(82 days)
The Cepheid Xpert Norovirus Assay, performed on the GeneXpert® Instrument Systems, is a qualitative in vitro diagnostic test for the identification and differentiation of norovirus genogroup I and genogroup II RNA from raw or unpreserved unformed stool specimens collected from individuals with symptoms of acute gastroenteritis. The test utilizes automated real-time reverse transcriptase polymerase chain reaction (RT-PCR) to detect norovirus RNA. The Xpert Norovirus Assay is intended to aid in the diagnosis of norovirus infections when used in conjunction with clinical evaluation, laboratory findings, and epidemiological information. The assay also aids in the detection and identification of norovirus infections in the context of outbreaks.
The Xpert Norovirus Assay is an automated in vitro diagnostic test for detection and differentiation of nucleic acid sequences for norovirus genogroup I and genogroup II from raw or unpreserved unformed (liquid or soft) stool specimens collected from individuals with symptoms of acute gastroenteritis. The test utilizes automated, multiplex real-time, reverse transcriptase polymerase chain reaction (RT-PCR) to detect specific viral gene sequences associated with norovirus genogroup I and genogroup II. The Xpert Norovirus Assay is intended to aid in the diagnosis of norovirus infections when used in conjunction with clinical evaluation, laboratory findings, and epidemiological information. The assay also aids in the detection and identification of norovirus infections in the context of outbreaks.
The Xpert Norovirus Assay is performed on the Cepheid GeneXpert Instrument Systems (GeneXpert Dx, GeneXpert Infinity-48, GeneXpert Infinity-48s, and GeneXpert Infinity-80 systems). The GeneXpert Instrument System platform automates sample preparation, amplification and real-time detection.
The GeneXpert Instrument Systems require the use of single-use, disposable cartridges (the Xpert Norovirus 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 Norovirus Assay includes reagents for the detection and differentiation of nucleic acid sequences for norovirus genogroup I and genogroup II from raw or unpreserved unformed human stool specimens collected from patients with signs and symptoms of acute gastroenteritis. All reagents except the Sample Reagent are contained pre-loaded in the cartridge. A Sample Processing Control (SPC) and a Probe Check Control (PCC) are also included in the cartridge. 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 single-use, multi-chambered fluidic cartridges are designed to complete sample preparation and real-time RT-PCR for detection and differentiation of norovirus genogroup I and genogroup II viral RNA in 90 minutes or less. The GeneXpert Instrument Systems, comprised of the GeneXpert Dx Systems and the GeneXpert Infinity Systems, have 1 to 80 randomly accessible modules, depending upon the instrument, that are each capable of performing separate sample preparation and real-time PCR and RT-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 RT-PCR and detection.
Specimens are collected following the user's institution standard procedures for collecting stool specimens for norovirus testing and sent to the GeneXpert® testing area for processing. The specimen may be stored at 2-8 ℃ for up to two days prior to processing. When ready to process the specimen, a single-use disposable dry swab is used for transfer of the stool specimen to the Sample Reagent bottle that is provided with the Xpert Norovirus Assay kit. The user vortexes the capped Sample Reagent bottle for 10 seconds and transfers the entire contents to the sample chamber in the top of the disposable fluidic cartridge with a transfer pipette. The user initiates a test from the system user interface and places the cartridge into the GeneXpert instrument platform, which performs hands-off real-time, multiplex polymerase chain reaction (PCR) for detection of RNA. The results are automatically generated at the end of the process in a report that can be viewed and printed.
The document describes the Xpert Norovirus Assay, a qualitative in vitro diagnostic test for norovirus genogroup I and genogroup II RNA in stool specimens.
Here's an analysis of the acceptance criteria and the study that proves the device meets them:
1. A table of acceptance criteria and the reported device performance
The document does not explicitly state "acceptance criteria" for the clinical performance in a singular, consolidated table with pass/fail thresholds. Instead, it provides the observed performance metrics (PPA, NPA) with 95% confidence intervals from a clinical study, implying that these values were considered acceptable by the FDA for substantial equivalence. For analytical performance (LoD, specificity), the values obtained are presented as the device's performance without explicit numerical targets being stated beforehand.
Below is a table summarizing the reported device performance, with implied acceptance based on FDA clearance.
| Test Parameter / Criteria | Acceptance Criteria (Implied) | Reported Device Performance (Xpert Norovirus Assay) |
|---|---|---|
| Analytical Performance | ||
| Limit of Detection (LoD) Norovirus GI.3 | Reproducibly distinguished from negative samples with 95% confidence | 5.7 x 105 copies/mL (95% CI: 4.64 x 105 – 6.67 x 105) |
| Limit of Detection (LoD) Norovirus GII.4 | Reproducibly distinguished from negative samples with 95% confidence | 3.0 x 105 copies/mL (95% CI: 1.25 x 105 – 1.78 x 105) |
| Analytical Specificity (Cross-reactivity) | 100% specificity (no false positives for other organisms) | 100% (All 68 organisms tested were correctly reported as NORO GI NOT DETECTED; NORO GII NOT DETECTED) |
| Analytical Reactivity (Inclusivity) | Detect all 31 tested norovirus genotypes (GI and GII) | All 31 norovirus strains (representing GI and GII genotypes) tested near LoD concentration resulted in POS for the correct genogroup and NEG for the other. |
| Potential Interfering Substances (Inhibition/False-Negatives) | No significant inhibition or false negatives | Inhibition observed with Benzalkonium chloride (1% w/v, 0.2% w/v, 0.04% w/v), false negatives for Norovirus GII at 1% w/v. Statistically significant inhibitory effect on Norovirus GII Ct with Barium sulfate (5% w/w). No other substances found inhibitory or causing false negatives. (Note: These are findings, not direct "pass" criteria, but inform proper use instructions). |
| Carry-Over Contamination | No carry-over contamination | 19/20 positive samples correctly detected, 1 reported as ERROR. All 22 negative samples correctly reported. (Demonstrates acceptable control of carry-over for the claimed self-contained system). |
| Clinical Performance (Fresh, Prospective Specimens) | ||
| Norovirus GI: Positive Percent Agreement (PPA) | Sufficiently high agreement with reference method | 100% (95% CI: 73.5-100) |
| Norovirus GI: Negative Percent Agreement (NPA) | Sufficiently high agreement with reference method | 99.6% (95% CI: 98.9-99.9) |
| Norovirus GII: Positive Percent Agreement (PPA) | Sufficiently high agreement with reference method | 98.5% (95% CI: 91.7-100) |
| Norovirus GII: Negative Percent Agreement (NPA) | Sufficiently high agreement with reference method | 98.8% (95% CI: 97.8-99.4) |
| Clinical Performance (Frozen, Archived Specimens) | ||
| Norovirus GI: Positive Percent Agreement (PPA) | Sufficiently high agreement with reference method | 98.1% (95% CI: 93.2-99.8) |
| Norovirus GI: Negative Percent Agreement (NPA) | Sufficiently high agreement with reference method | 94.6% (95% CI: 91.8-96.6) |
| Norovirus GII: Positive Percent Agreement (PPA) | Sufficiently high agreement with reference method | 100% (95% CI: 96.7-100) |
| Norovirus GII: Negative Percent Agreement (NPA) | Sufficiently high agreement with reference method | 96.8% (95% CI: 94.5-98.3) |
| Reproducibility | High agreement between sites, days, operators | Overall agreement for Neg (100%), GI-Low Pos (93.3%), GI-Mod Pos (100%), GII-Low Pos (95.0%), GII-Mod Pos (98.3%). High Neg samples showed lower agreement (GI: 25.0%, GII: 30.0%) as expected due to being near LoD. Ct values showed low CVs across sites, days, and operators. |
| Instrument System Precision | High agreement between GeneXpert Dx and Infinity systems | Overall agreement for Neg (100%), GI-Low Pos (98.4%), GI-Mod Pos (100%), GII-Low Pos (88.5%), GII-Mod Pos (100%). High Neg samples showed lower agreement (GI: 16.2%, GII: 28.7%). Ct values showed low CVs across instruments, lots, days, and operators. |
2. Sample size used for the test set and the data provenance (e.g. country of origin of the data, retrospective or prospective)
- Clinical Study Test Set Sample Size:
- Norovirus GI: 1403 total specimens (914 fresh, prospectively collected; 489 frozen, archived).
