(71 days)
The Cepheid Xpert® Flu Assay, performed on the GeneXpert® Instrument Systems, is an automated, multiplex real-time RT-PCR assay intended for the in vitro qualitative detection and differentiation of influenza A, influenza B and 2009 H1N1 influenza viral RNA. The Xpert Flu Assay uses nasal aspirates/washes and nasopharyngeal swab specimens collected from patients with signs and symptoms of respiratory infection in conjunction with clinical and epidemiological risk factors. The Xpert Flu Assay is intended as an aid in the diagnosis of influenza.
Negative results do not preclude influenza virus infection and should not be used as the sole basis for treatment or other patient management decisions.
Performance characteristics for influenza A were established during the 2009-2010 influenza season when 2009 H1N1 influenza was the predominant influenza A virus in circulation. Performance characteristics for influenza A were confirmed when influenza A/H3 and influenza A/2009 H1N1 were the predominant influenza A viruses in circulation (2009-2010, 2010-2011 and 2011-2012). When other influenza A viruses are emerging, performance characteristics may vary.
If infection with a novel influenza A virus is suspected based on current clinical and epidemiological screening criteria recommended by public health authorities, specimens should be collected with appropriate infection control precautions for novel virulent influenza viruses and sent to state or local health department for testing. Viral culture should not be attempted in these cases unless a BSL 3+ facility is available to receive and culture specimens.
The Xpert Flu Assay is a rapid, automated in vitro diagnostic test for qualitative detection and differentiation of influenza A, influenza B and influenza A, subtype 2009 H1N1. The assay is performed on the Cepheid GeneXpert Instrument Systems. The GeneXpert Instrument Systems automate and integrate sample purification, nucleic acid amplification, and detection of the target sequence in simple or complex samples using real-time PCR and RT-PCR assays. The systems require the use of single-use disposable cartridges that hold the PCR reagents and host the PCR process. Because the cartridges are self-contained and specimens never come into contact with working parts of the instrument modules, cross-contamination between samples is minimized.
The Xpert Flu Assay includes reagents for the detection and differentiation of influenza A, influenza B and influenza A, subtype 2009 H1N1 directly from nasal aspirates/washes (NA/W) and nasopharyngeal (NP) swab specimens from patients suspected of having influenza. A Sample Processing Control (SPC) and a Probe Check Control (PCC) are also included. The SPC is present to control for adequate processing of the target viruses and to monitor the presence of inhibitors in the PCR reaction. The Probe Check Control (PCC) verifies reagent rehydration, PCR tube filling in the cartridge, probe integrity and dye stability.
The liquid specimen (NA/W) or swab specimen (NP) is collected according to the institution's standard procedures and placed into Universal Transport Medium (3mL UTM tubes). Following a brief mixing by inverting the UTM tube five times, the eluted material and one single-use reagent (Reagent 1), that is provided with the assay, are transferred to different, uniquely-labeled chambers of the disposable fluidic cartridge (the Xpert Flu cartridge). The user initiates a test from the system user interface and places the cartridge into the GeneXpert instrument platform, which performs hands-off realtime, multiplex polymerase chain reaction (PCR) for detection of DNA. In this platform, additional sample preparation, amplification, and real-time detection are all fullyautomated and completely integrated.
The single-use, multi-chambered fluidic cartridges are designed to complete sample preparation and real-time PCR for detection and differentiation of influenza A. influenza B and influenza A, subtype 2009 H1N1 in 75 minutes. The GeneXpert Instrument Systems, which consist of the GeneXpert Dx System, the GeneXpert Infinity-48 System, and the GeneXpert Infinity-80 System, have 1 to 80 randomly accessible modules that are each capable of performing separate sample preparation and real-time PCR tests. Each module contains a syringe drive for dispensing fluids (i.e., the syringe drive activates the plunger that works in concert with the rotary valve in the cartridge to move fluids between chambers), an ultrasonic horn for lysing cells or spores, and a proprietary I-CORE® thermocycler for performing real-time PCR and detection.
The Cepheid Xpert® Flu Assay, a molecular diagnostic device, was evaluated through analytical and clinical performance studies to demonstrate its substantial equivalence to a previously cleared predicate device (K120911).
1. Acceptance Criteria and Reported Device Performance
The acceptance criteria for the Xpert Flu Assay, as demonstrated by its performance against a predicate device, are based on positive and negative agreement rates for the detection of influenza A, influenza A subtype 2009 H1N1, and influenza B in different specimen types (Nasal Aspirates/Washes and Nasopharyngeal Swabs). While explicit numerical acceptance criteria are not presented as thresholds, the observed performance values for the modified Xpert Flu Assay are provided as evidence of its substantial equivalence.
Table of Acceptance Criteria and Reported Device Performance:
| Specimen Type | Target | Positive Agreement % (95% CI) | Negative Agreement % (95% CI) |
|---|---|---|---|
| NA/W | Influenza A | 100 (97.5-100) | 98.1 (94.5-99.6) |
| NA/W | Influenza A subtype 2009 H1N1 | 97.1 (89.8-99.6) | 99.6 (97.6-100) |
| NA/W | Influenza B | 100 (84.6-100) | 99.6 (98.0-100) |
| NP Swab | Influenza A | 100 (97.8-100) | 95.2 (91.1-97.8) |
| NP Swab | Influenza A subtype 2009 H1N1 | 98.5 (92.1-100) | 99.6 (98.1-100) |
| NP Swab | Influenza B | 100 (87.2-100) | 99.1 (97.3-99.8) |
The study demonstrates that the modified Xpert Flu Assay exhibits very high positive and negative agreement rates when compared to the predicate Xpert Flu Assay across all targets and specimen types.
