Clinical Evaluation and Cost Analysis of Great Basin Shiga Toxin Direct Molecular Assay for Detection of Shiga Toxin-Producing Escherichia coli in Diarrheal Stool Specimens.

The Shiga Toxin Direct molecular assay (ST Direct) relies on nucleic acid amplification and solid array-based amplicon detection to identify Shiga toxin-producing Escherichia coli (STEC) in preserved stool specimens. Genes encoding Shiga toxin (stx1 and stx2), as well as the E. coli serotype O:157-specific marker rfbE, are simultaneously detected within 2 h. ST Direct was evaluated using 1,084 prospectively collected preserved stool specimens across five clinical centers. An additional 55 retrospectively collected, frozen specimens were included to increase the number of positive specimens evaluated. Results were compared to results from routine culture and an enzyme immunoassay (EIA) specific for the recovery and identification of STEC. ST Direct was found to be 93.2% sensitive and 99.3% specific for detection of stx1 and stx2 and 95.7% sensitive and 99.3% specific for detection of E. coli serotype O:157. All specimens with false-positive results were found to contain stx1 or stx2 or were found to be positive for serotype O:157 when analyzed using alternative molecular methods. All 4 false-negative stx1 or stx2 results were reported for frozen, retrospectively tested specimens. In all cases, the specimens tested positive for stx by an alternative FDA-cleared nucleic acid amplification test (NAAT) but were negative for stx1 and stx2 following nucleic acid sequence analysis. Based on these data, culture and EIA-based methods for detection of STEC are only 33% sensitive compared to molecular tests. A retrospective cost analysis demonstrated 59% of the cost of routine stool culture to be attributable to the identification of STEC. Taken together, these data suggest that ST Direct may provide a cost-effective, rapid molecular alternative to routine culture for the identification of STEC in preserved stool specimens.

Automatic Digital Analysis of Chromogenic Media for Vancomycin-Resistant-Enterococcus Screens Using Copan WASPLab.

Vancomycin-resistant enterococci (VRE) are an important cause of health care-acquired infections (HAIs). Studies have shown that active surveillance of high-risk patients for VRE colonization can aid in reducing HAIs; however, these screens generate a significant cost to the laboratory and health care system. Digital imaging capable of differentiating negative and "nonnegative" chromogenic agar can reduce the labor cost of these screens and potentially improve patient care. In this study, we evaluated the performance of the WASPLab Chromogenic Detection Module (CDM) (Copan, Brescia, Italy) software to analyze VRE chromogenic agar and compared the results to technologist plate reading. Specimens collected at 3 laboratories were cultured using the WASPLab CDM and plated to each site's standard-of-care chromogenic media, which included Colorex VRE (BioMed Diagnostics, White City, OR) or Oxoid VRE (Oxoid, Basingstoke, United Kingdom). Digital images were scored using the CDM software after 24 or 40 h of growth, and all manual reading was performed using digital images on a high-definition (HD) monitor. In total, 104,730 specimens were enrolled and automation agreed with manual analysis for 90.1% of all specimens tested, with sensitivity and specificity of 100% and 89.5%, respectively. Automation results were discordant for 10,348 specimens, and all discordant images were reviewed by a laboratory supervisor or director. After a second review, 499 specimens were identified as representing missed positive cultures falsely called negative by the technologist, 1,616 were identified as containing borderline color results (negative result but with no package insert color visible), and 8,234 specimens were identified as containing colorimetric pigmentation due to residual matrix from the specimen or yeast (Candida). Overall, the CDM was accurate at identifying negative VRE plates, which comprised 84% (87,973) of the specimens in this study.

Resistance Mechanisms, Epidemiology, and Approaches to Screening for Vancomycin-Resistant Enterococcus in the Health Care Setting.

Infections attributable to vancomycin-resistant Enterococcus (VRE) strains have become increasingly prevalent over the past decade. Prompt identification of colonized patients combined with effective multifaceted infection control practices can reduce the transmission of VRE and aid in the prevention of hospital-acquired infections (HAIs). Increasingly, the clinical microbiology laboratory is being asked to support infection control efforts through the early identification of potential patient or environmental reservoirs. This review discusses the factors that contribute to the rise of VRE as an important health care-associated pathogen, the utility of laboratory screening and various infection control strategies, and the available laboratory methods to identify VRE in clinical specimens.

Detection of Group A Streptococcus in Pharyngeal Swab Specimens by Use of the AmpliVue GAS Isothermal Helicase-Dependent Amplification Assay.

We evaluated the clinical performance (sensitivity and specificity) of the AmpliVue group A Streptococcus (GAS) isothermal helicase-dependent amplification assay using 1,192 pharyngeal swab specimens. AmpliVue GAS assay results were compared to the results of routine throat cultures on selective streptococcal blood agar plates. The sensitivity and specificity of the AmpliVue GAS assay were 98.3% (95% confidence interval [CI], 95 to 100%) and 93.2% (95% CI, 91 to 95%), respectively.