- Norovirus GII: 1401 total specimens (914 fresh, prospectively collected; 487 frozen, archived).
- Data Provenance:
- Origin: The clinical studies were evaluated at seven institutions in the U.S. and the E.U.
- Retrospective or Prospective:
- Prospective: 914 fresh, prospectively collected specimens.
- Retrospective (Archived): 489 frozen, archived specimens for GI and 487 for GII.
3. Number of experts used to establish the ground truth for the test set and the qualifications of those experts (e.g. radiologist with 10 years of experience)
The document states that the performance of the Xpert Norovirus Assay was compared to a composite reference test method performed at the CDC (Atlanta, GA). It does not specify the number of individual experts, their specific qualifications (e.g., radiologist with 10 years of experience), or if multiple experts were involved in interpreting the results of the composite reference test. The "composite reference test" itself acts as the ground truth.
4. Adjudication method (e.g. 2+1, 3+1, none) for the test set
The document does not describe an explicit adjudication method (like 2+1 or 3+1) involving multiple human readers for establishing the ground truth. The ground truth was established by a "composite comparator method that consisted of a combination of Center for Disease Control and Prevention (CDC) RT-PCR assays and bi-directional sequencing for norovirus". This implies a definitive laboratory-based method rather than a consensus among human interpreters.
5. If a multi-reader multi-case (MRMC) comparative effectiveness study was done, If so, what was the effect size of how much human readers improve with AI vs without AI assistance
No, a multi-reader multi-case (MRMC) comparative effectiveness study was not performed. This device is a diagnostic assay (an in-vitro diagnostic test), not an AI-assisted imaging device or a decision support system for human readers. Therefore, the concept of "human readers improve with AI vs without AI assistance" is not applicable to this submission.
6. If a standalone (i.e. algorithm only without human-in-the-loop performance) was done
Yes, the primary clinical performance evaluation (PPA and NPA) presented for the Xpert Norovirus Assay is a standalone (algorithm only) performance measure. The assay processes the sample and provides a result ("NORO GI DETECTED," "NORO GII DETECTED," or "NOT DETECTED") without human interpretive input into the test result itself. The test is stated to be "intended to aid in the diagnosis... when used in conjunction with clinical evaluation, laboratory findings, and epidemiological information," implying that clinicians use the standalone result in their overall patient management, but the device performance metrics themselves are standalone.
7. The type of ground truth used (expert consensus, pathology, outcomes data, etc.)
The ground truth used was a composite reference method. Specifically, it consisted of:
- Center for Disease Control and Prevention (CDC) RT-PCR assays
- Bi-directional sequencing for norovirus
This is a laboratory-based, molecular diagnostic ground truth, considered highly authoritative for viral detection.
8. The sample size for the training set
This document describes a premarket notification for an IVD device, which typically involves analytical and clinical verification/validation studies. It does not explicitly mention a "training set" in the context of machine learning, as the device is a molecular diagnostic assay based on RT-PCR, not an AI/ML algorithm that requires training data in the same way. The studies outlined are for evaluating the device's performance against established methods.
9. How the ground truth for the training set was established
As there is no "training set" described for a machine learning algorithm, this question is not applicable in the context of this IVD device submission. The described studies are validation studies against a composite reference method.
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Food and Drug Administration 10903 New Hampshire Avenue Document Control Center - WO66-G609 Silver Spring, MD 20993-0002
Cepheid Scott Campbell, Ph.D., MBA Executive Director, Clinical Affairs 904 Caribbean Drive Sunnyvale CA 94089-1189
November 26, 2014
Re: K142501
Trade/Device Name: Xpert® Norovirus Regulation Number: 21 CFR 866.3990 Regulation Name: Gastrointestinal Microorganism Multiplex Nucleic Acid-Based Assay Regulatory Class: II Product Code: PIO. OOI Dated: September 4, 2014 Received: September 5, 2014
Dear Dr. Campbell:
We have reviewed your Section 510(k) premarket notification of intent to market the device referenced above and have determined the device is substantially equivalent (for the indications for use stated in the enclosure) to legally marketed predicate devices marketed in interstate commerce prior to May 28, 1976, the enactment date of the Medical Device Amendments, or to devices that have been reclassified in accordance with the provisions of the Federal Food. Drug. and Cosmetic Act (Act) that do not require approval of a premarket approval application (PMA). You may, therefore, market the device, subject to the general controls provisions of the Act. The general controls provisions of the Act include requirements for annual registration, listing of devices, good manufacturing practice, labeling, and prohibitions against misbranding and adulteration. Please note: CDRH does not evaluate information related to contract liability warranties. We remind you, however, that device labeling must be truthful and not misleading.
If your device is classified (see above) into either class II (Special Controls) or class III (PMA), it may be subject to additional controls. Existing major regulations affecting your device can be found in the Code of Federal Regulations, Title 21. Parts 800 to 898. In addition, FDA may publish further announcements concerning your device in the Federal Register.
Please be advised that FDA's issuance of a substantial equivalence determination does not mean that FDA has made a determination that your device complies with other requirements of the Act or any Federal statutes and regulations administered by other Federal agencies. You must comply with all the Act's requirements, including, but not limited to: registration and listing (21 CFR Part 807); labeling (21 CFR Parts 801 and 809); medical device reporting (reporting of medical device-related adverse events) (21 CFR 803); good manufacturing practice requirements as set forth in the quality systems (QS) regulation (21 CFR Part 820); and if applicable, the electronic product radiation control provisions (Sections 531-542 of the Act); 21 CFR 1000-1050.
