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The cobas vivoDx MRSA test performed on the cobas vivoDx System is an automated qualitative in vitro diagnostic test for the direct detection of live methicillin-resistant Staphylococcus aureus (MRSA) cells in nasal swab samples from patients who are at risk for nasal colonization by MRSA. The test utilizes selective agents and bioparticles (Smarticles technology) to introduce a luciferase gene into targeted bacteria to create an amplified luminescent signal in only viable (live) MRSA cells. The cobas vivoDx MRSA test is intended to aid in the prevention and control of MRSA infections in healthcare settings. It is not intended to diagnose MRSA infections, nor to guide, or monitor treatment. Concomitant cultures are necessary to recover organisms for epidemiological typing or for further susceptibility testing.

The cobas vivoDx MRSA Collection and Transport Kit is used to collect, transport and store human nasal swab specimens for use with the cobas vivoDx MRSA test.

The cobas vivoDx MRSA test, performed on the cobas vivoDx Instrument, is an automated, phenotypic assay for the direct, qualitative detection of MRSA in nasal swab specimens that are collected and transported to the testing laboratory using the cobas vivoDx MRSA Collection and Transport Kit.

Upon receipt in the laboratory, the test operator vortexes the specimen to elute the target organisms (if present) and transfers an aliquot of the transport medium to an MRSA Test Tube containing a dried bead of a selective reagent (cefoxitin) that is solubilized with the sample. The operator then applies a MRSA Reagent Cap to the Test Tube, briefly vortexes the assembled cartridge and loads it onto the cobas vivoDx Instrument for automated processing.

The MRSA Reagent Cap comprises two reagent-filled blisters, one containing Staphylococcus aureus-specific bacteriophage-based Smarticles that encode the enzyme luciferase, and the other, a luminescent substrate. The cobas vivoDx Instrument automatically completes incubation of the cartridge, addition of the Smarticles and substrate to the test sample, as well as measurement and analysis of the luminescent signal. Results are reported as "Positive" (MRSA detected) or "Negative" (no MRSA detected).

Here's a detailed breakdown of the acceptance criteria and the study proving the device meets them, based on the provided text:

Acceptance Criteria and Device Performance for cobas vivoDx MRSA

1. Table of Acceptance Criteria and Reported Device Performance

The document does not explicitly state "acceptance criteria" but rather presents a clinical study evaluating the device's performance against a reference method (culture). The implied acceptance criteria are the target sensitivity and specificity values.

2. Sample Size for the Test Set and Data Provenance

• Test Set Sample Size: 3,963 evaluable subjects (from 4,198 paired specimens enrolled).
• Data Provenance: Prospective Clinical Study conducted at seven geographically diverse locations in the U.S.

3. Number of Experts Used to Establish Ground Truth and Qualifications

The document refers to a "reference culture method" and "direct culture on chromogenic medium" with subsequent confirmation steps for the ground truth. It does not explicitly state the number or qualifications of experts involved in interpreting these culture results. The process for identifying MRSA colonies on chromogenic medium and confirming identity is described, but not in terms of expert involvement.

4. Adjudication Method for the Test Set

The document does not describe an adjudication method involving experts for cases of discordance between the cobas vivoDx MRSA test and the reference culture. It appears that the reference culture method (direct and enriched culture) was considered the definitive ground truth.

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

No, an MRMC comparative effectiveness study involving human readers improving with AI vs. without AI assistance was not explicitly described or presented in this document. The cobas vivoDx MRSA is an automated diagnostic test, and the evaluation focuses on its standalone performance compared to culture, not its impact on human reader performance.

6. Standalone (Algorithm Only) Performance

Yes, a standalone performance study was done. The entire clinical study described in Section L(3)(a) evaluates the performance of the cobas vivoDx MRSA test (an automated system) against culture methods, without human-in-the-loop assistance. The results presented in Table 15 and 16 directly reflect the standalone performance of the device.

7. Type of Ground Truth Used

The primary ground truth used was reference culture method, specifically "direct and enriched culture" for MRSA. The process involved:

• Direct culture on chromogenic medium.
• "Further 28 subjects were positive by (b) (4) (D) (4)" which implies an additional confirmation or enrichment step.
• Identity of suspected colonies of MRSA on (b) (4) was confirmed following (b) (4), suggesting further laboratory testing for definitive identification.

8. Sample Size for the Training Set

The document does not specify the sample size for the training set. It mentions that "The algorithm was developed using data from known MRSA positive and negative analytical and clinical samples," but no numbers are provided for these training data.

9. How the Ground Truth for the Training Set Was Established

The document states, "The result algorithm for the cobas vivoDx MRSA test uses a series of decision trees to evaluate features of the kinetic luminescent curve obtained after addition of substrate to the test sample. The algorithm was developed using data from known MRSA positive and negative analytical and clinical samples..." This implies that the ground truth for the training set was established through known analytical and clinical samples that were already characterized as MRSA positive or negative, likely via culture or other gold standard methods similar to those used for the clinical study ground truth. However, the exact methods for establishing the ground truth for the training set are not detailed.

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