2. Sample Size Used for the Test Set and Data Provenance
The clinical performance study used a total of 302 Nasal Aspirate/Wash (NA/W) specimens and 352 Nasopharyngeal (NP) swab specimens for the test set.
The data provenance for these specimens is described as:
- Retrospective/Prospective: The specimens included a mix of "frozen leftover, prospectively collected, unlinked prospectively collected archived and/or pre-selected banked" specimens.
- Country of Origin: Not explicitly stated, but assumed to be from locations where standard clinical influenza testing is conducted, given the context of US FDA submission.
Additionally, ten contrived specimens (5 NP swab and 5 NA/W) were prepared and tested separately. These were not included in the primary dataset analysis of agreement rates.
3. Number of Experts Used to Establish Ground Truth for the Test Set and Qualifications
Not applicable. This is a molecular diagnostic device comparing its performance to a predicate molecular diagnostic device. The ground truth for the clinical performance study was established by the predicate device's results, with sequencing used for discrepant results. No human expert interpretation of images or clinical findings for ground truth establishment is mentioned.
4. Adjudication Method for the Test Set
The adjudication method specifically mentioned for the clinical performance study was sequencing for all discrepant specimens. This means if the modified Xpert Flu Assay result differed from the predicate Xpert Flu Assay result, a third, independent method (sequencing) was used to determine the true positive/negative status for those particular samples.
5. Multi-Reader Multi-Case (MRMC) Comparative Effectiveness Study
No, a Multi-Reader Multi-Case (MRMC) comparative effectiveness study was not done. This device is an automated, standalone diagnostic assay, not an AI-assisted human reading system. Therefore, the concept of human readers improving with AI vs. without AI assistance is not applicable.
6. Standalone Performance Study
Yes, a standalone performance study was done. The entire evaluation of the "modified Xpert Flu Assay" against the "current Xpert Flu Assay" (the predicate device) represents its standalone performance. The device provides a qualitative detection and differentiation of influenza A, B, and 2009 H1N1 viral RNA directly from patient specimens without human interpretation of the assay's primary output beyond reading the automated result.
7. Type of Ground Truth Used
For the clinical performance study, the primary ground truth was implicitly the results from the predicate Xpert Flu Assay. For any discrepancies between the modified device and the predicate, sequencing was used as the confirmatory ground truth.
For the analytical studies (Analytical Reactivity and Limit of Detection), the ground truth for positive results was known viral strains at defined concentrations (TCID50/mL or pg/µL). For Analytical Specificity, the ground truth was known non-target viral, bacterial, and yeast strains.
8. Sample Size for the Training Set
Not applicable. This is a molecular diagnostic test. The concept of a "training set" is typically associated with machine learning or AI models. For this type of device, performance is established through analytical validation (known concentrations of specific strains) and clinical validation (comparison to a predicate or established reference method in patient samples). There is no mention of a machine learning component requiring a distinct training set.
9. How the Ground Truth for the Training Set Was Established
Not applicable, as there was no explicit training set for a machine learning model. For the analytical and clinical studies, ground truth was established as described in section 7.
§ 866.3980 Respiratory viral panel multiplex nucleic acid assay.
(a)
Identification. A respiratory viral panel multiplex nucleic acid assay is a qualitative in vitro diagnostic device intended to simultaneously detect and identify multiple viral nucleic acids extracted from human respiratory specimens or viral culture. The detection and identification of a specific viral nucleic acid from individuals exhibiting signs and symptoms of respiratory infection aids in the diagnosis of respiratory viral infection when used in conjunction with other clinical and laboratory findings. The device is intended for detection and identification of a combination of the following viruses:(1) Influenza A and Influenza B;
(2) Influenza A subtype H1 and Influenza A subtype H3;
(3) Respiratory Syncytial Virus subtype A and Respiratory Syncytial Virus subtype B;
(4) Parainfluenza 1, Parainfluenza 2, and Parainfluenza 3 virus;
(5) Human Metapneumovirus;
(6) Rhinovirus; and
(7) Adenovirus.
(b)
Classification. Class II (special controls). The special controls are:(1) FDA's guidance document entitled “Class II Special Controls Guidance Document: Respiratory Viral Panel Multiplex Nucleic Acid Assay;”
(2) For a device that detects and identifies Human Metapneumovirus, FDA's guidance document entitled “Class II Special Controls Guidance Document: Testing for Human Metapneumovirus (hMPV) Using Nucleic Acid Assays;” and
(3) For a device that detects and differentiates Influenza A subtype H1 and subtype H3, FDA's guidance document entitled “Class II Special Controls Guidance Document: Testing for Detection and Differentiation of Influenza A Virus Subtypes Using Multiplex Nucleic Acid Assays.” See § 866.1(e) for the availability of these guidance documents.