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If you desire specific advice for your device on our labeling regulations (21 CFR Parts 801 and 809), please contact the Division of Industry and Consumer Education at its toll-free number (800) 638 2041 or (301) 796-7100 or at its Internet address
http://www.fda.gov/MedicalDevices/Resourcesfor You/Industry/default.htm. Also, please note the regulation entitled, "Misbranding by reference to premarket notification" (21 CFR Part 807.97). For questions regarding the reporting of adverse events under the MDR regulation (21 CFR Part 803), please go to
http://www.fda.gov/MedicalDevices/Safety/ReportaProblem/default.htm for the CDRH's Office of Surveillance and Biometrics/Division of Postmarket Surveillance.
You may obtain other general information on your responsibilities under the Act from the Division of Industry and Consumer Education at its toll-free number (800) 638-2041 or (301) 796-7100 or at its Internet address
http://www.fda.gov/MedicalDevices/ResourcesforYou/Industry/default.htm.
Sincerely yours.
Uwe Scherf -S for
Sally A. Hojvat, M. Sc., Ph.D. Director Division of Microbiology Devices Office of In Vitro Diagnostics and Radiological Health Center for Devices and Radiological Health
Enclosure
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Indications for Use
510(k) Number (if known) K142501
Device Name Xpert Norovirus
Indications for Use (Describe)
The Cepheid Xpert Norovirus Assay, performed on the GeneXpert® Instrument Systems, is a qualitative in vitro diagnostic test for the identification and differentiation of norovirus genogroup I and genogroup II RNA from raw or unpreserved unformed stool specimens collected from individuals with symptoms of acute gastroenteritis. The test utilizes automated real-time reverse transcriptase polymerase chain reaction (RT-PCR) to detect norovirus RNA. The Xpert Norovirus Assay is intended to aid in the diagnosis of norovirus infections when used in conjunction with clinical evaluation, laboratory findings, and epidemiological information. The assay also aids in the detection and identification of norovirus infections in the context of outbreaks.
Type of Use (Select one or both, as applicable)
2 Prescription Use (Part 21 CFR 801 Subpart D)
_ Over-The-Counter Use (21 CFR 801 Subpart C)
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510(k) Summary
As required by 21 CFR Section 807.92(c).
| Submitted by: | Cepheid904 Caribbean DriveSunnyvale, CA 90489Phone number: (408) 400-8460Fax number: (847) 510-0539 |
|---|---|
| Contact: | Kerry J. Flom, Ph.D. |
| Date of Preparation: | October 28, 2014 |
| Device: | |
| Trade name: | Xpert® Norovirus |
| Common name: | Xpert Norovirus Assay |
| Type of Test: | Automated real-time reverse transcription-polymerase chainreaction (RT-PCR) assay intended for the in vitro qualitativedetection and differentiation of norovirus genogroup I andgenogroup II RNA. |
| Regulation number/Classification name/Product code: | 866.3990/Gastrointestinal pathogen panel multiplex nucleicacid-based assay system /PIQInstrumentation for clinical multiplex test systems/OOI |
| ClassificationAdvisory Panel | Microbiology (83) |
| Prescription Use | Yes |
| Predicate DevicesName(s): | Luminex Molecular Diagnostics, Inc., xTAG®Gastrointestinal Pathogen Panel (GPP) (510(k) #K121894) |
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Device Description:
The Xpert Norovirus Assay is an automated in vitro diagnostic test for detection and differentiation of nucleic acid sequences for norovirus genogroup I and genogroup II from raw or unpreserved unformed (liquid or soft) stool specimens collected from individuals with symptoms of acute gastroenteritis. The test utilizes automated, multiplex real-time, reverse transcriptase polymerase chain reaction (RT-PCR) to detect specific viral gene sequences associated with norovirus genogroup I and genogroup II. The Xpert Norovirus Assay is intended to aid in the diagnosis of norovirus infections when used in conjunction with clinical evaluation, laboratory findings, and epidemiological information. The assay also aids in the detection and identification of norovirus infections in the context of outbreaks.
The Xpert Norovirus Assay is performed on the Cepheid GeneXpert Instrument Systems (GeneXpert Dx, GeneXpert Infinity-48, GeneXpert Infinity-48s, and GeneXpert Infinity-80 systems). The GeneXpert Instrument System platform automates sample preparation, amplification and real-time detection.
The GeneXpert Instrument Systems require the use of single-use, disposable cartridges (the Xpert Norovirus 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 Norovirus Assay includes reagents for the detection and differentiation of nucleic acid sequences for norovirus genogroup I and genogroup II from raw or unpreserved unformed human stool specimens collected from patients with signs and symptoms of acute gastroenteritis. All reagents except the Sample Reagent are contained pre-loaded in the cartridge. A Sample Processing Control (SPC) and a Probe Check Control (PCC) are also included in the cartridge. 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 single-use, multi-chambered fluidic cartridges are designed to complete sample preparation and real-time RT-PCR for detection and differentiation of norovirus genogroup I and genogroup II viral RNA in 90 minutes or less. The GeneXpert Instrument Systems, comprised of the GeneXpert Dx Systems and the GeneXpert Infinity Systems, have 1 to 80 randomly accessible modules, depending upon the instrument, that are each capable of performing separate sample preparation and real-time PCR and RT-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
1 Although sonication is a fundamental capability of every GeneXpert module, sonication is not used in the Xpert Norovirus Assay.
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proprietary I-CORE® thermocycler for performing real-time PCR and RT-PCR and detection.
Specimens are collected following the user's institution standard procedures for collecting stool specimens for norovirus testing and sent to the GeneXpert® testing area for processing. The specimen may be stored at 2-8 ℃ for up to two days prior to processing. When ready to process the specimen, a single-use disposable dry swab is used for transfer of the stool specimen to the Sample Reagent bottle that is provided with the Xpert Norovirus Assay kit. The user vortexes the capped Sample Reagent bottle for 10 seconds and transfers the entire contents to the sample chamber in the top of the disposable fluidic cartridge with a transfer pipette. The user initiates a test from the system user interface and places the cartridge into the GeneXpert instrument platform, which performs hands-off real-time, multiplex polymerase chain reaction (PCR) for detection of RNA. The results are automatically generated at the end of the process in a report that can be viewed and printed.
Device Intended Use:
The Cepheid Xpert Norovirus Assay, performed on the GeneXpert® Instrument Systems, is a qualitative in vitro diagnostic test for the identification and differentiation of norovirus genogroup I and genogroup II RNA from raw or unpreserved unformed stool specimens collected from individuals with symptoms of acute gastroenteritis. The test utilizes automated real-time reverse transcriptase polymerase chain reaction (RT-PCR) to detect norovirus RNA. The Xpert Norovirus Assay is intended to aid in the diagnosis of norovirus infections when used in conjunction with clinical evaluation, laboratory findings, and epidemiological information. The assay also aids in the detection and identification of norovirus infections in the context of outbreaks.
