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VITEK 2 AST-Yeast Anidulafungin is designed for antifungal susceptibility testing of Candida species and is intended for use with the VITEK 2 and VITEK 2 Compact Systems as a laboratory aid in the determination of in vitro susceptibility to antifungal agents. VITEK 2 AST-Yeast Anidulafungin is a quantitative test. Anidulafungin has been shown to be active against most strains of the microorganisms listed below, according to the FDA label for this antifungal.

Active in vitro and in clinical infections: Candida albicans Candida glabrata Candida parapsilosis Candida tropicalis

In vitro data are available, but clinical significance is unknown: Candida guillermondii Candida krusei

The VITEK 2 Fungal Susceptibility Card is intended for use with the VITEK 2 Systems in clinical laboratories as an in vitro test to determine the susceptibility of clinically significant yeasts to antifungal agents when used as instructed.

The principle of the VITEK® 2 AST cards is based on the microdilution minimum inhibitory concentration (MIC) technique reported by MacLowry and Marsh (1) and Gerlach(2). The VITEK® 2 AST card is essentially a miniaturized, abbreviated and automated version of the doubling dilution technique (3).

Each VITEK® 2 AST card contains 64 wells. A control well which only contains microbiological culture media is resident on all cards. The remaining wells contain premeasured portions of a specific antibiotic combined with culture media. The bacterial or yeast isolate to be tested is diluted to a standardized concentration with 0.45 – 0.5% saline before being used to rehydrate the antimicrobial medium within the card. The VITEK® 2 System automatically fills, seals and places the card into the incubator/reader. The VITEK® 2 Compact has a manual filling, sealing and loading operation. The VITEK® 2 Systems monitor the growth of each well in the card over a defined period of time. At the completion of the incubation cycle, a report is generated that contains the MIC value along with the interpretive category result for each antibiotic contained on the card.

VITEK® 2 AST-YS Anidulafungin has the following concentrations in the card: 0.0625, 0.125, 0.5, 2, and 8 (equivalent standard method concentration by efficacy in ug/mL).

Here's an analysis of the acceptance criteria and the study proving the device meets those criteria, based on the provided text.

Device: VITEK 2 AST-Yeast Anidulafungin

Indications for Use: Antifungal susceptibility testing of Candida species (C. albicans, C. glabrata, C. parapsilosis, C. tropicalis, C. guilliermondii, C. krusei) as a laboratory aid in determining in vitro susceptibility to antifungal agents.

1. Table of Acceptance Criteria and Reported Device Performance

The provided document doesn't explicitly state the acceptance criteria in a separate table directly defining thresholds for Essential Agreement (EA), Category Agreement (CA), or error rates (VME, ME, mE) that the device must meet for approval. Instead, it presents the results of the performance study and implies that these results were deemed "acceptable" by the FDA. The performance is compared to the "CLSI broth microdilution reference method, as defined in the FDA Class II Special Controls Guidance Document: Antimicrobial Susceptibility Test (AST) Systems; Guidance for Industry and FDA (Issued August 28, 2009)". This guidance document would contain the specific acceptance criteria.

However, based on the presented "Performance Overview" (Page 7) and the overall context of AST device approvals, typical acceptance criteria for Essential Agreement and Category Agreement are usually in the range of 90-95% or higher, with Very Major Error (VME) and Major Error (ME) rates usually being low (e.g., <3% or <1.5%).

Here's the reported device performance:

Note on C. tropicalis VME: The document specifically highlights: "When evaluating VITEK 2 AST-YS Anidulafungin, there was a single very major error (VMJ) that resulted in an unacceptable VMJ rate of 33.3% (1/3) with C. tropicalis." Despite this, the overall conclusion states "VITEK® 2 AST-YS Anidulafungin demonstrated acceptable performance." This suggests that either the unacceptably high VME for C. tropicalis was mitigated by other factors (e.g., small sample size for VME calculation, or specific post-market surveillance requirements), or it points to a known limitation that the FDA found acceptable for clearance under the stated conditions.

2. Sample Size Used for the Test Set and Data Provenance

• Sample Size for Test Set:

  • C. albicans: 206 isolates
  • C. glabrata: 116 isolates
  • C. guilliermondii: 21 isolates
  • C. krusei: 69 isolates
  • C. parapsilosis: 72 isolates
  • C. tropicalis: 81 isolates
  • Total Isolates: 565 isolates across the specified Candida species.

• Data Provenance: The study involved an "external evaluation" conducted with "fresh and stock clinical isolates, as well as a set of challenge strains." The document does not specify the country of origin of the data or whether it was retrospective or prospective. Typically, "clinical isolates" imply prospective collection from real patient samples, and "stock isolates" could be reference strains or previously collected clinical isolates. "External evaluation" implies data was collected from multiple sites, which is standard for clinical trials of this nature.

3. Number of Experts Used to Establish Ground Truth for the Test Set and Their Qualifications

This information is not provided in the document. For antimicrobial susceptibility testing (AST) devices, the ground truth is established by a reference method (here, the CLSI broth microdilution reference method), not by human expert interpretation of images or data in a consensus setting.

4. Adjudication Method for the Test Set

Not applicable. The ground truth for AST devices is established by a standardized laboratory reference method (CLSI broth microdilution), not through expert adjudication of ambiguous cases like in imaging studies.

5. If a Multi-Reader Multi-Case (MRMC) Comparative Effectiveness Study Was Done

No, an MRMC comparative effectiveness study was not performed. This type of study (comparing human readers with and without AI assistance on diagnostic tasks) is not relevant for an automated antimicrobial susceptibility testing device like the VITEK 2 AST-Yeast Anidulafungin. This device provides quantitative MIC values and interpretive categories, not an interpretation of a medical image or clinical data that would involve human readers.

6. If a Standalone (i.e., Algorithm Only Without Human-in-the-Loop Performance) Was Done

Yes, the performance study effectively evaluates the standalone performance of the VITEK 2 AST-Yeast Anidulafungin system. The device automatically reads and interprets the growth patterns in the microdilution wells to generate MIC values and interpretive categories (Susceptible, Intermediate, Resistant). This automated result is then compared directly to the established ground truth (CLSI broth microdilution reference method). While human operators physically load the cards, the core performance being evaluated is the device's automated analysis.

7. The Type of Ground Truth Used

The type of ground truth used was the CLSI broth microdilution reference method (Clinical and Laboratory Standards Institute). This is a well-established, standardized, and validated laboratory method for determining the minimum inhibitory concentration (MIC) of an antimicrobial agent against a microorganism. The reference method results serve as the "gold standard" for accuracy in AST device performance studies.

8. The Sample Size for the Training Set

The document does not provide specific details about the training set size. The device uses "Discriminant Analysis" algorithms. Typically, for a device like this, the algorithms would be developed and refined using a large dataset of isolates with known reference MICs to optimize the mapping between the device's optical measurements and the true MICs. However, the exact size of this internal development/training set is not disclosed in this summary. The provided performance data (the "test set") is for validation purposes, distinct from the training set.

9. How the Ground Truth for the Training Set Was Established

While not explicitly stated for a "training set" in this document, it is highly probable that the ground truth for any isolates used during the development and training of the VITEK 2 system's algorithms would also have been established using the CLSI broth microdilution reference method or similar highly standardized and validated laboratory methods, consistent with industry best practices for AST device development. This ensures that the algorithm learns from accurate data.

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