(105 days)
VRESelect ™ is a selective and differential chromogenic medium, containing 8 µg/mL of vancomycin, for the qualitative detection of gastrointestinal colonization of vancomycin-resistant Enterococcus faecium (VREfm) and vancomycin-resistant Enterococcus faecalis (VREfs) and to aid in the prevention and control of vancomycin-resistant Enterococcus (VRE) in healthcare settings. The test is performed on rectal swabs or fecal specimens from patients to be screened for VRE colonization. VRESelect ™ is not intended to diagnose VRE infection nor to guide or monitor treatment of infection. Results can be interpreted after 24 to 28 hours incubation. Subculture to non-selective media (e.g., trypticase soy agar with 5% sheep blood) is needed for susceptibility testing and epidemiological typing.
VRESelect ™ is a selective medium for the detection of vancomycin-resistant Enterococcus (VRE). The selectivity of this medium is based on the presence of an antifungal/antibiotic mixture that inhibits the growth of most yeast, Gram negative and Gram positive bacteria, with the exception of vancomycin-resistant Enterococci (VRE).
Detection is based on the cleavage of chromogenic substrates by specific enzymes of Enterococcus faecium which produces pink colonies and Enterococcus faecalis which produces blue colonies.
Enterococcus gallinarum and Enterococcus casseliflavus are intrinsically resistant to vancomycin and may grow on the VRESelect™ medium as colorless or white colonies because they do not metabolize the chromogenic substrates. Vancomycin susceptible enterococci are inhibited.
After 24 to 28 hours incubation pink colonies can be reported as VREfm. Blue colonies should be confirmed by a catalase test and susceptibility (refer to limitation 9 in package insert).
K122187: VRESelect™ Media Acceptance Criteria and Performance Study
The VRESelect™ Media is a selective and differential chromogenic medium intended for the qualitative detection of gastrointestinal colonization of vancomycin-resistant Enterococcus faecium (VREfm) and Enterococcus faecalis (VREfs).
1. Acceptance Criteria and Reported Device Performance
The acceptance criteria for VRESelect™ Media are not explicitly stated as numerical thresholds in this document. However, performance is assessed through comparison with a predicate device (BEAV + Confirmation) and established laboratory methods (Biochemical identification (Vitek) and Vancomycin minimal inhibitory concentration (MIC) by E-Test). The implicit acceptance criteria appear to be high levels of positive and negative agreement with these reference methods.
| Metric | Acceptance Criteria (Implicit) | Reported Device Performance (24 hours) | Reported Device Performance (28 hours) |
|---|---|---|---|
| Method Comparison (vs. BEAV + Confirmation) | |||
| % Positive Agreement | High agreement | 96% (182/189, [0.92, 0.98]) | 98% (186/189, [0.95, 0.99]) |
| % Negative Agreement | High agreement | 96% (727/757, [0.94, 0.97]) | 95% (721/757, [0.93, 0.96]) |
| Biochemical Identification (vs. Vitek) | |||
| VREfm | |||
| % Positive Agreement | High agreement | 94% (171/181, [0.90, 0.97]) | 97% (175/181, [0.93, 0.99]) |
| % Negative Agreement | High agreement | 97% (740/765, [0.95, 0.98]) | 96% (734/765, [0.94, 0.97]) |
| VREfs | |||
| % Positive Agreement | High agreement | 94% (15/16, [0.70, 0.99]) | 94% (15/16, [0.70, 0.99]) |
| % Negative Agreement | High agreement | 98% (910/930, [0.97, 0.99]) | 98% (909/930, [0.97, 0.99]) |
| Vancomycin Resistance (vs. E-Test) | |||
| VREfm | |||
| % Positive Agreement | High agreement | 96% (171/178, [0.92, 0.98]) | 98% (175/178, [0.95, 0.99]) |
| % Negative Agreement | High agreement | 97% (743/768, [0.95, 0.98]) | 96% (737/768, [0.94, 0.97]) |
| VREfs | |||
| % Positive Agreement | High agreement | 100% (12/12, [0.82, 1.00]) | 100% (12/12, [0.82, 1.00]) |
| % Negative Agreement | High agreement | 98% (911/934, [0.96, 0.99]) | 97% (910/934, [0.96, 0.98]) |
The conclusion states that "The VRESelect™ showed high diagnostic sensitivity and accuracy in this study," indicating that the reported performance met the sponsor's internal acceptance criteria.