Substantial Equivalence:
The Xpert Norovirus Assay is substantially equivalent to the Luminex Molecular Diagnostics, Inc., xTAG® Gastrointestinal Pathogen Panel (Luminex xTAG GPP) [510(k) #K121894]. The Xpert Norovirus Assay and the Luminex xTAG GPP both detect norovirus genogroup I and genogroup II from human stool specimens using multiplex nucleic acid-based technology. A multi-center clinical study was conducted to determine the performance characteristics of the Xpert Norovirus Assay relative to a composite comparator method that consisted of a combination of Center for Disease Control and Prevention (CDC) RT-PCR assays and bi-directional sequencing for norovirus. The Luminex xTAG GPP used the same composite comparator method in a clinical study to determine its performance characteristics. The Xpert Norovirus Assay study results showed the Xpert Norovirus Assay is acceptable for its intended use and is as safe and effective as the predicate device.
Table 5-1 shows the similarities and differences between the Xpert Norovirus Assay and the predicate device.
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| Similarities | ||
|---|---|---|
| Device | Predicate Device | |
| Item | Xpert Norovirus (K142501) | Luminex xTAG GPP (K121894) |
| Regulation | 21 CFR 866.3990 | 21 CFR 866.3990 |
| DeviceClass | Class II | Class II |
| TechnologyPrinciple ofOperation | Real-time reverse transcriptasepolymerase chain reaction (RT-PCR) | Real-time reverse transcriptasepolymerase chain reaction (RT-PCR) |
| GeneralIntendedUse | The Cepheid Xpert Norovirus Assay,performed on the GeneXpert®Instrument Systems, is a qualitativein vitro diagnostic test for theidentification and differentiation ofnorovirus genogroup I and genogroupII RNA from raw or unpreservedunformed stool specimens collectedfrom individuals with symptoms ofacute gastroenteritis. The test utilizesautomated real-time reversetranscriptase polymerase chainreaction (RT-PCR) to detectnorovirus RNA. The XpertNorovirus Assay is intended to aid inthe diagnosis of norovirus infectionswhen used in conjunction withclinical evaluation, laboratoryfindings, and epidemiologicalinformation. The assay also aids inthe detection and identification ofnorovirus infections in the context ofoutbreaks. | The xTAG®Gastrointestinal PathogenPanel (GPP) is a multiplexed nucleicacid test intended for the simultaneousqualitative detection and identificationof multiple viral, parasitic, andbacterial nucleic acids in human stoolspecimens from individuals with signsand symptoms of infectious colitis orgastroenteritis. The following pathogentypes, subtypes and toxin genes areidentified using the xTAG® GPP:• Campylobacter ( C. jejuni, C. coliand C. lari only)• Clostridium difficile ( C. difficile )toxin A/B• Cryptosporidium ( C. parvum and C. hominis only)• Escherichia coli ( E. coli ) 0157• Enterotoxigenic Escherichia coli(ETEC) LT/ST• Giardia ( G. lamblia only - alsoknown as G. intestinalis and G. duodenalis )• Norovirus GI/GII• Rotavirus A• Salmonella• Shiga-like Toxin producing E. coli(STEC) stx 1/stx 2• Shigella ( S. boydii, S. sonnei, S. flexneri and S. dysenteriae )The detection and identification of |
| Similarities | ||
| Device | Predicate Device | |
| Item | Xpert Norovirus (K142501) | Luminex xTAG GPP (K121894) |
| specific gastrointestinal microbialnucleic acid from individualsexhibiting signs and symptoms ofgastrointestinal infection aids in thediagnosis of gastrointestinal infectionwhen used in conjunction with clinicalevaluation, laboratory findings andepidemiological information. Agastrointestinal microorganismmultiplex nucleic acid-based assay alsoaids in the detection and identificationof acute gastroenteritis in the contextof outbreaks. | ||
| xTAG® GPP positive results arepresumptive and must be confirmedby FDA-cleared tests or otheracceptable reference methods. | ||
| The results of this test should not beused as the sole basis for diagnosis,treatment, or other patient managementdecisions. Confirmed positive resultsdo not rule out co-infection with otherorganisms that are not detected by thistest, and may not be the sole ordefinitive cause of patient illness.Negative xTAGGastrointestinalPathogen Panel results in the setting ofclinical illness compatible withgastroenteritis may be due to infectionby pathogens that are not detected bythis test or non-infectious causes suchas ulcerative colitis, irritable bowelsyndrome, or Crohn's disease. | ||
| xTAG® GPP is not intended tomonitor or guide treatment for C.difficile infections. | ||
| The xTAG® GPP is indicated for usewith the Luminex® MAGPIX®instrument. | ||
| Similarities | ||
| Device | Predicate Device | |
| Item | Xpert Norovirus (K142501) | Luminex xTAG GPP (K121894) |
| SpecimenTypes | Human stool | Human stool |
| Differences | ||
| New Device | Predicate Device | |
| Item | Xpert Norovirus (K142501) | Luminex xTAG GPP (K121894) |
| ProductCode | PIQ | PCH |
| AssayResults | Qualitative detection of NorovirusGI/GII | Qualitative detection of norovirus |
| AnalyteDetected | Detects and differentiates betweenNorovirus GI/GII. | Detects norovirus but does notdifferentiate between NorovirusGI/GII. |
| TechnologyPrinciples ofOperation | Amplification: multiplex real-timeRT-PCRDetection: fluorogenic target-specific hybridization | Multiplex RT-PCR and multiplexTarget Specific Primer Extensionfollowed by Fluorescence-activatedsorting of labeled beads coupled tostreptavidin-conjugated biotinylatedproducts. |
| Sample Pre-treatment | Place swab dipped in specimen intoprovided tube of sample reagent.Vortex 10 seconds. | 30-45 minutes of manual sample pre-treatment preparation. |
| NucleicAcidIsolationandpurification | Self-contained and automated in theGeneXpert Cartridge and GeneXpertInstrument Systems. No reagentpreparation - all reagents arecontained in the cartridge. | Multi-step manual reagentpreparation for use withNucliSENS® EasyMAG extractionKit (BioMerieux). |
| InstrumentSystems | Cepheid GeneXpert Dx Systems andGeneXpert Infinity Systems | Nucleic Acid Purification SystemPCR ThermocyclerLuminex® 100/200® or MAGPIX®instruments |
Table 5-1: Comparison of Similarities and Differences of the
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| Differences | ||
|---|---|---|
| New Device | Predicate Device | |
| Item | Xpert Norovirus (K142501) | Luminex xTAG GPP (K121894) |
| InternalControls | Sample processing control (SPC)and probe check control (PCC)integrated in assay/instrumentsystem.External controls available but notprovided. | Internal control added to eachsample. External control processedwith each batch of samples. |
| Time toobtain testresults | Test results: 90 minutes or less forsample preparation and RT-PCR. | Test results in <5 hours, not including30-45 minute sample pre-treatment. |
Analytical Performance:
Analytical Sensitivity (Limit of Detection)
The limit of detection (LoD) study was performed to evaluate the analytical sensitivity of the Xpert Norovirus Assay with positive clinical stool specimens containing Norovirus GI.3 or Norovirus GII.4 diluted into a pooled negative stool matrix. The LoD is defined as the lowest concentration (copies/mL) per sample that can be reproducibly distinguished from negative samples with 95% confidence. Replicates of at least 23 were evaluated at seven concentrations for Norovirus GI.3 and Norovirus GII.4 and LoDs were estimated by probit analysis. The estimated LoDs were confirmed by testing at least 20 replicate samples with virus diluted to the estimated LoD concentrations.
