(262 days)
MRSASelect™II is a selective and differential chromogenic medium for:
A) The qualitative detection of nasal colonization of methicillin-resistant Staphylococcus aureus (MRSA) to aid in the prevention and control of MRSA infections in healthcare settings. The test can be performed on anterior nares specimens from patients to screen for MRSA colonization. MRSASelect™II is not intended to diagnose MRSA infection nor to guide or monitor treatment of infection. A negative result does not preclude MRSA nasal colonization. Concomitant cultures are necessary to recover organisms for identification, antimicrobial susceptibility testing, or epidemiological typing. Results can be interpreted after 18 to 28 hours incubation.
B) The qualitative detection of methicillin-resistant Staphylococcus aureus (MRSA) from skin and soft tissue wound specimens. The MRSASelect™II is indicated for use in conjunction with other laboratory tests and clinical data available to aid in the identification and diagnosis of MRSA from patients with skin and soft-tissue infections. Concomitant cultures and antimicrobial susceptibility testing are necessary for all skin and soft-tissue wound specimens. MRSASelect™I is not intended to guide, or monitor treatment for MRSA infection, or provide results of susceptibility to methicillin. Results can be interpreted after 18 to 28 hours incubation.
MRSASelect™I is a selective medium for the detection and direct identification of MRSA. The selectivity of this medium is based on the presence of an antibiotic/antifungal mixture and an optimized salt concentration that inhibits the growth of yeasts and the majority of Gram negative and Gram positive bacteria, with the exception of methicillin-resistant staphylococci. Identification is based on the cleavage of a chromogenic substrate by a specific enzymatic activity of Staphylococcus aureus, leading to a strong pink coloration of the Staphylococcus aureus colonies. Plates may be read within 18-28 hours incubation:
- Methicillin-resistant Staphylococcus aureus produces pink colonies on MRSASelect™II;
- . Coagulase negative methicillin-resistant staphylococci may not grow or may grow as colorless or white colonies;
- Methicillin-susceptible staphylococci (MSS) are inhibited.
Here's an analysis of the provided text, focusing on the acceptance criteria and the study proving the device meets them, presented in the requested format.
This document describes the premarket notification (510(k)) for the MRSASelect™II device, a culture medium for detecting methicillin-resistant Staphylococcus aureus (MRSA). The information provided is for a diagnostic device (culture medium) and not an AI device. Therefore, some of the requested categories (e.g., number of experts for ground truth, MRMC study, training set information) are not directly applicable or are not detailed in the same way they would be for an AI/ML medical device submission. However, an effort will be made to extract comparable information where possible.
Acceptance Criteria and Reported Device Performance
The acceptance criteria for a diagnostic culture medium are typically established as performance targets for sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) against a reference method. These are not explicitly stated as "acceptance criteria" with numerical thresholds to be met, but the clinical performance data provided demonstrates the device's accuracy.
Table 1: Acceptance Criteria (Implied Performance Targets) and Reported Device Performance
| Performance Metric | Implied Acceptance Criteria (Typical for such devices) | Reported Device Performance (Wound Samples - Table 3) | Reported Device Performance (Anterior Nares Samples - Table 4) |
|---|---|---|---|
| Sensitivity | High (e.g., >90%) | 96.7% (95% C.I.: 96.0%-97.5%) | 91.0% (95% C.I.: 86.8%-93.9%) |
| Specificity | High (e.g., >90%) | 95.4% (95% C.I.: 94.5%-96.2%) | 98.3% (95% C.I.: 97.6%-98.8%) |
| Positive Predictive Value (PPV) | High | 82.1% (95% C.I.: 80.5%-83.7%) | 86.2% (95% C.I.: 81.6%-89.9%) |
| Negative Predictive Value (NPV) | High | 99.2% (95% C.I.: 98.9%-99.6%) | 98.9% (95% C.I.: 98.4%-99.3%) |
Note on "Acceptance Criteria": For traditional in vitro diagnostic devices like culture media, the "acceptance criteria" are typically defined internally by the manufacturer during product development and validation, often based on predicate device performance or clinical utility. The FDA then evaluates whether the provided performance data supports the claim of substantial equivalence. The tables above reflect the achieved performance which the FDA deemed acceptable for substantial equivalence.
