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VITEK® 2 AST-Streptococcus Cefotaxime is designed for antimicrobial susceptibility testing of Streptococcus spp. 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 antimicrobial agents. VITEK® 2 AST- Streptococcus Cefotaxime is a quantitative test. Cefotaxime has been shown to be active against most strains of the microorganisms listed below, according to the FDA label for this antimicrobial.

Active in vitro and in clinical infections:
Streptococcus pneumoniae
Streptococcus pyogenes (Group A beta-hemolytic streptococci)*
Streptococcus spp. (Viridans group streptococci)

*The VITEK® 2 Streptococus Susceptibility Card also reports the susceptibility of the following additional organisms as listed on the FDA Susceptibility Test Interia website (STIC): Streptococcus spp. B-Hemolytic Group (other than S. pyogenes).

The VITEK® 2 Streptococcus Susceptibility Card is intended for use with the VITEK® 2 Systems in clinical laboratories as an in vitro test to determine the susceptibility of S. pneumoniae, beta-hemolytic Streptococcus, and Viridans Streptococcus to antimicrobial 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(0). 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 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.

Here's an analysis of the acceptance criteria and the study proving the device meets them, based on the provided FDA 510(k) summary for VITEK® 2 AST-Streptococcus Cefotaxime:

1. Table of Acceptance Criteria and Reported Device Performance:

The document references "FDA Class II Special Controls Guidance Document: Antimicrobial Susceptibility Test (AST) Systems; Guidance for Industry and FDA (Issued August 28, 2009)" for defining acceptable performance. While the specific numerical acceptance criteria from this guidance are not explicitly called out in the provided text, the reported performance (Table 2) implicitly indicates that these criteria were met for the device to be deemed substantially equivalent. The table below presents the reported performance directly from the document.

Note on Acceptance Criteria: While not explicitly stated, FDA guidance for AST systems typically requires:

• Essential Agreement (EA): Generally ≥ 90%
• Category Agreement (CA): Generally ≥ 90%
• Major Error (ME) Rate: Generally ≤ 3%
• Very Major Error (VME) Rate: Generally ≤ 1.5%

Based on the reported performance, the device appears to meet these implied criteria. However, there's a specific note for Streptococcus pneumoniae (both meningitis and non-meningitis) where Minor Error (mE) is 10.0%, which is higher than typical acceptance for mE. For Streptococcus spp. Viridans Group, the EA is 97.3% and CA is 97.1%.

A note states: "The VITEK 2 Cefotaxime MIC values for Streptococcus spp Viridans Group tended to be at least one dilution lower than the reference method and may contribute to the occurrence of very major errors." However, the reported VME for this group is 0.0%.

2. Sample Size and Data Provenance:

The study involved an "external evaluation" with various types of isolates.

• Test Set Sample Sizes (from Table 2):
  • Streptococcus pneumoniae (meningitis): 351 isolates
  • Streptococcus pneumoniae (non-meningitis): 351 isolates
  • Streptococcus pyogenes (Group A β-Hemolytic Group) NS: 310 isolates
  • Streptococcus spp. β-Hemolytic Group (other than S. pyogenes) NS: 554 isolates
  • Streptococcus spp. Viridans Group: 408 isolates
• Data Provenance: The document states the external evaluation was "conducted with contemporary and stock clinical isolates, as well as a set of challenge strains." This suggests a mix of prospective (contemporary clinical isolates) and retrospective (stock clinical isolates and challenge strains) data. There is no explicit mention of the country of origin of the data.

3. Number of Experts and Qualifications for Ground Truth:

This information is not provided in the document. The ground truth (reference method) for the test set was established by the CLSI broth microdilution reference method; however, the involvement and qualifications of human experts in interpreting or reviewing these results are not detailed.

4. Adjudication Method for the Test Set:

This information is not provided in the document. For AST systems, the ground truth is typically the CLSI broth microdilution, which is a standardized laboratory procedure, so traditional adjudication methods like "2+1" or "3+1" used in imaging studies between human readers are not directly applicable here. The comparison is between the device's output and the reference method's output.

5. Multi-Reader Multi-Case (MRMC) Comparative Effectiveness Study:

No, an MRMC comparative effectiveness study was not done. This device is an automated antimicrobial susceptibility test system, meaning it directly outputs results (MIC values and interpretive categories). It does not involve human readers interpreting images or data that would then be compared with and without AI assistance. The performance comparison is solely between the automated system and a laboratory reference method.

6. Standalone (Algorithm Only) Performance:

Yes, a standalone performance evaluation was done. The entire study describes the performance of the VITEK® 2 AST-Streptococcus Cefotaxime system (which includes the algorithm for analysis) against the CLSI broth microdilution reference method. There is no human element in the interpretation of the VITEK® 2 system's results for this evaluation; it's the device's output being compared directly.

7. Type of Ground Truth Used:

The ground truth used was the CLSI broth microdilution reference method, which is a standardized laboratory procedure considered the gold standard for determining antimicrobial susceptibility.

8. Sample Size for the Training Set:

The document does not specify the sample size used for the training set. It only describes the "external evaluation" which serves as the validation or test set.

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

Since the training set sample size is not specified, the method for establishing its ground truth is also not explicitly stated. However, given the nature of the device and the validation method, it's highly probable that if a training set was used for algorithm development, its ground truth would also have been established using the CLSI broth microdilution reference method, similar to the test set.

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