The LoD point estimates and confirmed LoD for each genogroup tested are summarized in Table 5-2.
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| NorovirusGenogroup/strain | Limit of Detection(95% CI) |
|---|---|
| GI.3 | 5.7 x 105(copies/mL)(4.64 x 105 – 6.67 x 105) |
| GII.4 | 3.0 x 105 (copies/mL)(1.25 x 105 – 1.78 x 105) |
Table 5-2: Limit of Detection of the Xpert Norovirus Assay
Analytical Specificity (Cross-reactivity)
The analytical specificity of the Xpert Norovirus Assay was evaluated by testing a panel of 68 organisms, consisting of 54 bacteria, 1 fungi, 9 viruses, and 4 parasites representing common gastroenteritis pathogens or those potentially encountered in stool. A minimum of three replicates of all bacterial and fungal strains were tested at concentrations ≥ 10° CFU/mL. A minimum of three replicates of all viruses were tested at concentrations ≥ 10 TCID50/mL with the exception of two viruses obtained from clinical samples with unknown concentrations. A minimum of three replicates of all parasites were tested at concentrations ≥ 10° copies/mL. All organisms tested were correctly reported as NORO GI NOT DETECTED; NORO GII NOT DETECTED by the Xpert Norovirus Assay. The analytical specificity was 100%. Results are shown in Table 5-3.
| Organism | Strain ID | Concentration |
|---|---|---|
| Acinetobacter baumannii | CCUG 3477 | >3.0 x 108 CFU/mL |
| Anaerococcus prevotiia | ATCC 9321 | 6.7 x 108 CFU/mL |
| Bacteriocides fragilisa | ATCC 25285 | 1.4 x 109 CFU/mL |
| Campylobacter coli | ATCC 43478 | 1.8 x 108 CFU/mL |
| Campylobacter jejuni | ATCC 33560 | 1.3 x 108 CFU/mL |
| Campylobacter lari | ATCC 35221 | 3.4 x 107 CFU/mL |
| Citrobacter freundii | ATCC 33128 | 1.5 x 109 CFU/mL |
| Clostridium difficilea | ATCC 9689 | 2.2 x 108 CFU/mL |
| Organism | Strain ID | Concentration |
| Clostridium sordellia | DSMZ 2141 | 2.0 x 108 CFU/mL |
| Eggerthella lenta | ATCC 43055 | >3.0 x 107 CFU/mL |
| Enterobacter cloacae | ATCC 70021 | 1.0 x 109 CFU/mL |
| Enterococcus casseliflavus | ATCC 25788 | 1.0 x 109 CFU/mL |
| Enterococcus faecalis | ATCC 29212 | 5.4 x 108 CFU/mL |
| Enterococcus faecium | ATCC 9756 | 8.2 x 108 CFU/mL |
| Enterococcus gallinarium | ATCC 49573 | 4.5 x 108 CFU/mL |
| Escherichia coli O157:H7 | ATCC 43888 | 8.4 x 108 CFU/mL |
| Escherichia coli O26:H11 | CDC 033014 | 7.4 x 108 CFU/mL |
| Escherichia coli O45:H2 | CDC 003039 | 3.3 x 108 CFU/mL |
| Escherichia coli O103:H11 | CDC 063008 | 5.4 x 108 CFU/mL |
| Escherichia coli 011 | CDC 201114 | 6.9 x 108 CFU/mL |
| Escherichia coli 0121 | CDC 023211 | 1.4 x 109 CFU/mL |
| Escherichia coli 0145 | CDC 993311 | 7.1 x 108 CFU/mL |
| Escherichia hermannii | ATCC 33650 | 1.5 x 109 CFU/mL |
| Fusobacterium necrophoruma | ATCC 31647 | 9.6 x 108 CFU/mL |
| Helicobacter pylori | CCUG 1784 | 1.5 x 108 CFU/mL |
| Klebsiella pneumoniae | ATCC 70063 | 1.2 x 109 CFU/mL |
| Lactobacillus jensenii | ATCC 25258 | 4.0 x 108 CFU/mL |
| Listeria monocytogenes | CCUG 3358 | 1.2 x 109 CFU/mL |
| Micrococcus luteus | ATCC 4698 | 1.8 x 108 CFU/mL |
| Morganella morganii | ATCC 49948 | 1.3x109 CFU/mL |
| Peptostreptococcusanaerobiusa | CCUG 7835 | 1.5 x 109 CFU/mL |
| Plesiomonas shigelloides | ATCC 51903 | 3.1 x 108 CFU/mL |
| Prevotella oralisa | ATCC 33269 | 1.2 x 109 CFU/mL |
| Proteus mirabilis | ATCC 43071 | 1.1 x 109 CFU/mL |
| Proteus vulgaris | ATCC 49132 | 1.8 x 109 CFU/mL |
| Providencia alcalifaciens | CCUG 6325 | 1.8 x 109 CFU/mL |
| Providencia stuartii | ATCC 49809 | 1.3 x 109 CFU/mL |
| Organism | Strain ID | Concentration |
| Pseudomonas aeruginosa | ATCC 27853 | 6.3 x 108 CFU/mL |
| Pseudomonas fluorescens | ATCC 13525 | >3.0 x 108 CFU/mL |
| Pseudomonas putida | ATCC 49128 | 5.5 x 108 CFU/mL |
| Salmonella agona | ATCC 51957 | 1.2 x 109 CFU/mL |
| Salmonella bongori | ATCC 43975 | 1.7 x 109 CFU/mL |
| Salmonella enterica | ATCC 13314 | 9.2 x 108 CFU/mL |
| Serratia marcescens | ATCC 43862 | 3.8 x 108 CFU/mL |
| Shigella flexneri | ATCC 12022 | 8.1 x 108 CFU/mL |
| Shigella sonnei | ATCC 25931 | >3.0 x 108 CFU/mL |
| Staphylococcus aureus | ATCC 25923 | 8.8 x 108 CFU/mL |
| Staphylococcus epidermidis | ATCC 14990 | >3.0 x 107 CFU/mL |
| Streptococcus agalactiae(GBS) | ATCC 12386 | 9.6 x 108 CFU/mL |
| Streptococcus dysgalactiae | ATCC 43078 | 7.2 x 108 CFU/mL |
| Streptococcus pyogenes | ATCC 19615 | 5.5 x 108 CFU/mL |
| Vibrio choleraeb | CCUG 9118 | 5.2 x 109 copies/µL |
| Vibrio parahaemolyticus | ATCC 17802 | 3.8 x 108 CFU/mL |
| Yersinia enterocolitica | ATCC 9610 | 7.1 x 108 CFU/mL |
| Adenovirus | Type 31 | 3.6 x 105 TCID50/mL |
| Adenovirus | Type 40 | 2.8 x 107 TCID50/mL |
| Adenovirus | Type 41 | 4.6 x 107 TCID50/mL |
| Astrovirusd | -- | Not applicablec |
| Coxsackie virus | Type B5 | 1.4 x 105 TCID50/mL |
| Echovirus | 11 | 3.3 x 109 TCID50/mL |
| Parechovirus | Type 6 | 1.9 x 107 TCID50/mL |
