(78 days)
The BD MAX™ StaphSR assay performed on the BD MAX™ System is an automated qualitative in vitro diagnostic test for the direct detection and differentiation of Staphylococcus aureus (SA) and methicillin-resistant Staphylococcus aureus (MRSA) DNA from nasal swabs in patients at risk for nasal colonization. The test utilizes realtime polymerase chain reaction (PCR) for the amplification of MRSA/SA DNA and fluorogenic target-specific hybridization probes for the detection of the amplified DNA. The BD MAX™ StaphSR assay is intended to aid in the prevention and control of MRSA and SA infections in healthcare settings. It is not intended to diagnose MRSA or SA infections nor guide or monitor treatment for MRSA/SA infections. A negative result does not preclude nasal colonization. Concomitant cultures are necessary to recover organisms for epidemiological typing or for further susceptibility testing.
The BD MAX™ System and the BD MAX™ StaphSR assay are comprised of an instrument with associated hardware and accessories, disposable microfluidic cartridges, master mixes, unitized reagent strips, extraction reagents, and sample buffer tubes. The instrument automates sample preparation including target lysis, DNA extraction and concentration, reagent rehydration, and target nucleic acid amplification and detection using real-time PCR. The assay includes a Sample Processing Control (SPC) that is present in the Extraction Tube. The SPC monitors DNA extraction steps, thermal cycling steps, reagent integrity and the presence of inhibitory substances. The BD MAX™ System software automatically interprets test results. A test result may be called as [SA NEG MRSA NEG (negative)], [SA POS, MRSA POS (MRSA positive)], [SA POS, MRSA NEG (SA positive)] or [SA UNR, MRSA UNR (Unresolved)] based on the amplification status of the target and of the Sample Processing Control. IND (Indeterminate) or INC (Incomplete) results are due to BD MAX™ System failure.
The BD MAX™ StaphSR assay is an automated qualitative in vitro diagnostic test for the direct detection and differentiation of Staphylococcus aureus (SA) and methicillin-resistant Staphylococcus aureus (MRSA) DNA from nasal swabs. The performance of the device was evaluated in both analytical and clinical studies.
1. Table of Acceptance Criteria and Reported Device Performance
The acceptance criteria for the BD MAX™ StaphSR assay are primarily based on achieving certain levels of sensitivity and specificity when compared against a reference method (direct culture complemented by enriched culture). The document details the reported performance for MRSA and SA detection.
Acceptance Criteria and Reported Performance for BD MAX™ StaphSR Assay
| Metric | Acceptance Criteria (Implied) | Reported Performance (Overall) - Compared to Reference Method |
|---|---|---|
| MRSA Detection | High sensitivity and specificity | Sensitivity: 93.1% (95% CI: 88.1%, 96.1%) |
| Specificity: 97.5% (95% CI: 96.8%, 98.1%) | ||
| Positive Predictive Value (PPV): 73.2% (95% CI: 67.8%, 78.3%) | ||
| Negative Predictive Value (NPV): 99.5% (95% CI: 99.1%, 99.7%) | ||
| SA Detection | High sensitivity and specificity | Sensitivity: 92.0% (95% CI: 89.7%, 93.9%) |
| Specificity: 93.1% (95% CI: 91.8%, 94.2%) | ||
| Positive Predictive Value (PPV): 83.4% (95% CI: 81.9%, 85.8%) | ||
| Negative Predictive Value (NPV): 96.8% (95% CI: 96.0%, 97.6%) | ||
| Unresolved Rate | Low unresolved rate | Initial Unresolved Rate: 0.6% (15/2399) |
| Unresolved Rate after Repeat: 0.04% (1/2399) | ||
| Inclusivity | Detection of various MRSA and MSSA strains/genotypes at low LoD | Detected 11 MREJ genotypes, 5 SCCmec types, various PFGE types, VRSA, VISA, and 51 MSSA strains (at 2-3 x LoD). |
| Specificity | No cross-reactivity with non-target organisms | No interference from 57 non-staphylococcal species, 45 CoNS/CoPS strains, 50 MSSA strains, and 17 viruses. |
| Interference | No significant interference from common nasal substances | No reportable interference from 29 substances/microorganisms, except for Tobramycin at a high concentration. |
| Carryover/Cross-Contamination | Low risk of carryover/cross-contamination | 3 false positive results (1.5%) out of 203 expected negative samples due to carry-over. |
| Reproducibility | Consistent results across sites and lots | Site-to-Site & Lot-to-Lot agreement: 100% for MP MRSA & TN, 96.7-97.8% for LP MRSA & LP MSSA. |
2. Sample Size Used for the Test Set and Data Provenance
For the clinical performance studies, a total of 2451 specimens were enrolled. After excluding non-compliant specimens, 2354 specimen results were used to determine the clinical performance against the Reference Method, and 2393 specimen results were used for comparison against Direct Culture.
