(42 days)
The VITEK® 2 Antimicrobial Susceptibility Test (AST) is intended to be used with the VITEK® 2 and VITEK® 2 Compact Systems for the automated quantitative or qualitative susceptibility testing of most clinically significant aerobic gram-positive cocci such as Staphylococcus spp., Enterococcus spp., Streptococcus agalactiae, and S. pneumoniae. VITEK® 2 Gram Positive Meropenem is designed for antimicrobial susceptibility testing of Staphylococcus aureus and Staphylococcus epidermidis. VITEK 2 Gram Positive Meropenem is a qualitative tool. It 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 antimicrobial agents.
The VITEK 2 AST Cards are essentially miniaturized versions of the doubling dilution technique for determining the minimum inhibitory concentration (MIC) 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 Compact has a manual filling and sealing operation. The VITEK 2 systems monitor 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 along with the interpretive category result for each antibiotic contained on the card.
Here's a breakdown of the acceptance criteria and study details for the VITEK® 2 Gram Positive Meropenem as described in the provided 510(k) summary:
Acceptance Criteria and Device Performance Study
1. Table of Acceptance Criteria and Reported Device Performance
| Performance Metric | Acceptance Criteria (Implicit) | Reported Device Performance |
|---|---|---|
| Overall Category Agreement | Substantial equivalence to the NCCLS (now CLSI) reference agar dilution method. Specifically, high percentage agreement. | 100% Overall Category Agreement when compared to the agar dilution reference method. |
| Reproducibility | Acceptable results. | Demonstrated acceptable results. |
| Quality Control | Acceptable results. | Demonstrated acceptable results. |
Explanation of Acceptance Criteria: The primary acceptance criterion for this device, a Fully Automated Short-Term Incubation Cycle Antimicrobial Susceptibility Device, is "substantial equivalence" to a predicate device and a recognized reference method. For AST devices, this typically translates to high percentage agreement with the reference method across several categories: Essential Agreement (EA), Category Agreement (CA), and often minor, major, and very major error rates. While specific numeric acceptance thresholds for these error rates are not explicitly stated as "acceptance criteria" here, the 100% overall Category Agreement indicates that these thresholds were met implicitly, given the FDA clearance.
2. Sample Size Used for the Test Set and Data Provenance
- Sample Size for Test Set: Not explicitly stated as a single number. The study was conducted with "fresh and stock clinical isolates and stock challenge strains." The text notes that "external evaluations were designed to confirm the [performance] of VITEK 2 Gram Positive Meropenem by comparing its performance with the CLSI (NCCLS) agar dilution reference method." This implies a sufficiently large and diverse set of isolates was used to achieve the reported 100% agreement.
- Data Provenance: The study was an "external evaluation," which suggests controlled laboratory settings, likely in the US given the FDA submission. The terms "fresh and stock clinical isolates" indicate a mix of recently isolated clinical samples and established strains from laboratory collections. "Stock challenge strains" are typically well-characterized strains used for robust validation. The text does not explicitly state the country of origin of the clinical data but "external evaluation" for an FDA submission generally implies US-based data gathered specifically for regulatory purposes. It is a prospective study in the sense that the device's performance was evaluated against a reference method on these isolates for the purpose of this submission.
3. Number of Experts Used to Establish the Ground Truth for the Test Set and Their Qualifications
- Number of Experts: Not specified.
- Qualifications of Experts: Not specified. However, for a reference method like NCCLS/CLSI agar dilution, the ground truth would be established by trained microbiologists following standardized laboratory protocols. The method itself is the "gold standard" here, and the "experts" would be the personnel carrying out the reference testing accurately.
4. Adjudication Method for the Test Set
- Adjudication Method: Not applicable in the traditional sense of human consensus for image interpretation. The ground truth (reference method result) is established objectively by the agar dilution method, which produces a Minimum Inhibitory Concentration (MIC) value. The VITEK 2 result (MIC and interpretive category) is then compared directly to this reference MIC and category. Discrepancies would be resolved by retesting according to established microbiology laboratory procedures, not typically by an adjudication panel comparing interpretations.
5. Multi-Reader Multi-Case (MRMC) Comparative Effectiveness Study
- MRMC Study Done: No. This device is an automated antimicrobial susceptibility testing system, not an imaging device requiring human-in-the-loop interpretation. Therefore, a multi-reader multi-case comparative effectiveness study comparing human readers with and without AI assistance is not relevant to this type of device.
6. Standalone Performance Study
- Standalone Study Done: Yes. The entire study described is a standalone performance evaluation. The VITEK 2 Gram Positive Meropenem's performance (its ability to determine antimicrobial susceptibility) was directly compared to the NCCLS reference agar dilution method. This is a direct measure of the algorithm/device's accuracy without human intervention influencing the result generation. The device automatically performs the test and generates the interpretive category.
7. Type of Ground Truth Used
- Type of Ground Truth: The ground truth was established using the NCCLS (now CLSI) reference agar dilution method. This is considered the "gold standard" for determining Minimum Inhibitory Concentrations (MICs) and interpretive categories (Susceptible, Intermediate, Resistant) for antimicrobial agents.
8. Sample Size for the Training Set
- Sample Size for Training Set: Not explicitly stated. The document describes a performance evaluation (test set) but does not detail the size or nature of a separate training set. For an AST device like VITEK 2, development often involves extensive internal testing and optimization (which could be considered a form of "training" or development data) using a large library of characterized strains, before formal external validation is performed. The 510(k) summary focuses on the validation study demonstrating performance.
9. How the Ground Truth for the Training Set Was Established
- Ground Truth for Training Set: Not explicitly detailed. Similar to the test set, the ground truth for any development or "training" data for an AST device would typically be established using the CLSI/NCCLS reference methods (such as agar dilution or broth microdilution) to determine the true MICs and interpretive categories of the bacterial isolates used in development. This is a standard and robust method for establishing ground truth in microbiology.
§ 866.1645 Fully automated short-term incubation cycle antimicrobial susceptibility system.
(a)
Identification. A fully automated short-term incubation cycle antimicrobial susceptibility system is a device that incorporates concentrations of antimicrobial agents into a system for the purpose of determining in vitro susceptibility of bacterial pathogens isolated from clinical specimens. Test results obtained from short-term (less than 16 hours) incubation are used to determine the antimicrobial agent of choice to treat bacterial diseases.(b)
Classification. Class II (special controls). The special control for this device is FDA's guidance document entitled “Class II Special Controls Guidance Document: Antimicrobial Susceptibility Test (AST) Systems; Guidance for Industry and FDA.”