| Rotavirus | Type Wa | 1.0 x 106 TCID50/mL |
| Sapovirusd | -- | Not applicablee |
| Candida albicans | ATCC 10231 | >3.0 x 107 CFU/mL |
| Blastocystis hominisb | BT1 | 1.0 x 109 copies/mL |
| Cryptosporidium parvumb | Iowa | 6.1 x 109 copies/mL |
| Giardia lambliab | Portland-1 | 3.05 x 109 copies/mL |
| Entamoeba histolyticab | ATCC 30459D | 4.9 x 106 copies/mL |
Table 5-3: Analytical Specificity of Xpert Norovirus
{11}------------------------------------------------
{12}------------------------------------------------
Strictly anaerobic bacteria.
b Tested as genomic DNA.
ª Strictly anaerobic bacteria.
° Tested as genomic DNA.
° The concentration is not known for the Astrovirus clinical samples that were obtained from
{13}------------------------------------------------
KUL; the Ct values according to KUL assay were in the range of 12-27. d Clinical sample.
& The concentration is not known for the Sapovirus clinical samples that were obtained from KUL; the Ct values according to KUL assay were in the range of 19-23.
Analytical Reactivity (Inclusivity)
The analytical reactivity of the Xpert Norovirus Assay was evaluated against thirty-one genotypes representing both norovirus genogroups (GI and GII). The thirty-one norovirus strains evaluated in this study were tested near the LoD concentration of the assay (Table 5-4). Three replicates were tested for each strain.
| Norovirus Strain | EstimatedConcentration(copies/mL)a | Result | |
|---|---|---|---|
| GI | GII | ||
| GI.1 | $9.0 x 10^6$ | POS | NEG |
| GI.2 | $3.7 x 10^8$ | POS | NEG |
| GI.3 | $1.4 x 10^6$ | POS | NEG |
| GI.4 | $1.0 x 10^5$ | POS | NEG |
| GI.5b | $2.5 x 10^5$ | POS | NEG |
| GI.6b | $2.5 x 10^5$ | POS | NEG |
| GI.7b | $2.5 x 10^5$ | POS | NEG |
| GI.8 | $3.7 x 10^5$ | POS | NEG |
| GI.14 | $3.0 x 10^6$ | POS | NEG |
| GII.1 | $3.6 x 10^6$ | NEG | POS |
| GII.2 | $1.1 x 10^5$ | NEG | POS |
| GII.3b | $1.3 x 10^3$ | NEG | POS |
| GII.4 (2006a) | $1.2 x 10^5$ | NEG | POS |
| GII.4 (2006b) | $2.4 x 10^5$ | NEG | POS |
| GII.4 (2008) | $4.3 x 10^5$ | NEG | POS |
| GII.4 (2009) New Orleans | $1.7 x 10^5$ | NEG | POS |
| GII.4 (2010) | $9.6 x 10^4$ | NEG | POS |
| GII.4 (2012) Sydney | $1.2 x 10^5$ | NEG | POS |
| GII.5b | $1.3 x 10^3$ | NEG | POS |
| GII.6b | $1.3x 10^3$ | NEG | POS |
| GII.7 | $8.0 x 10^4$ | NEG | POS |
Table 5-4: Analytical Reactivity Results of the Xpert Norovirus Assay
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| Norovirus Strain | EstimatedConcentration(copies/mL)a | Result | |
|---|---|---|---|
| GI | GII | ||
| GII.8b | 1.3 x 103 | NEG | POS |
| GII.9b | 1.3 x 103 | NEG | POS |
| GII.10b | 1.3 x 103 | NEG | POS |
| GII.11 | 2.6 x 105 | NEG | POS |
| GII.12 | 5.7 x 105 | NEG | POS |
| GII.13 | 6.9 x 105 | NEG | POS |
| GII.14 | 1.5 x 105 | NEG | POS |
| GII.15 | 1.7 x 105 | NEG | POS |
| GII.16b | 1.3 x 103 | NEG | POS |
| GII.17b | 1.3 x 103 | NEG | POS |
4 An estimated concentration or titer was provided based on a Ct value (because of the difficulty in culturing norovirus particles, an exact concentration cannot be provided). The Ct value for each clinical specimen in the inclusivity study was extrapolated to the titer obtained from the LoD study for wellcharacterized GI and GII samples using a standard curve at CDC.
b Naked RNA transcripts were used for these strains; clinical samples were not available at the time of testing.
Potentially Interfering Substances
Potentially interfering substances that may be present in the stool were evaluated directly relative to the performance of the Xpert Norovirus Assay. Potentially interfering substances included hemoglobin, mucin, cholesterol, triglycerides and whole blood, plus additional endogenous and exogenous substances listed in Table 5-5.
Negative samples were tested in replicates of 8 with each substance in a negative stool matrix to determine the effect on the performance of the sample processing control (SPC). Positive samples were tested in replicates of 8 per substance with one Norovirus GI and one Norovirus GII clinical isolate near the LoD.
All results were compared to positive and negative controls prepared in negative stool matrix. All valid positive and negative control samples were correctly reported using the Xpert Norovirus Assay.
Inhibition of the Xpert Norovirus Assay was observed in the presence of Benzalkonium chloride (1% w/v, 0.2% w/v, and 0.04% w/v). False-negative test results were reported for the Norovirus GII target at (1% w/v) Benzalkonium chloride. In the presence of Barium sulfate (5% w/w), a statistically significant inhibitory effect was observed on the Norovirus GII Ct in positive samples relative to the control (p-value <0.05). No statistically significant effect was observed on the Norovirus GII Ct relative to the control in the presence of Barium sulfate (1% w/w).
