides spp. exhibited significant increases in the rates of resistance to moxifloxacin over the 8 years. Resistance rates and GM MICs for tigecycline were low and stable during the 5-year period over which this agent was studied. All isolates were susceptible to chloramphenicol (MICs < 16 μg/ml). In 2002, one isolate resistant to metronidazole (MIC = 64 μg/ml) was noted. These data indicate changes in susceptibility over time; surprisingly, some antimicrobial agents are more active now than they were 5 years ago.

Lessons Learned from the Anaerobe Survey: Historical Perspective and Review of the Most Recent Data (2005–2007)

BACKGROUND The rationale and lessons learned through the evolution of the National Survey for the Susceptibility of Bacteroides fragilis Group from its initiation in 1981 through 2007 are reviewed here. The survey was conceived in 1980 to track emerging antimicrobial resistance in Bacteroides species. METHODS Data from the last 11 years of the survey (1997-2007), including 6574 isolates from 13 medical centers, were analyzed for in vitro antimicrobial resistance to both frequently used and newly developed anti-anaerobic agents. The minimum inhibitory concentrations of the antibiotics were determined using agar dilution in accordance with Clinical and Laboratory Standards Institute recommendations. RESULTS The analyses revealed that the carbapenems (imipenem, meropenem, ertapenem, and doripenem) and piperacillin-tazobactam were the most active agents against these pathogens, with resistance rates of 0.9%-2.3%. In the most recent 3 years of the survey (2005-2007), resistance to some agents was shown to depend on the species, such as ampicillin-sulbactam against Bacteroides distasonis (20.6%) and tigecycline against Bacteroides uniformis and Bacteroides eggerthii ( approximately 7%). Very high resistance rates (>50%) were noted for moxifloxacin and trovafloxacin, particularly against Bacteroides vulgatus. During that period of study, non-B. fragilis Bacteroides species had >40% resistance to clindamycin. Metronidazole-resistant Bacteroides strains were also first reported during that period. CONCLUSIONS In summary, resistance to antibiotics was greater among non-B. fragilis Bacteroides species than among B. fragilis and was especially greater among species with a low frequency of isolation, such as Bacteroides caccae and B. uniformis. The emergence of resistance among the non-B. fragilis Bacteroides species underscores the need for speciation of B. fragilis group isolates and for clinicians to be aware of associations between species and drug resistance.

Contrasting Methicillin-Resistant Staphylococcus aureus Colonization in Veterans Affairs and Community Nursing Homes

PURPOSE To compare the prevalence of methicillin-resistant Staphylococcus aureus (MRSA) nares colonization, the patterns of MRSA acquisition, and the risk for subsequent MRSA infection between a hospital-based, Department of Veterans Affairs (VA) nursing home care unit (NHCU) and community-based nursing homes. PATIENTS AND METHODS In this prospective study, 148 residents of three community nursing homes and 55 residents of a VA NHCU had their anterior nares swabbed; repeat cultures were obtained from hospitalized patients and/or individuals colonized with MRSA. Subjects were followed up prospectively for 1 year to note hospitalizations and the development of MRSA infections. RESULTS The prevalence of MRSA colonization was significantly higher in the VA NHCU than in the community nursing homes (mean +/- SD 30.3% +/- 11% versus 9.9% +/- 4%). The rate of MRSA nares colonization was similar in the two settings. Acquisition of MRSA took place in both the long-term care facilities and hospitals, with 23.8% of incident cases occurring during a hospitalization. Only 3 of the 27 individuals colonized at baseline developed an MRSA infection. A trend toward an increased rate of infection was seen in colonized individuals residing in the community nursing homes versus those in the VA NHCU (relative risk 4.67; 95% Cl 0.55 to 39.9). Forty-seven percent of the 55 subjects hospitalized were colonized at some point during the study. In contrast to residents of the VA NHCU, MRSA colonization in the community facilities was a marker for high mortality. CONCLUSIONS Outcomes from colonization may be different in the VA NHCU population and the community nursing home population.

National Survey on the Susceptibility of Bacteroides fragilis Group: Report and Analysis of Trends for 1997-2000

The results of a multicenter US survey using the National Committee for Clinical Laboratory Standards currently recommended methodology for measuring in vitro susceptibility of 2673 isolates of Bacteroides fragilis group species were compared from 1997 to 2000. The test panel consisted of 14 antibiotics: 3 carbapenems, 3 beta-lactam-beta-lactamase inhibitors, 3 cephamycins, 2 fluoroquinolones, clindamycin, chloramphenicol, and metronidazole. Declines in the geometric mean minimum inhibitory concentrations were seen with imipenem, meropenem, ampicillin-sulbactam, and the cephamycins. Increased geometric means were observed with the fluoroquinolones and were usually accompanied by an increase in resistance rates. Bacteroides distasonis shows the highest resistance rates among beta-lactam antibiotics, whereas Bacteroides vulgatus shows the highest resistance levels among fluoroquinolones. B. fragilis shows the lowest resistance rates for all antibiotics. All strains were susceptible to chloramphenicol and metronidazole concentrations <8 microgram/mL. The data underscore the need for species identification and continued surveillance to monitor resistance patterns.

