The first U.S. multicenter clinical trial to assess the performance of the Cepheid Xpert MRSA assay (Xpert MRSA) was conducted. The assay is a qualitative test designed for the rapid detection of methicillin-resistant Staphylococcus aureus (MRSA) directly from nares swabs. This novel test combines integrated nucleic acid extraction and automated real-time PCR for the detection of a MRSA-specific signature sequence. A total of 1,077 nares specimens were collected from seven geographically distinct health care sites across the United States with prevalence rates ranging from 5.2% to 44%. Nares specimens were tested by (i) the Xpert MRSA assay, (ii) direct culture on CHROMagar MRSA medium (direct CM culture), and (iii) broth-enriched culture (Trypticase soy broth with 6.5% sodium chloride) followed by plating onto CHROMagar MRSA medium (broth-enriched CM culture). When direct CM culture was designated the reference method, the sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of the Xpert MRSA assay were 94.3%, 93.2%, 73.0%, and 98.8%, respectively. When broth-enriched CM culture was used as the reference method, the clinical sensitivity, specificity, PPV, and NPV of the Xpert MRSA assay were 86.3%, 94.9%, 80.5%, and 96.6%, respectively. The BD GeneOhm MRSA (BDGO) assay was performed as a comparative molecular method. No statistical performance differences were observed between the Xpert MRSA and BDGO assays when they were compared to culture methods. From this large-scale, multicenter clinical comparison, we conclude that the Xpert MRSA assay is a simple, rapid, and accurate method for performing active surveillance for MRSA in a variety of health care populations.

Clostridium difficile infection (CDI) is changing as evidenced by increasing virulence, rising incidence, unresponsiveness to metronidazole therapy, and worse outcomes. Thus, it is critical that CDI diagnosis be accurate so ongoing epidemiology, disease prevention, and treatment remain satisfactory. We tested 10 diagnostic assays, including 1 commercial real-time polymerase chain reaction (qPCR) test for the laboratory detection of toxigenic C difficile on 1,000 stool samples. Sensitive culture for toxigenic C difficile using 2 types of media with broth enrichment defined the reference standard. For the study, 1,000 tests were performed on samples from 919 patients. Of the samples, 146 contained evidence for toxigenic C difficile and represented the true-positive results. Only the US Food and Drug Administration-cleared qPCR assay (Becton Dickinson, Franklin Lakes, NJ) and 1 glutamate dehydrogenase test (TechLab, Blacksburg, VA) were not statistically inferior to culture in sensitivity. The common enzyme immunoassay tests all had sensitivity values less than 50%. Clinical laboratory professionals need to seriously consider their diagnostic testing and use the assays that perform best for the detection of CDI.

The rate of methicillin-resistant Staphylococcus aureus (MRSA) infection continues to rise in many health care settings. Rapid detection of MRSA colonization followed by appropriate isolation can reduce transmission and infection. We compared the performance of the new Roche LightCycler MRSA advanced test to that of the BD GeneOhm MRSA test and culture. Double-headed swabs were used to collect anterior nasal specimens from each subject.

Surveillance for methicillin-resistant Staphylococcus aureus (MRSA) colonization can be an important element for infection control programs when managing a multidrug-resistant pathogen such as MRSA. The sensitivity and speed of laboratory testing affects the proportion of appropriate isolation days captured, which determines the success or failure of a MRSA control program. Chromogenic culture, CHROMagar MRSA (BBL, Becton Dickinson, Sparks, MD) and MRSASelect (Bio-Rad, Hercules, CA), with and without broth enrichment and real-time polymerase chain reaction (PCR; BD GeneOhm MRSA, BD Diagnostics, San Diego, CA), were compared and found to have a wide range of sensitivities (78.5%-98.2%), specificities (91.6%-100.0%), and turnaround times (2-72 hours). Real-time PCR provided the most rapid results and demonstrated the highest sensitivity followed by broth-enriched culture and then direct plating for MRSA detection in nasal swabs. There was no substantial difference in the labor required for any of the 3 approaches.

