(53 days)
The Cepheid Xpert® Flu Assay 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. 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 enidemiological 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 Cepheid Xpert® Flu Assay is a rapid, automated in vitro diagnostic test for qualitative detection and differentiation of influenza B, and influenza A, subtype 2009 H1N1 from nasal aspirates/washes (NA/W) and nasopharyngeal (NP) swab specimens from patients with signs and symptoms of respiratory infection. The assay is performed on the Cepheid GeneXpert Instrument Systems, which consist of the GeneXpert Dx System and the GeneXpert Infinity-48 System. The Device is being modified with this 510(k), to add the GeneXpert Infinity-80 System as an additional instrument system for use with the Xpert Flu Assay.
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 rRT-PCR assays. The GeneXpert Instrument System family comprises a GeneXpert (GX) instrument, GX-I, GX-IV, GX-XVI; a GeneXpert XVI, available with 4, 8, 12 or 16 modules, a GeneXpert Infinity-48 available with 16, 24, 32 or 48 modules, or a GeneXpert Infinity-80 available with 16, 24, 32, 40, 48, 56, 64, 72, or 80 modules. The instrument systems also contain a computer, and preloaded software for running tests and viewing the results. The GeneXpert Infinity Systems contain robotic features for cartridge handling. Each module contains a syringe drive for dispensing fluids, an ultrasonic horn for lysing cells or spores, a valve drive for sample movement, and I-CORE® thermocycler for performing real-time PCR and detection.
All systems require the use of the assay-specific single-use disposable cartridges that hold the PCR reagents and host the PCR process. The patented single-use cartridges contain: (1) eleven chambers for holding sample, reagents, or other materials, (2) a valve body composed of a plunger and syringe barrel, (3) a rotary valve system for controlling the movement of fluids between chambers, (4) an area for capturing, concentrating, washing, and lysing cells, (5) dry real-time PCR reagents, (6) an integrated PCR reaction tube that can be automatically filled by the instrument, and (7) liquid reagents. To eliminate testto-test contamination, all fluids including amplicons, are contained within the disposable cartridge. The instrument never comes into contact with any fluids within the cartridge. Each disposable cartridge is intended to test one sample. Cartridges are not re-usable.
A sample processing control (SPC) and a system control (Probe Check Control) are controls utilized by the GeneXpert Instrument System platform. The SPC is pre-loaded into the GeneXpert cartridge provided with the assay. The SPC is an encapsidated RNA made up of recombinant fragments developed so that there is no homology to the influenza genome. The SPC is present to control for adequate processing of the target viruses and to monitor the presence of inhibitors in the PCR reaction to reduce the possibility of false negative results. The SPC also ensures the PCR reaction conditions (temperature and time) are appropriate for the amplification reaction and that the PCR reagents are functional. The Probe Check Control verifies reagent rehydration, PCR tube filling in the cartridge, probe integrity and dye stability.
Commercially-available external controls may also be run in accordance with local, state, and federal accrediting organizations, as applicable.
The Xpert Flu Assay includes reagents for the simultaneous detection and differentiation of the target viruses. The primers and probes in the Xpert Flu Assay detect the presence of nucleic acid sequences for influenza A (Flu A), influenza B (Flu B) and influenza A sub-type 2009 H1N1 (2009 H1N1) directly from nasal aspirates/washes (NA/W) and nasopharyngeal (NP) swab specimens collected from patients suspected of having influenza. The specimens are collected in Universal Transport Medium (UTM) and transported to the GeneXpert area.
The specimen is prepared according to package insert instructions and transferred to the sample chamber (large opening) of the Xpert Flu Assay Cartridge. Reagent 1 (Binding Reagent) is dispensed into the chamber with the small opening of the Xpert Flu Assay Cartridge. The GeneXpert Cartridge is loaded onto the GeneXpert® Instrument System platform, which performs hands-off automated sample processing and real-time PCR for detection of Flu RNA. Summary and detailed test results are obtained in 75 minutes.
The results are interpolated by the GeneXpert Instrument Systems software from measured fluorescent signals and embedded calculation algorithms and are shown in the "View Results" window in tabular and graphic formats. The Xpert Flu Assay provides test results for influenza A, influenza B and influenza A, subtype 2009 H1N1. It also reports if the test is "Invalid," "Error" or "No Result," and instructs the user to repeat the test.
Here's an analysis of the acceptance criteria and study detailed in the provided 510(k) summary:
1. Table of Acceptance Criteria and Reported Device Performance
The document describes a reproducibility/precision study conducted to compare the performance of the GeneXpert Dx and the GeneXpert Infinity-80 Instrument Systems. The acceptance criteria are implicitly good agreement between the two systems, with specific percentage agreement targets for different sample types and concentrations.
