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VITEK® 2 Gram Positive Linezolid is designed for antimicrobial susceptibility testing of Enterococcus faecalis, E. faecium, Staphylococcus aureus, S. epidermidis, S. haemolyticus and Streptococcus agalactiae. It is intended for use with the VITEK® 2 System as a laboratory aid in the determination of in vitro susceptibility to antimicrobial agents.

The VITEK 2 AST Cards are essentially miniaturized versions of the doubling dilution technique for determining the minimum inhibitory concentration (MIC) my microdilution methodology. The bacterial isolate to be tested is diluted to a standardized concentration in 0.45% saline before being used to rehydrate the antimicrobial medium within the card. The VITEK 2 automatically fills, seals and places the card into the incubator/reader. The VITEK 2 monitors the growth of each well in the card over a defined period of time (up to 18 hours). 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.

The VITEK 2 Gram Positive Linezolid device's acceptance criterion for performance is defined as 98.7% overall Essential Agreement when compared to the NCCLS microbroth dilution reference method.

The study proving the device meets this criterion is an external evaluation conducted with fresh and stock clinical isolates and stock challenge strains.

Here's the detailed information requested:

1. Table of Acceptance Criteria and Reported Device Performance

2. Sample size used for the test set and the data provenance

• Sample Size for Test Set: The document states that an "external evaluation was conducted with fresh and stock clinical isolates and stock challenge strains." However, the exact number of isolates or strains used in this test set is not specified within the provided text.
• Data Provenance: The data is described as from "fresh and stock clinical isolates and stock challenge strains," indicating a prospective and retrospective mix for the clinical isolates, and prospective for stock challenge strains. The country of origin is not specified.

3. Number of experts used to establish the ground truth for the test set and the qualifications of those experts

• The document does not specify the number of experts or their qualifications. The ground truth method used is the NCCLS microbroth dilution reference method, which is a standardized laboratory procedure, not typically relying on expert interpretation in the same way, for example, a medical imaging diagnosis would.

4. Adjudication method for the test set

• None specified. The ground truth is established by the NCCLS microbroth dilution reference method, which is a standardized laboratory method, not typically requiring an adjudication process for its results.

5. If a multi-reader multi-case (MRMC) comparative effectiveness study was done, If so, what was the effect size of how much human readers improve with AI vs without AI assistance

• No. This device is an automated antimicrobial susceptibility testing system, not an AI-assisted diagnostic tool that involves human readers interpreting results in the way an MRMC study would evaluate. Therefore, this type of study was not performed, and there is no mention of improvement in human reader performance with AI assistance.

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

• Yes. The VITEK 2 system is a "Fully Automated Short-Term Incubation Cycle Antimicrobial Susceptibility Device." The performance evaluation compares the device's results directly to a reference method, which inherently describes its standalone, algorithm-only performance. The "human-in-the-loop" would be the initial preparation of the isolate and loading the card, but the interpretation and MIC determination are automated by the device.

7. The type of ground truth used

• The ground truth used is the NCCLS microbroth dilution reference method. This is a laboratory-based, standardized methodology for determining minimum inhibitory concentrations (MICs) of antimicrobial agents. It is considered the gold standard for antimicrobial susceptibility testing.

8. The sample size for the training set

• The document does not explicitly state a sample size for a training set. The described study is an "external evaluation" for performance confirmation. For a device incorporating a proprietary algorithm, training data would typically be used during development, but this information is not provided in the 510(k) summary.

9. How the ground truth for the training set was established

• As the training set sample size is not specified, the method for establishing its ground truth is also not described in the provided text. If a training set were used, it would likely also rely on the NCCLS microbroth dilution reference method or similar standardized laboratory methods to establish ground truth for MIC values.

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VITEK 2® Gram Positive Linezolid for Streptococcus pneumoniae is designed for antimicrobial susceptibility testing of Streptococcus pneumoniae. It is intended for use with the VITEK 2® System as a laboratory aid in the determination of in vitro susceptibility to antimicrobial agents.