The BD GeneOhm VanR assay (BD Diagnostics, San Diego, CA), a qualitative test for the rapid detection of vancomycin-resistant enterococci (VRE) from rectal and/or perianal swabs, combines integrated nucleic acid extraction and automated polymerase chain reaction for the detection of vanA and/or vanB gene sequences. We studied 1,027 perianal and rectal swab specimens from 3 geographically distinct US sites (prevalence rates, 13.1%-25.8%). Direct swab specimens were tested by the assay and compared with direct culture. The sensitivity, specificity, and positive and negative predictive values of the assay were 93.2%, 81.9%, 54.4%, and 98.1%, respectively. The specificity was limited largely due to false-positives in the vanB portion of the assay. Specificity with perianal swabs was significantly greater than with rectal swabs, 87.1% vs 74.7%, respectively (P < .0001). When used only to detect resistance conferred by vanA, the assay was 88.3% (158/179) sensitive and 95.8% (802/837) specific, with positive and negative predictive values of 81.9% and 97.4%, respectively. The assay is a simple, rapid, and acceptable method for screening for VRE in a variety of populations in which vanA is the predominant genotype. Samples positive for the vanB genotype should be confirmed by culture owing to the apparent high number of false-positive results.

We compared two real-time PCR assays (both by the use of melting curve analysis) for their ability to identify Staphylococcus species directly from 200 positive blood culture bottles. The PCR assays correctly identified 83% to 94% of the Staphylococcus isolates to species clusters. Molecular testing significantly outperformed commercially available latex tests (sensitivity for both latex tests, <15%) when it was used directly with broth from signal-positive blood cultures.

The ten-dose regimen is superior to any six-dose regimen for de-colonizing S. aureus from the anterior nares of patients and for maintaining the decolonized state for at least four weeks after therapy.

Nasal and perianal swab specimens were tested for detection of Staphylococcus aureus and vancomycinresistant Enterococcus species (VRE) using a laboratory-developed real-time PCR test and microbiological cultures. The real-time PCR and culture results for S. aureus were similar. PCR had adequate sensitivity, but culture was more specific for the detection of VRE.Staphylococcus aureus, especially methicillin-resistant S. aureus (MRSA), and vancomycin-resistant Enterococcus species (VRE) are important pathogens associated with health care facility outbreaks worldwide (1,2,8,21). It has been reported that identifying asymptomatically colonized individuals and placing them into contact isolation within a short time frame are a good management tool for reducing the spread of these pathogens and for lowering health care-associated infections (5,11,16,18). Furthermore, there is rising interest in identifying all S. aureus carriers prior to surgery to decolonize them to reduce postoperative S. aureus surgical-site infections (4, 10).Reliable surveillance requires accurate testing (17), and cultures can take from 2 to 5 days to obtain the final results (3a). PCR offers detection of S. aureus and VRE directly from swab specimens within a few hours (4,12,14) and can help with the rapid deployment of infection control and prevention measures (16,18).The purpose of our study was to develop an optimized test using Roche analyte-specific reagents (ASRs) for detection of S. aureus and VRE by real-time PCR with a single set of amplification conditions and to compare the PCR results to the results of conventional culture.Inpatients at Evanston Northwestern Healthcare during August 2004 made up the patient population. Premoistened, double-headed swabs (culture swab; BBL, Becton Dickinson, Franklin Lakes, NJ) were used to collect paired anterior nasal specimens and paired perianal specimens as part of an infection control activity to determine colonization prevalence. There were 387 nasal specimens (for S. aureus) and 309 perianal specimens (for VRE). This investigation was approved by the Institutional Review Board of Evanston Northwestern Healthcare.For S. aureus, one of the paired nasal swabs was plated onto Columbia colistin-nalidixic agar with 5% sheep blood (Remel, Inc., Lenexa, KS) (3a) and incubated at 35°C for 48 h. S. aureus was identified by colony morphology and Staphaurex latex agglutination testing (Remel, Inc.). Methicillin resistance was determined on colonies by using PCR as described below. For any swabs that were PCR positive only for S. aureus (n ϭ 13), the original cultures were reexamined beyond their initial 48-hour incubation, with five additional swab samples yielding S. aureus after reexamination (two yielded MRSA).VRE was cultured by plating one of the paired perianal swabs on bile esculin azide agar containing 6 g of vancomycin/ml agar (Remel, Inc.) and by incubation at 35°C for 72 h. Colonies black in color (bile esculin positive) were confirmed to be Enterococcus faecium or Enterococcus faecalis by usi...