Study Details
Given that this is a 510(k) for a culture medium (not an AI device), some of the requested information directly pertaining to AI/ML device studies will not be present in the document.
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Sample size used for the test set and the data provenance:
- Total Clinical Samples: 3,252 prospective valid wound and anterior nares specimens.
- Wound Samples (Test Set): 842 specimens.
- Anterior Nares Samples (Test Set): 2,410 specimens.
- Data Provenance:
- Country of Origin: United States.
- Retrospective or Prospective: Prospective. Specimens were collected from 2013 to 2016.
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Number of experts used to establish the ground truth for the test set and the qualifications of those experts:
- This information is not directly stated in the document as it would be for an AI imaging study involving human readers. For diagnostic culture media, ground truth is established by specific, well-defined laboratory reference methods. The document describes a multi-step microbiological process for establishing ground truth, involving culture enrichment, subculturing, Gram stain, agglutination tests, tube coagulase, and for MRSA confirmation PBP2a testing and mecA-mediated oxacillin resistance testing. The execution of these laboratory methods implies the involvement of qualified laboratory personnel (e.g., clinical microbiologists, medical technologists), but specific numbers or qualifications are not specified in the document in the format relevant to expert readers of AI output.
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Adjudication method (e.g., 2+1, 3+1, none) for the test set:
- Not applicable in the context of human reader adjudication for an AI device. For discordant results between the device and the reference method, "Discordant analysis" was performed (e.g., for wound samples, PBP2a test was used; for anterior nares, specific non-S. aureus and MSSA determinations were made). This is a laboratory-based adjudication of the samples themselves, not an adjudication of human interpretations.
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If a multi-reader, multi-case (MRMC) comparative effectiveness study was done:
- No. An MRMC study is relevant for comparing human reader performance with and without an AI device. This submission is for a culture medium, not an AI device.
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If a standalone (i.e., algorithm only without human-in-the-loop performance) was done:
- Yes, effectively. The performance of the MRSASelect™II device itself, without human interpretation beyond reading the chromogenic results, was assessed against the established reference methods. This "standalone" performance is what the sensitivity, specificity, PPV, and NPV data represent.
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The type of ground truth used (expert consensus, pathology, outcomes data, etc.):
- Laboratory Reference Method / Microbiological Culture Confirmation: The ground truth was established by using standard microbiological culture enrichment broth methods (Tryptic Soy Broth with 6.5% NaCl) followed by definitive identification tests for Staphylococcus aureus (Gram stain, slide agglutination, tube coagulase) and confirmation of methicillin resistance (PBP2a testing for anterior nares; mecA-mediated oxacillin resistance testing using cefoxitin disk for wound samples, with PBP2a for discordant wound samples). This is a gold standard for bacterial identification and resistance.
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The sample size for the training set:
- This document describes a clinical performance study (test set) for device validation, not an AI/ML model. Therefore, there's no explicitly defined "training set" in the context of machine learning. The device design and refinement would have been based on internal R&D, potentially involving earlier, smaller studies or characterization data, but these are not disclosed as a "training set" in this document.
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How the ground truth for the training set was established:
- Not applicable as there is no specific "training set" described for an AI/ML model. The design and analytical validation of the culture medium (e.g., Analytical Sensitivity (Inclusivity) testing with 54 characterized MRSA strains, Analytical Specificity (Cross Reactivity) with 109 strains, Precision/Reproducibility using ATCC® strains) demonstrate how the device's fundamental properties were confirmed against known bacterial strains/isolates, which serve as an equivalent to a "ground truth" for analytical performance.
§ 866.1700 Culture medium for antimicrobial susceptibility tests.
(a)
Identification. A culture medium for antimicrobial susceptibility tests is a device intended for medical purposes that consists of any medium capable of supporting the growth of many of the bacterial pathogens that are subject to antimicrobial susceptibility tests. The medium should be free of components known to be antagonistic to the common agents for which susceptibility tests are performed in the treatment of disease.(b)
Classification. Class II (performance standards).