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No other potential interfering substances were found to be inhibitory and no falsenegatives were reported for these substances at the concentrations tested.
| Endogenous substances | ||
|---|---|---|
| Substance | Description /ActiveIngredient | ConcentrationTested |
| Cholesterol | Fecal fat/Cholesterol | 5 % w/v |
| Hemoglobin | Hemoglobin human | 12.5 % w/v |
| Mucin | purified Mucin protein | 5 % w/v |
| Steric acid/ Palmitic acid (1:1) | Fatty acids/Steric acid, Palmitic acid | 5 % w/w |
| Triglyceride | Fecal fat/Triglyceride Mix | 5 % w/v |
| Whole Blood | Human Whole Blood | 10 % v/v |
| Exogenous substances | ||
| Substance | Description /ActiveIngredient | ConcentrationTested |
| Acetaminophen | Acetaminophen | 5 % w/v |
| Amoxicillin | Antibiotic/Amoxicillin | 5 % w/v |
| Ampicillin | Ampicillin Sodium Salt | 152 µmol/L |
| Aspartame | Aspartame | 5 % w/v |
| Barium sulfate | Contrast medium/Bariumsulfate | 5 % w/w, 1% w/w |
| Benzalkoniumchloride Commercialalcohol | Antiseptic Towelettes/Benzalkonium Chloride inethanol | 1 %, 0.2 %, 0.04 %w/v |
| Bismuth subsalicylate | Bismuth (III) Subsalicylate(an active ingredient inPeptobismol) | 1 % w/v |
| CaCO3 | Calcium Carbonate | 5 % w/v |
| Hydrocortisone | Hydrocortisone | 50 % w/v |
| Ibuprofen | Ibuprofen | 5% w/v |
| Imodium | Loperamide HCl | 5 % v/v |
| Kaopectate | Attapulgite | 5 mg/mL |
| Metronidazole | Metronidazole | 5 % w/v |
| Mycostatin | Nystatin | 50 % w/w |
Table 5-5: Potentially Interfering Substances in Xpert Norovirus Assay
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| Exogenous substances | ||
|---|---|---|
| Substance | Description /ActiveIngredient | ConcentrationTested |
| Novaluzid | Mg(OH)2, Al(OH)3 andMgCO3 | 5 % w/v |
| Polymyxin B sulfateBacitrin zinc | Polysporin/Polymyxin BSulfate and Bacitracin Zinc | 50 % w/v |
| Pursennid | Sennaglycosides | 5 % w/v |
| Rexall Mineral oillaxative | Mineral Oil | 50 % w/v |
Carry-Over Contamination
A study was conducted to demonstrate that single-use, self-contained GeneXpert cartridges prevent carry-over contamination in negative samples followed by very high positive samples in the same GeneXpert module. The study consisted of a negative sample processed in the same GeneXpert module immediately followed by a highly positive Norovirus GII sample. This testing scheme was repeated 21 times between two GeneXpert modules for a total of 42 runs for 20 positive and 22 negative specimens. Nineteen (19) positive samples were correctly reported as NORO GI NOT DETECTED: NORO GII DETECTED and one positive sample was reported as an ERROR. All 22 negative samples were correctly reported as NORO GI NOT DETECTED: NORO GII NOT DETECTED.
Linearity
Not applicable, the Xpert Norovirus Assay is a qualitative assay.
Clinical Performance
Clinical Studies: Performance characteristics of the Xpert Norovirus Assay were evaluated at seven institutions in the U.S. and the E.U. The study specimens consisted of raw or unpreserved unformed stool specimens from subjects with symptoms of acute gastroenteritis. The Xpert Norovirus Assay performance was compared to a composite reference test method performed at the CDC (Atlanta, GA).
A total of 1403 specimens were tested for Norovirus GI by the Xpert Norovirus Assay and the composite reference test. Of the 1403 specimens, 914 were fresh, prospectively collected and 489 were frozen, archived specimens. A total of 1401 specimens were tested for Norovirus GII by the Xpert Norovirus Assay and the composite reference test. Of the 1401 specimens, 914 were fresh, prospectively collected and 487 were frozen, archived specimens.
On fresh, prospectively collected specimens, the Xpert Norovirus Assay demonstrated 100% PPA and 99.6% NPA for detection of Norovirus GI . relative to the composite
{17}------------------------------------------------
reference test (Table 5-6). The Xpert Norovirus Assay demonstrated 98.5% PPA and 98.8% NPA for detection of Norovirus GII (Table 5-7).
On frozen, archived specimens, the Xpert Norovirus Assay demonstrated 98.1%, PPA and 94.6%, NPA for detection of Norovirus GI , relative to the composite reference test (Table 5-8). The Xpert Norovirus Assay demonstrated 100% PPA and 96.8% NPA for detection of Norovirus GII (Table 5-9).
| vs. Composite Reference Test – Fresh Specimens | ||||
|---|---|---|---|---|
| Composite Reference Test | ||||
| POS | NEG | Total | ||
| Xpert Norovirus | POS | 12 | 4 | 16 |
| NEG | 0 | 898 | 898 | |
| Total | 12 | 902 | 914 | |
| PPA % (95% CI) | 100% (95% CI: 73.5-100) | |||
| NPA % (95% CI) | 99.6% (95% CI: 98.9-99.9) |
Table 5-6. Xpert Norovirus Assay Performance for GI ys. Composite Reference Test - Fresh Specimens
Table 5-7. Xpert Norovirus Assay Performance for GII vs. Composite Reference Test - Fresh Specimens
| Composite Reference Test | ||||
|---|---|---|---|---|
| POS | NEG | Total | ||
| Xpert Norovirus | POS | 64 | 10 | 74 |
| NEG | 1 | 839 | 840 | |
| Total | 65 | 849 | 914 | |
| PPA % (95% CI)NPA % (95% CI) | 98.5% (95% CI: 91.7-100)98.8% (95% CI: 97.8-99.4) |
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| Composite Reference Test | ||||
|---|---|---|---|---|
| POS | NEG | Total | ||
| Xpert Norovirus | POS | 101 | 21 | 122 |
| NEG | 2 | 365 | 367 | |
| Total | 103 | 386 | 489 | |
| PPA % (95% CI) | 98.1% (95% CI: 93.2-99.8) | |||
| NPA % (95% CI) | 94.6% (95% CI: 91.8-96.6) |
Table 5-8. Xpert Norovirus Assay Performance for GI vs. Composite Reference Test - Frozen Specimens
Table 5-9. Xpert Norovirus Assay Performance for GII vs. Composite Reference Test - Frozen Specimens
| Composite Reference Test | ||||
|---|---|---|---|---|
| POS | NEG | Total | ||
| Xpert Norovirus | POS | 109 | 12 | 121 |
| NEG | 0 | 366 | 366 | |
| Total | 109 | 378 | 487 | |
| PPA % (95% CI) | 100% (95% CI: 96.7-100) | |||
| NPA % (95% CI) | 96.8% (95% CI: 94.5-98.3) |
Reproducibility Study
A panel of 7 specimens with varying concentrations of Norovirus GI and Norovirus GII was tested two times on five different days by two different operators, at each of three sites (7 samples x 2 times/day x 5 days x 2 operators x 3 sites). One lot of Xpert Norovirus Assay cartridges was used at each of the 3 testing sites. The Xpert Norovirus Assay was performed according to the Xpert Norovirus Assay procedure. Results are summarized in Table 5-10.
