(98 days)
chromID™ MRSA agar is a selective and differential chromogenic medium for the qualitative detection of nasal colonization by methicillin-resistant S. aureus (MRSA) to aid in the prevention and control of MRSA infections in healthcare settings. The test is performed on anterior nares swab specimens from patients and healthcare workers to screen for MRSA colonization. chromID™ MRSA agar is not intended to diagnose MRSA infection nor to guide or monitor treatment for infections.
chromID™ MRSA agar is a selective and differential chromogenic medium for the qualitative detection of MRSA from anterior nares swab specimens.
chromID™ MRSA agar consists of a rich nutritive base combining different peptones. It also contains a chromogenic substrate of a-glucosidase and a combination of several antibiotics, which favor the growth of MRSA including hetero-resistant strains. The antibiotics include: cefoxitin (4 mg/l), aztreonam (64 mg/l), and amphotericin B (3 mg/l). The selective mixture of antibiotics inhibits most bacteria not belonging to the genus Staphylococcus, as well as yeasts. The MRSA strains are identified by the presence of green colonies that result from the chromogen incorporated in the medium. The chromogen targets the a-qlucosidase activity of S. aureus. The a-ducosidase produced by S. aureus cleaves the chromogenic substrate, which gives a green color to the S. aureus colonies growing on the medium. This chromogen is identified as "Green a-glucoside" (5-Bromo-4-chloro-3-indoxyl-N-methyl-α-D-glucoside) (patent registered).
- Table of Acceptance Criteria and Reported Device Performance:
| Method Comparison | Acceptance Criteria (Stated) | chromID™ MRSA Reported Performance (95% CI) |
|---|---|---|
| cMRSA | (Not explicitly stated as criteria in this document section, but implied by clinical performance demonstration) | 94.7% (304/321) [91.7 – 96.9%] |
| TSAB | (Not explicitly stated) | 91.6% (294/321) [88.0 – 94.4%] |
| cMRSA vs. Latex Agglutination | (Not explicitly stated) | 96.3% (309/321) [93.6 – 98.1%] |
| cMRSA vs. Cefoxitin Screen | (Not explicitly stated) | 96.3% (309/321) [93.6 – 98.1%] |
| cMRSA vs. mecA PCR | (Not explicitly stated) | 100.0% (321/321) [98.9 – 100%] |
| Non-MRSA (across all methods) | (Not explicitly stated) | Ranging from 97.9% to 100.0% (918/938 to 938/938) |
| Overall Agreement | (Not explicitly stated) | 98.6% (1242/1259) at 24h |
Note: The document states "Clinical studies were performed and demonstrate acceptable performance of chromID™ MRSA," but specific pre-defined acceptance criteria values are not explicitly listed in this excerpt.
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Sample Size Used for the Test Set and Data Provenance:
- Test Set Sample Size:
- MRSA positive samples: 321
- Non-MRSA samples: 938
- Total samples in clinical performance comparison: 1259 (321 + 938)
- Data Provenance: Not explicitly stated in the provided text (e.g., country of origin, retrospective or prospective).
- Test Set Sample Size:
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Number of Experts Used to Establish the Ground Truth for the Test Set and Qualifications of Those Experts:
- The document implies that "conventional methods including the identification and susceptibility testing" and other specific molecular/phenotypic tests (Latex Agglutination, Cefoxitin Screen, mecA PCR) were used to establish ground truth. However, the exact number of experts involved in analyzing these conventional methods or establishing the final ground truth, nor their specific qualifications, are explicitly mentioned.
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Adjudication Method for the Test Set:
- The document does not explicitly describe an adjudication method for conflicting results. The "Performance is based on the number of true positives detected from either medium during the trial (true positives = number of samples positive by TSAB + number of samples that are false negative by TSAB and positive by chromID™ MRSA)" suggests a hierarchical or combined approach to defining true positives, but not a formal expert adjudication process.
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Multi-Reader Multi-Case (MRMC) Comparative Effectiveness Study:
- No, a Multi-Reader Multi-Case (MRMC) comparative effectiveness study focusing on how much human readers improve with AI vs. without AI assistance was not mentioned. This device is a diagnostic culture medium, not an AI-assisted diagnostic tool for human readers.
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Standalone Performance Study:
- Yes, the clinical performance data presented (e.g., "Clinical Performance Compared to Conventional Methods after 24 h Incubation") represents the standalone performance of the chromID™ MRSA agar against established conventional laboratory methods. The device itself (the agar medium) is the 'algorithm' in this context.
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Type of Ground Truth Used:
- The ground truth was established using a combination of "conventional methods including the identification and susceptibility testing" for S. aureus, and specific tests like TSAB (Trypticase Soy Agar with 5% Sheep Blood), Latex Agglutination, Cefoxitin Screen, and mecA PCR. This indicates a laboratory-based, microbiology ground truth (culture, susceptibility testing, molecular diagnostics).
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Sample Size for the Training Set:
- The document does not provide details on a separate "training set" as this is a traditional diagnostic medium, not a machine learning algorithm that typically requires a distinct training phase with labeled data. The clinical performance data appears to be from the validation/test set.
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How the Ground Truth for the Training Set Was Established:
- As no separate training set is explicitly mentioned or relevant for this type of device (a diagnostic culture medium), there is no information on how its ground truth would have been established.
§ 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).