Update on resistance of Bacteroides fragilis group and related species with special attention to carbapenems 2006-2009.

The susceptibility trends for the species of the Bacteroides fragilis group against various antibiotics were determined using data from 4 years [2006-2009] on 1957 isolates referred by 8 medical centers participating in a National Survey for the Susceptibility of B. fragilis. The antibiotic test panel included doripenem, ertapenem, imipenem, meropenem, ampicillin:sulbactam, piperacillin:tazobactam, cefoxitin, clindamycin, moxifloxacin, tigecycline, chloramphenicol and metronidazole. MICs were determined using agar dilution methods following CLSI recommendations. Genetic analysis of isolates from 2008 with elevated MICs (>2 μg/mL) to one or more of the carbapenems to detect presence of the cfiA gene was performed using PCR methodology. The results showed an increase in the resistance rates to the β-lactam antibiotics. High resistance rates were seen for clindamycin and moxifloxacin (as high as 60% for clindamycin and >80% for moxifloxacin), with relatively stable low resistance (5.4%) for tigecycline. For carbapenems, resistance in B. fragilis was 1.1%-2.5% in 2008-9. One isolate resistant to metronidazole (MIC 32 μg/mL) was observed as well as isolates with elevated MICs to chloramphenicol (16 μg/mL). Genetic analysis indicated that the cfiA gene was present in some but not all of the isolates with high MICs to the carbapenems. These data indicate that there continue to be changes in susceptibility over time, and that resistance can be seen among the carbapenems. High antibiotic resistance rates tend to be associated with specific species.

Predictors of mortality in patients with bloodstream infection due to ceftazidime-resistant Klebsiella pneumoniae.

ABSTRACT Bloodstream infection (BSI) due to multidrug-resistant Klebsiella is associated with high rates of morbidity and mortality. The aim of this study was to identify predictors of in-hospital mortality among patients with BSI due to ceftazidime-resistant (CAZ-R) Klebsiella pneumoniae at a tertiary care medical center. Patients with CAZ-R K. pneumoniae BSI were identified by our microbiology laboratory between January 1995 and June 2003. Clinical data were collected retrospectively. Logistic regression was used to identify independent predictors of all causes of in-hospital mortality. Of 779 patients with K. pneumoniae BSI, 60 (7.7%) had BSI due to CAZ-R K. pneumoniae; 43 (72%) of these were nosocomial infections. Pulsed-field gel electrophoresis identified a single predominant strain in 17 (28%) patients. The in-hospital mortality rate was 43% (n = 26). Among patients with CAZ-R K. pneumoniae BSI, those who died were similar to survivors with respect to demographic, clinical, and antimicrobial susceptibility characteristics. Only 43 (72%) patients received effective therapy within 5 days of BSI. In bivariable analysis, delay in initiation of effective therapy for >72 h after diagnosis of BSI was associated with death (P = 0.03). Strain genotype was not predictive of outcome. In multivariable analysis, delay in initiation of effective therapy for >72 h after diagnosis of BSI was an independent predictor of death (odds ratio, 3.32; 95% confidence interval, 1.07 to 10.3). Thus, among patients with BSI due to CAZ-R K. pneumoniae, a delay in the initiation of effective therapy of greater than 72 h after BSI was associated with a >3-fold increase in mortality risk.

Antibiotic Resistance in Urinary Isolates of Escherichia coli from College Women with Urinary Tract Infections

ABSTRACT Of 176 urine isolates from female students positive for Escherichia coli, 29.6% were trimethoprim-sulfamethoxazole resistant and none were nitrofurantoin resistant. Among students with a history of urinary tract infection (UTI) (n = 119), resistance to ciprofloxacin was 11.8%, compared to 1.8% among those without prior UTI. Nitrofurantoin should be considered for empirical therapy of lower tract UTI.

Sequential Emergence of Antibiotic Resistance in Enterococcal Bloodstream Isolates over 25 Years

ABSTRACT We determined the antibiotic susceptibilities of 1,785 enterococcal bloodstream isolates collected over 25 years. Antibiotic resistance emerged at a greater rate in Enterococcus faecium than in other enterococcal species, and E. faecium isolates became proportionally more common over time. Our findings confirm the pattern of emerging antibiotic resistance among enterococci and highlight the increasing importance of E. faecium as a cause of bloodstream infection.