(218 days)
MRSASelect is a selective and differential chromogenic medium for 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 and healthcare workers to screen for MRSA colonization. MRSASelect is not intended to diagnose MRSA infection nor to guide or monitor treatment of infection.
The Bio-Rad MRSASelect is a selective and differential chromogenic culture medium for the qualitative detection of MRSA from anterior nares specimens. The selectivity of this medium is based on the presence of an antibiotic/antifungal mixture and an optimized salt concentration and that inhibits the growth of yeast 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.
Here's an analysis of the Bio-Rad MRSASelect Culture Media device, based on the provided 510(k) submission information:
1. Table of Acceptance Criteria and Reported Device Performance
The submission does not explicitly state pre-defined acceptance criteria for the performance metrics (sensitivity, specificity, PPV, NPV). However, the device performance is compared against two different "ground truth" methods: Routine Culture and CHROMagar. We can infer that the reported performance metrics were deemed acceptable by the FDA for substantial equivalence.
| Metric | Acceptance Criteria (Inferred) | Reported Performance (vs. Routine Culture) | Reported Performance (vs. CHROMagar) |
|---|---|---|---|
| Sensitivity | Not explicitly stated | 96% | 94% |
| Specificity | Not explicitly stated | 98% | 99% |
| PPV (Positive Predictive Value) | Not explicitly stated | 87% | 92% |
| NPV (Negative Predictive Value) | Not explicitly stated | 99% | 99% |
| Agreement | Not explicitly stated | 98% (agreement to routine culture) | 99% (agreement to CHROMagar) |
2. Sample Size Used for the Test Set and Data Provenance
- Sample Size: A total of 3013 anterior nares samples were evaluated.
- Data Provenance:
- Country of Origin: Not explicitly stated, but the study was conducted at "three geographically diverse hospitals." This suggests the data is likely from the country where these hospitals are located, which could be France (where Bio-Rad is headquartered) or potentially the US given the submission to the FDA.
- Retrospective or Prospective: Prospective. The study mentions "fresh surveillance specimens of the anterior nares samples," indicating real-time collection for the study.
3. Number of Experts Used to Establish the Ground Truth for the Test Set and Qualifications of Those Experts
The submission does not specify the number of experts or their qualifications involved in establishing the ground truth. It refers to "Routine Culture which was defined as isolation on Staphylococci on Trypticase Soy Agar with 5% blood, with identification confirmed by Coagulase and Oxacillin susceptibility." While these are standard laboratory procedures, the expertise for their interpretation is implied to be within usual clinical laboratory practice, but no specific expert qualifications are provided.
4. Adjudication Method for the Test Set
The submission does not describe an adjudication method for the test set. The results are presented as direct comparisons between the MRSASelect medium and the reference methods (Routine Culture and CHROMagar). This typically implies a direct comparison of results without a separate ad-hoc adjudication process for discordant results, though standard lab protocols for resolving discrepancies or verifying results would be assumed.
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
This document describes a diagnostic culture medium, not an AI-powered device. Therefore, a Multi-Reader Multi-Case (MRMC) comparative effectiveness study focusing on human reader improvement with/without AI assistance is not applicable and was not performed.
6. If a Standalone (i.e., algorithm only without human-in-the-loop performance) Was Done
Again, this is a culture medium, not an algorithm. The "standalone" performance described here is the performance of the culture medium itself, interpreted by laboratory personnel, in detecting MRSA. There is no AI algorithm involved.
7. The Type of Ground Truth Used
Two types of ground truth were used:
- Routine Culture: Defined as "isolation on Staphylococci on Trypticase Soy Agar with 5% blood, with identification confirmed by Coagulase and Oxacillin susceptibility." This is a gold standard for bacterial identification and susceptibility testing in microbiology.
- BD BBL™ CHROMagar™ MRSA: This is a predicate device, which itself functions as a selective and differential chromogenic medium for MRSA detection. While a predicate, it is used here as a comparative reference, implying its results are also considered a reliable truth for comparison.
8. The Sample Size for the Training Set
The submission does not explicitly mention a "training set" as this is a traditional diagnostic assay (culture medium) and not a machine learning model. Therefore, the concept of a separate training set for algorithm development is not applicable here. The entire 3013 samples represent the validation/test set for the device's performance.
9. How the Ground Truth for the Training Set Was Established
As no training set (in the machine learning sense) was used, this question is not applicable. The existing knowledge and established methods of microbiology (e.g., specific enzyme activities, antibiotic resistance, chromogenic reactions) form the basis for how the culture medium is designed to detect MRSA.
§ 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).