The VITEK 2 AST Cards are essentially miniaturized versions of the doubling dilution technique for determining the minimum inhibitory concentration (MIC) my microdilution methodology. The bacterial isolate to be tested is diluted to a standardized concentration in 0.45% saline before being used to rehydrate the antimicrobial medium within the card. The VITEK 2 automatically fills, seals and places the card into the incubator/reader. The VITEK 2 monitors the growth of each well in the card over a defined period of time (up to 18 hours). 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.

The VITEK 2® Gram Positive Linezolid for Streptococcus pneumoniae device is designed for antimicrobial susceptibility testing of Streptococcus pneumoniae. It is intended for use with the VITEK 2® System as a laboratory aid in determining in vitro susceptibility to antimicrobial agents.

1. A table of acceptance criteria and the reported device performance

The acceptance criteria for this device are not explicitly quantified in the provided text in terms of specific percentages for Category Agreement, Essential Agreement, or Minor/Major/Very Major errors. However, the FDA's "Guidance on Review Criteria for Assessment of Antimicrobial susceptibility Devices" (March 8, 2000) and "Class II Special Controls Guidance Document: Antimicrobial Susceptibility Test (AST) Systems" (Feb 5, 2003) would have defined these criteria.

Based on the study results, the device demonstrated acceptable performance:

2. Sample size used for the test set and the data provenance

• Sample Size for Test Set: The document mentions "fresh and stock clinical isolates and stock challenge strains" for the external evaluation. However, the specific number of isolates used in the test set is not provided in the given text.
• Data Provenance: The data was obtained from an "external evaluation." The country of origin of the data is not specified, but given the submitter's address (Hazelwood, MO, USA) and the FDA approval process, it is highly likely tests were conducted or overseen within the USA. The data appears to be prospective as it's an evaluation conducted for regulatory submission.

3. Number of experts used to establish the ground truth for the test set and the qualifications of those experts

The ground truth was established using the NCCLS reference microbroth dilution method. This is a standardized laboratory method, not reliant on individual expert interpretation in the same way as, for example, a radiologist reading an image. Therefore, there were no human experts (like radiologists) establishing the ground truth; instead, it was a standardized biochemical assay result.

4. Adjudication method for the test set

The ground truth was established by the NCCLS reference microbroth dilution method. This method inherently provides a definitive result, so there was no adjudication method (e.g., 2+1, 3+1) needed among human experts, as the reference method served as the objective gold standard.

5. If a multi reader multi case (MRMC) comparative effectiveness study was done, If so, what was the effect size of how much human readers improve with AI vs without AI assistance

No, a multi-reader multi-case (MRMC) comparative effectiveness study involving human readers and AI assistance was not done. This device is an automated in vitro diagnostic device for antimicrobial susceptibility testing, not an imaging or interpretive AI system intended to assist human readers. It directly generates an MIC value and interpretive category.

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

Yes, this was a standalone performance study. The VITEK 2® system, on its own (algorithm and instrument), generated the susceptibility results which were then directly compared against the NCCLS reference method. There is no human-in-the-loop for the interpretation step of the VITEK 2 system's output that is described.

7. The type of ground truth used (expert consensus, pathology, outcomes data, etc.)

The type of ground truth used was the NCCLS reference microbroth dilution method. This is a standardized laboratory reference method for determining Minimum Inhibitory Concentrations (MICs).

8. The sample size for the training set

The document does not specify a separate "training set" or its sample size. The description focuses on an "external evaluation" as a test set. For an in vitro diagnostic device like this, the "training" (development and refinement) of the system likely involved internal testing and optimization by the manufacturer, but these details are not provided in the 510(k) summary.

9. How the ground truth for the training set was established

Since a "training set" is not explicitly mentioned or detailed, the method for establishing its ground truth is not provided. If an internal training set was used during development, it would also likely have been established using a similar reference method to the NCCLS microbroth dilution method for consistency and accuracy.

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