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| Sample ID | Site 1 | Site2 | Site3 | Overall |
|---|---|---|---|---|
| Neg | 100%(20/20) | 100%(20/20) | 100%(20/20) | 100%(60/60) |
| GI -High Neg | 30.0%(6/20) | 15.0%(3/20) | 30.0%(6/20) | 25.0%(15/60) |
| GI -Low Pos | 100%(20/20) | 85.0%(17/20) | 95.0%(19/20) | 93.3%(56/60) |
| GI -Mod Pos | 100%(19/19) | 100%(20/20) | 100%(20/20) | 100%(59/59)a |
| GII -High Neg | 25.0%(5/20) | 30.0%(6/20) | 35.0%(7/20) | 30.0%(18/60) |
| GII -Low Pos | 100%(20/20) | 95.0%(19/20) | 90.0%(18/20) | 95.0%(57/60) |
| GII -Mod Pos | 95.0%(19/20) | 100%(20/20) | 100%(20/20) | 98.3%(59/60) |
Table 5-10: Summary of Reproducibility Results
ª One sample 2x indeterminate.
reproducibility of the Xpert Norovirus Assay was also evaluated in terms of the fluorescence signal expressed in Ct values for each target detected. The mean, standard deviation (SD), and coefficient of variation (CV) between-sites, between-days, and between-operators for each panel member are presented in Table 5-11.
| Sample | AssayChannel(Analyte) | Na | MeanCt | Between-Site | Between-Day | Between-Operator | Within-Assay | Total | |||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| SD | CV(%) | SD | CV(%) | SD | CV(%) | SD | CV(%) | SD | CV(%) | ||||
| Neg | SPC | 60 | 31.9 | 0.17 | 0.5 | 0.06 | 0.2 | 0.06 | 0.2 | 0.26 | 0.8 | 0.32 | 1.0 |
| GI - High Neg | GI | 60 | 39.4 | 0 | 0 | 0.46 | 1.2 | 0 | 0 | 1.80 | 4.6 | 1.86 | 4.7 |
| GI - Low Pos | GI | 59 | 37.9 | 0.29 | 0.8 | 0 | 0 | 0.36 | 1.0 | 1.03 | 2.7 | 1.13 | 3.0 |
| GI - Mod Posb | GI | 57 | 34.7 | 0.09 | 0.2 | 0.07 | 0.2 | 0 | 0 | 0.41 | 1.2 | 1.01 | 1.2 |
| GII - High Neg | GII | 54 | 38.9 | 0 | 0 | 0 | 0 | 0.77 | 2.0 | 1.77 | 4.5 | 1.93 | 5.0 |
| GII - Low Pos | GII | 60 | 37.3 | 0 | 0 | 0 | 0 | 0.58 | 1.6 | 1.33 | 3.6 | 1.45 | 3.9 |
| GII - Mod Posb | GII | 59 | 34.3 | 0.22 | 0.6 | 0 | 0 | 0 | 0 | 0.45 | 1.3 | 0.50 | 1.5 |
ª Results with non-zero Ct values out of 60.
b =3 sample outliers (2 GI Mod Pos and 1 GII Mod Pos) that were more than 5 standard deviations from the mean were considered outliers and were removed from the analysis.
Instrument System Precision
An in-house precision study was conducted to compare the performance of the GeneXpert Dx and the GeneXpert Infinity instrument systems. A panel of 7 samples with varying concentrations of Norovirus GI and Norovirus GII was tested on 12 different
{20}------------------------------------------------
days by two operators. Each operator conducted four runs of each panel of samples per day on each of the two instrument systems (7 samples x 4 times/day x 12 days x 2 operators x 2 instrument systems). Three lots of Xpert Norovirus Assay cartridges were used for the study. The Xpert Norovirus Assay was performed according to the Xpert Norovirus Assay procedure. Results are summarized in Table 5-12.
| Sample | GeneXpert Dx | Infinity | % TotalAgreementby Sample | ||||
|---|---|---|---|---|---|---|---|
| Op 1 | Op 2 | Inst | Op 1 | Op 2 | Inst | ||
| Neg | 100%(48/48) | 100%(48/48) | 100%(96/96) | 100%(48/48) | 100%(48/48) | 100%(96/96) | 100%(192/192) |
| GI - High Neg | 14.6%(7/48) | 10.4%(5/48) | 12.5%(12/96) | 14.6%(7/48) | 25.0%(12/48) | 19.8%(19/96) | 16.2%(31/192) |
| GI - Low Pos | 100%(48/48) | 97.9%(47/48) | 99.0%(95/96) | 97.9%(47/48) | 97.9%(47/48) | 97.9%(94/96) | 98.4%(189/192) |
| GI - Mod Pos | 100%a(47/47) | 100%(48/48) | 100%(95/95) | 100%(48/48) | 100%(48/48) | 100%(96/96) | 100%(191/191) |
| GII - High Neg | 25.0%(12/48) | 29.2%(14/48) | 27.1%(26/96) | 29.2%(14/48) | 31.3%(15/48) | 30.2%(29/96) | 28.7%(55/192) |
| GII - Low Pos | 89.6%(43/48) | 89.6%(43/48) | 89.6%(86/96) | 83.3%(40/48) | 95.7%(44/46) | 87.5%(84/96) | 88.5%(170/192) |
| GII - Mod Pos | 100%(48/48) | 100%(48/48) | 100%(96/96) | 100%(48/48) | 100%b(47/47) | 100%(95/95) | 100%(191/191) |
Table 5-12. Summary of Instrument System Precision Results (Dx vs. Infinity)
The precision of the Xpert Norovirus Assay was also evaluated in terms of the fluorescence signal expressed in Ct values for each target detected. The mean, standard deviation (SD), and coefficient of variation (CV) between-instruments, between-lots, between-days, between-operators, and within-assays for each panel member are presented in Table 5-13.
{21}------------------------------------------------
| Sample | AssayChannel(Analyte) | Na | MeanCt | Between-Instrument | Between-Lot | Between-Day | Between-Operator | Within-Assay | