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VITEK® 2 AST-Yeast Caspofungin 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 Caspofungin is a quantitative test. Caspofungin 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 guilliermondii
Candida krusei
Candida parapsilosis
Candida tropicalis

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 Caspofungin has the following concentrations in the card: 0.125, 0.5, 2, and 8 (equivalent standard method concentration by efficacy in ug/mL).

The VITEK 2 AST-Yeast Caspofungin device is designed for antifungal susceptibility testing of Candida species. The study provided demonstrates its performance against the CLSI broth microdilution reference method.

Here's a breakdown of the information requested:

1. Table of Acceptance Criteria and Reported Device Performance

Note: The document doesn't explicitly state numerical acceptance criteria for EA, CA, VME, ME, and mE. The reported values are compared against what is generally considered acceptable in the field of antimicrobial susceptibility testing, often guided by FDA Class II Special Controls Guidance Document for AST Systems. The comment regarding VME indicates that despite the 100% (2/2) reported, the detailed analysis for specific Candida species outlines individual VMEs, suggesting these were analyzed within broader acceptability limits.

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

• Sample Size for Test Set: The number of isolates tested is derived from the agreement percentages.
  • Essential Agreement: 680 (Denominator for 679/680)
  • Category Agreement: 680 (Denominator for 663/680)
  • This indicates a total of 680 isolates were used in the external evaluation.
• Data Provenance: The external evaluation was conducted with:
  • "fresh and stock clinical isolates"
  • "a set of challenge strains"
  • Country of Origin: Not specified in the provided text.
  • Retrospective or Prospective: Not explicitly stated, however, the use of "fresh and stock clinical isolates" suggests a mix of potentially both, but the term "external evaluation" often implies collecting new data for the evaluation.

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

This type of device (Antimicrobial Susceptibility Test System) does not typically rely on human expert interpretation for establishing ground truth in the same way an imaging AI device would. Instead, the ground truth is established by a reference laboratory method.

• Ground Truth Method: CLSI broth microdilution reference method, incubated at 24 hours (or up to 48 hours for isolates with insufficient growth).
• Therefore, the concept of "experts" to establish ground truth with qualifications like "radiologist with 10 years of experience" is not applicable here. The ground truth accuracy relies on the validated performance of the CLSI method itself.

4. Adjudication Method for the Test Set

Not applicable. As the ground truth is established by a standardized laboratory reference method (CLSI broth microdilution), there is no human adjudication process involved in comparing different interpretations. The device's result is directly compared to the reference method result.

5. If a Multi-Reader Multi-Case (MRMC) Comparative Effectiveness Study was done

No, an MRMC comparative effectiveness study was not done. This type of study is relevant for diagnostic devices where human readers interpret data, often with and without AI assistance. The VITEK 2 is an automated system for measuring antimicrobial susceptibility and does not involve human readers interpreting results in the same context.

6. If a Standalone (i.e., algorithm only without human-in-the-loop performance) was done

Yes, the performance study conducted for the VITEK 2 AST-Yeast Caspofungin is a standalone performance study. The device, an automated system, generates results directly which are then compared to the reference method without human intervention in the device's determination process for the purpose of the study.

7. The Type of Ground Truth Used

The ground truth used was the CLSI broth microdilution reference method. This is a well-established and standardized laboratory method for determining the minimum inhibitory concentration (MIC) of antifungal agents against microorganisms.

8. The Sample Size for the Training Set

The document does not provide information on the sample size for the training set. This is typical for an AST system such as VITEK 2, where the underlying "algorithm" (discriminant analysis) is based on established principles of microbial growth detection and concentration determination, rather than a machine learning model that requires explicit "training data" in the common AI sense. The development of such systems often involves internal validation and optimization data that are not typically disclosed as a "training set" in regulatory summaries.

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

Given that explicit "training data" and "training set ground truth" are not mentioned, it can be inferred that the fundamental principles and thresholds used by the VITEK 2 system are based on:

• Established microbiological methods for microdilution (e.g., MacLowry and Marsh, Gerlach references provided).
• Optimization and validation using a variety of isolates during product development.
• Correlation with established breakpoints and guidelines from organizations like CLSI and FDA, which are derived from extensive expert analysis, clinical outcomes data, and epidemiological cut-off values.

Therefore, the ground truth for any hypothetical "training" or development phase would likely have been established using reference laboratory methods (similar to the CLSI broth microdilution used for the test set) in conjunction with expert consensus on interpretive breakpoints.

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