| Acceptance Criteria (Implied) | Reported Device Performance (GeneXpert Dx / Infinity-80 / % Total Agreement) |
|---|---|
| Negative samples: High agreement (e.g., >95%) | 100.0% / 100.0% / 100.0% |
| Moderate positive samples: High agreement (e.g., >95%) | Flu A: 100.0% / 100.0% / 100.0% |
| 2009 H1N1: 100.0% / 100.0% / 100.0% | |
| Flu B: 97.9% / 100.0% / 99.0% | |
| Low positive samples: High agreement (e.g., >90%) | Flu A: 97.9% / 99.0% / 98.4% |
| 2009 H1N1: 97.9% / 99.0% / 98.4% | |
| Flu B: 81.3% / 88.5% / 84.9% | |
| High negative samples: Acceptable agreement (e.g., >80%) | Flu A: 93.8% / 87.5% / 90.6% |
| 2009 H1N1: 54.2% / 38.7% / 46.6% | |
| Flu B: 85.4% / 83.3% / 84.4% | |
| Overall agreement: High (e.g., >85%) | 90.8% / 89.8% / 90.3% |
Note: The "high negative" samples, particularly for 2009 H1N1 and Flu B, show lower agreement percentages. This is often expected for samples around the limit of detection, where results can fluctuate more. The study's conclusion that "The two Instrument Systems were shown to provide comparable results" indicates these levels were deemed acceptable for the purpose of demonstrating substantial equivalence of the new instrument system.
2. Sample Size Used for the Test Set and Data Provenance
- Test Set Sample Size: The study used a panel of 10 specimens (with varying concentrations of influenza A, B, and 2009 H1N1). Each specimen was tested:
- 4 times per day
- for 12 days
- by 2 operators
- on 2 instrument systems (GeneXpert Dx and GeneXpert Infinity-80).
- This results in (4 * 12 * 2 * 2 = 192) individual tests per specimen type, or 192 total tests for each specific sample ID category (e.g., 192 tests for "Negative", 192 tests for "Flu A moderate positive", etc.).
- For the "2009 H1N1 high negative" sample on the Infinity-80, 3 out of 96 samples yielded indeterminate results on both attempts, reducing the effective sample size to 93 (93/96) for that specific comparison.
- Data Provenance: Not explicitly stated. The study was conducted by Cepheid, indicating it's likely internal analytical data, not from a specific country or clinical setting. It is a prospective analytical study designed for reproducibility/precision testing.
3. Number of Experts Used to Establish the Ground Truth for the Test Set and Their Qualifications
- Ground Truth Experts: The document does not mention the use of experts to establish the ground truth for these analytical samples. The samples were prepared as "Negative," "moderate positive," "low positive," and "high negative" concentrations of known viral targets. This suggests the "ground truth" was established based on the known composition and concentration of the prepared panel specimens themselves, rather than clinical adjudication by experts.
- Qualifications: Not applicable, as expert adjudication was not used for this analytical study.
4. Adjudication Method for the Test Set
- Adjudication Method: Not applicable. The "ground truth" for the analytical samples was determined by their known viral content and concentration as prepared by the manufacturer for the study. The study's purpose was to compare agreement between two instrument systems for these known samples, not to
adjudicate ambiguous clinical results.
5. If a Multi-Reader Multi-Case (MRMC) Comparative Effectiveness Study Was Done
- MRMC Study: No, an MRMC comparative effectiveness study was not done. This study solely focused on the analytical performance (reproducibility/precision) of the device across different instrument platforms. It did not involve human readers interpreting results, nor did it measure the effect size of human readers with or without AI assistance.
6. If a Standalone (Algorithm Only Without Human-in-the-Loop Performance) Was Done
- Standalone Performance: Yes, this study effectively represents a standalone performance evaluation of the integrated system (instrument + assay + embedded software). The results are generated automatically by the GeneXpert Instrument Systems software from measured fluorescent signals and embedded calculation algorithms. Human intervention is limited to specimen preparation and loading the cartridge.
7. The Type of Ground Truth Used
- Type of Ground Truth: The ground truth for the test set was based on prepared samples with known concentrations of viral RNA. These were spiked or formulated samples to represent negative, moderate positive, low positive, and high negative (near limit of detection) states for influenza A, B, and 2009 H1N1.
8. The Sample Size for the Training Set
- Training Set Sample Size: The document does not provide information on the training set sample size. This 510(k) submission is for a modification to an existing device (Xpert Flu Assay, predicate device K103766) to add a new instrument system (GeneXpert Infinity-80). It is highly likely that the original predicate device was developed and cleared with extensive training data, but that information is not part of this specific submission's summary for the modification.
9. How the Ground Truth for the Training Set Was Established
- Training Set Ground Truth: The document does not provide information on how the ground truth for the training set was established. As with the training set sample size, this information would likely be found in the original 510(k) submission for the predicate device (K103766).
§ 866.3332 Reagents for detection of specific novel influenza A viruses.
(a)
Identification. Reagents for detection of specific novel influenza A viruses are devices that are intended for use in a nucleic acid amplification test to directly detect specific virus RNA in human respiratory specimens or viral cultures. Detection of specific virus RNA aids in the diagnosis of influenza caused by specific novel influenza A viruses in patients with clinical risk of infection with these viruses, and also aids in the presumptive laboratory identification of specific novel influenza A viruses to provide epidemiological information on influenza. These reagents include primers, probes, and specific influenza A virus controls.(b)
Classification. Class II (special controls). The special controls are:(1) FDA's guidance document entitled “Class II Special Controls Guidance Document: Reagents for Detection of Specific Novel Influenza A Viruses.” See § 866.1(e) for information on obtaining this document.
(2) The distribution of these devices is limited to laboratories with experienced personnel who have training in standardized molecular testing procedures and expertise in viral diagnosis, and appropriate biosafety equipment and containment.