The data provenance for the clinical study is prospective, collected from three geographically diverse investigational centers. The specific countries of origin for these centers are not explicitly stated.
3. Number of Experts Used to Establish the Ground Truth for the Test Set and Qualifications of Those Experts
The document does not explicitly state the number of experts used to establish the ground truth or their specific qualifications (e.g., radiologist with X years of experience). However, the ground truth was established using laboratory methods rather than expert interpretation of images or clinical assessments.
4. Adjudication Method for the Test Set
The adjudication method for the clinical test set involved a Comparative Reference Method consisting of direct culture complemented by enriched culture.
- For specimens negative for MRSA or SA by direct culture, enriched culture analysis was performed.
- Presumptive S. aureus colonies on chromogenic medium were subcultured onto Blood Agar (BA) for identification confirmation with an agglutination test.
- Methicillin resistance was confirmed by Cefoxitin disk (30 µg) diffusion susceptibility testing.
- Enrichment in Trypticase Soy Broth with 6.5% NaCl was carried out if MRSA or SA was not confirmed by initial direct culture.
- Turbid TSB 6.5% NaCl broth was used to inoculate additional chromogenic medium and BA plates, and MRSA confirmation followed the same procedure.
- Further investigation was performed on specimens with discordant results between the Reference Method and the BD MAX™ StaphSR assay. For MRSA, 12 of 54 false positive and 5 of 11 false negative BD MAX™ StaphSR specimens were re-evaluated by the Reference Method. For SA, 28 of 118 false positive and 23 of 52 false negative BD MAX™ StaphSR specimens were re-evaluated by the Reference Method.
5. If a Multi Reader Multi Case (MRMC) Comparative Effectiveness Study Was Done, What was the Effect Size of How Much Human Readers Improve with AI vs Without AI Assistance
This information is not applicable as the BD MAX™ StaphSR assay is an automated in vitro diagnostic test (molecular assay) for direct detection of DNA. It does not involve "human readers" or AI assistance in the interpretation of results in the context of an MRMC study. The device provides an automated interpretation of results.
6. If a Standalone (i.e., algorithm only without human-in-the-loop performance) Was Done
Yes, a standalone performance study was done. The BD MAX™ StaphSR assay is an automated instrument-based test that directly provides a qualitative result ([SA NEG MRSA NEG], [SA POS, MRSA POS], [SA POS, MRSA NEG], or [SA UNR, MRSA UNR]). The clinical performance data presented in Tables 10-17 directly reflect the standalone performance of the assay compared to the reference microbiological methods.
7. The Type of Ground Truth Used
The ground truth used for both the analytical and clinical studies was based on microbiological culture methods:
- Direct culture complemented by enriched culture for clinical performance evaluation.
- Cultured bacterial suspensions and well-characterized clinical isolates for analytical studies (e.g., LoD, inclusivity, specificity, competitive inhibitory effect).
8. The Sample Size for the Training Set
The document describes premarket studies for a diagnostic device. For such devices, there isn't typically a "training set" in the machine learning sense. Instead, development and optimization are performed using various analytical samples and potentially some initial clinical samples, followed by a robust validation (clinical performance) on an independent set. The details of any specific samples used for internal development or optimization (analogous to a training set) are not provided in this 510(k) summary. The provided sample sizes relate to the analytical validation and the final clinical validation dataset.
9. How the Ground Truth for the Training Set Was Established
Given that this is a molecular diagnostic assay and not an AI/ML-based image interpretation product, the concept of a "training set" with ground truth established in that context is not directly applicable. If one were to consider the samples used for assay development and optimization as a "training set," their ground truth would have been established through known bacterial cultures (characterized strains, quantified suspensions) and potentially well-characterized clinical isolates with confirmed microbiological status (e.g., through traditional culture, biochemical tests, and susceptibility testing). However, specific details of such "pre-validation" ground truth establishment are not provided in this regulatory summary.
§ 866.1640 Antimicrobial susceptibility test powder.
(a)
Identification. An antimicrobial susceptibility test powder is a device that consists of an antimicrobial drug powder packaged in vials in specified amounts and intended for use in clinical laboratories for determining in vitro susceptibility of bacterial pathogens to these therapeutic agents. Test results are used to determine the antimicrobial agent of choice in the treatment of bacterial diseases.(b)
Classification. Class II (performance standards).