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The NucliSENS EasyQ® MRSA assay is a qualitative in vitro diagnostic test for the direct detection of methicillin-resistant Staphylococcus aureus (MRSA) from nasal swabs in patients at risk for nasal colonization. The NucliSENS EasyQ® MRSA assay is performed on the NucliSENS EasyQ® platform.

The test utilizes NASBA™ (nucleic acid sequence-based amplification) coupled with molecular beacons (sequence-specific fluorescent probes) to detect the presence of MRSA DNA.

The NucliSENS EasyQ® MRSA assay is used as a screening tool to aid in the prevention and control of MRSA infections in health care institutions.

NucliSENS EasyQ® MRSA is not intended to diagnose, quide or monitor treatment for MRSA infections, or provide results of susceptibility to methicillin. A negative result does not preclude MRSA nasal colonization. Concomitant cultures are necessary to recover organisms for epidemiological typing or for further susceptibility testing.

The NucliSENS EasyQ® MRSA assay is a qualitative in vitro diagnostic test for the direct detection of methicillin-resistant Staphylococcus aureus (MRSA) from nasal swabs. The test utilizes NASBA™ (nucleic acid sequence-based amplification) coupled with molecular beacons (sequence-specific fluorescent probes) to detect the presence of MRSA DNA. The assay is performed on the NucliSENS EasyQ® platform, which includes the NucliSENS EasyQ® Analyzer, NucliSENS EasyQ® Incubator II, NucliSENS EasyQ® Computer, Monitor, Printer, and NucliSENS EasyQ® Director Software 2.6. The assay involves manual specimen processing from a dry flocked nasal swab, followed by automated amplification and detection in a closed tube format. Result calculation is performed automatically via dedicated operator software based on the analysis of fluorescence signal curves. Qualitative output (MRSA positive, MRSA negative or invalid) is reported to users. The assay includes an inhibition control and run controls (blank and positive control). Specimen preparation controls are recommended but not provided in the kit.

Acceptance Criteria and Device Performance for NucliSENS EasyQ® MRSA Assay

1. Table of Acceptance Criteria and Reported Device Performance

The submission document primarily reports the performance metrics rather than explicitly stating pre-defined acceptance criteria with specific threshold values for each. However, based on the statistical results and the general context of medical device submissions, we can infer the implied acceptance criteria.

2. Sample Size Used for the Test Set and Data Provenance

• Clinical Study Test Set:

  • Total specimens collected: 1355 nasal specimens.
  • Final evaluable specimens for analysis: 1238 specimens (117 excluded due to non-compliance with clinical protocol).
  • Data Provenance:
    • Country of Origin: US (7 geographically diverse institutions in the US).
    • Retrospective or Prospective: Prospective investigational study.

• Analytical Test Sets:

  • Analytical Sensitivity (LOD): 24 replicates for each bacterial input for each of the seven MREJ types.
  • Analytical Specificity: Fresh cultures from 100 phylogenetically related S. aureus and members of the nasal commensal flora (26 MRCoNS, 29 MSSCoNS, 25 MSSA, 20 other non-staphylococci).
  • Analytical Reactivity: Fresh cultures from 193 MRSA strains.
  • Precision (Within-laboratory): 3 replicates per run for three different bacterial inputs (High Negative, Low Positive, Moderate Positive) over 12 days.
  • Precision (Between-laboratory): 3 replicates per run for four different bacterial inputs (High Negative, Low Positive, Low Positive 2, Moderate Positive) at 3 sites over 6 days.
  • Carry-Over Contamination: 105 high MRSA positive and 105 MRSA negative samples (divided over 5 EasyQ runs).

3. Number of Experts Used to Establish the Ground Truth for the Test Set and Qualifications

The ground truth for the clinical test set was established by a reference enriched culture method. The document does not specify the number or qualifications of experts involved in performing or interpreting these reference culture results. It only states that "suspect S. aureus colonies were confirmed with a Gram stain and latex agglutination test" and "Confirmed S. aureus colonies were tested for methicillin resistance using the cefoxitin disk test as described in CLSI M2A9 and CLSI M100 S17." This implies standard microbiological laboratory practices, but not explicitly "experts" in the sense of physicians or highly experienced scientists directly establishing ground truth beyond the protocol.

4. Adjudication Method for the Test Set

There is no mention of an adjudication method for the clinical test set. The comparison is directly between the NucliSENS EasyQ® MRSA assay results and the reference enriched culture method. Discrepancies are not stated to have undergone expert review or further adjudication.

5. If a Multi-Reader Multi-Case (MRMC) Comparative Effectiveness Study was done

No, an MRMC comparative effectiveness study was not done. This device is an automated in vitro diagnostic test that provides a qualitative output (MRSA positive, MRSA negative, or invalid). Its performance is directly compared to a reference culture method, not to human readers' performance, either with or without AI assistance. Therefore, there is no effect size reported for human readers improving with AI vs. without AI assistance.

6. If a Standalone (i.e., algorithm only without human-in-the-loop performance) was done

Yes, a standalone (algorithm only) performance study was done. The NucliSENS EasyQ® MRSA assay operates as an automated system, comprising reagents, instrumentation (EasyQ® Analyzer, Incubator), and dedicated software for result calculation. The "Performance Characteristics" section, including clinical performance, analytical sensitivity, specificity, reactivity, and precision, describes the performance of the device algorithm and system in isolation, without human interpretation or intervention in the final result determination from the EasyQ system beyond initial sample preparation.

7. The Type of Ground Truth Used

• Clinical Study Ground Truth: Reference enriched culture method. This method involved:
  • Direct inoculation of a nasal swab into Trypticase Soy Broth (TSB) with 6.5% NaCl, incubated for 18-24 hours.
  • Streaking the enrichment broth onto a Blood Agar Plate (BAP) and incubating for 24-48 hours.
  • Confirming suspect S. aureus colonies with Gram stain and latex agglutination test.
  • Testing confirmed S. aureus for methicillin resistance using the cefoxitin disk test (CLSI M2A9 and CLSI M100 S17).
  • This is a labor-intensive, gold-standard microbiological method for MRSA detection.

8. The Sample Size for the Training Set

The document does not explicitly specify a sample size for a "training set" for the algorithm. This is common for older diagnostic devices, particularly PCR/NASBA-based assays, where the algorithm for calling positive/negative is typically rule-based on fluorescence curves and thresholding, rather than a machine learning model developed with a distinct training set. The "software design documentation" for the MRSA assay protocol is mentioned, indicating the development of the algorithm based on established principles rather than data-driven machine learning training.

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

As there is no explicit mention of a training set or a machine learning algorithm that required one, the concept of establishing ground truth for a training set is not directly applicable in the terms usually associated with modern AI/ML device submissions. The assay relies on the well-understood biochemical principles of NASBA™ amplification and molecular beacon detection for targets (SCCmec cassette junction and mecA gene) that define MRSA. The "ground truth" for the development of the primers and probes would have been established through extensive genomic sequencing data ("Sequence alignments" section mentions 319 MRSA strains from public databases) and experimental validation in the laboratory to ensure accurate detection of target sequences.

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