2. Sample Size and Data Provenance for the Test Set
- Sample Size: 946 stool samples were used for the method comparison study.
- Data Provenance: The document does not explicitly state the country of origin for the samples. It also doesn't specify if the samples were retrospective or prospective, though the nature of a method comparison study often implies prospectively collected samples or a mixed approach.
3. Number of Experts and Qualifications for Ground Truth for the Test Set
The document does not specify the number of individual experts involved in establishing the ground truth for the test set. However, it indicates these processes:
- For the Method Comparison Study (vs. BEAV + Confirmation): It states "confirmatory testing (Gram stain, catalase, PYR, Vitek 2 identification and vancomycin (MIC E-Test))." This implies established laboratory protocols and potentially certified laboratory personnel rather than individual "experts" in the sense of clinical specialists.
- For Biochemical identification (Vitek) and Vancomycin minimal inhibitory concentration (MIC) (E-Test): These are standard laboratory methods with established protocols.
No specific qualifications (e.g., "radiologist with 10 years of experience") are mentioned for these individuals, as the ground truth relies on recognized laboratory tests rather than expert interpretation of images or clinical findings.
4. Adjudication Method for the Test Set
The document does not describe an adjudication method in the context of multiple human readers or interpretations. The ground truth for the test set was established through a combination of a predicate device (BEAV) and a series of confirmatory laboratory tests (Gram stain, catalase, PYR, Vitek 2 identification, and vancomycin (MIC E-Test)). These are objective laboratory procedures, which typically do not involve an "adjudication" process in the same way clinical interpretations might.
5. Multi-Reader Multi-Case (MRMC) Comparative Effectiveness Study
No, an MRMC comparative effectiveness study was not performed. The study evaluates the performance of the VRESelect™ medium itself against established laboratory methods, not how human readers improve with or without AI assistance. The device is a culture medium, not an AI or human-assisted diagnostic tool in the typical sense of an MRMC study.
6. Standalone Performance Study
Yes, a standalone performance study was done. The entire document describes the performance of the VRESelect™ media (the algorithm/device only, without human interpretation beyond reading the colonies) against established ground truth methods. The results are presented as agreement percentages.
7. Type of Ground Truth Used
The ground truth used was a combination of:
- Predicate Device Performance: The results from the current standard, "BEAV plus Confirmation."
- Laboratory Diagnostic Tests: This includes Gram stain, catalase, PYR, Vitek 2 identification, and vancomycin (MIC E-Test) for bacterial identification and resistance determination. This aligns with what can be considered definitive laboratory methods/gold standard diagnostic tests.
8. Sample Size for the Training Set
The document does not explicitly mention a separate "training set" or "training data" in the context of machine learning model development. This is because VRESelect™ is a chromogenic culture medium, not an AI/machine learning algorithm that requires training. Its performance is based on biochemical reactions and enzymatic activity, which are inherent properties of the medium. The studies described are validation or verification studies, not training for an adaptive algorithm.
However, if we interpret "training" in a broader sense of product development and optimization, the "limit of detection study" involving a panel of 18 vancomycin-resistant enterococci and the "challenge panel" of 56 well-characterized strains could be considered part of the development and refinement process, though not a "training set" for a learning algorithm.
9. How the Ground Truth for the Training Set (if applicable) was Established
As noted above, there is no explicit "training set" as understood in machine learning. For the studies that involved characterized strains (e.g., Limit of Detection, Challenge Panel), the ground truth for these strains would have been established through well-defined microbiological methods, including identification to species level and vancomycin susceptibility testing using standard laboratory techniques (e.g., AST methods like MIC E-Test or broth microdilution). The "ATCC reference strains" mentioned in the reproducibility study also serve as a form of "ground truth" with known characteristics.
§ 866.1700 Culture medium for antimicrobial susceptibility tests.
(a)
Identification. A culture medium for antimicrobial susceptibility tests is a device intended for medical purposes that consists of any medium capable of supporting the growth of many of the bacterial pathogens that are subject to antimicrobial susceptibility tests. The medium should be free of components known to be antagonistic to the common agents for which susceptibility tests are performed in the treatment of disease.(b)
Classification. Class II (performance standards).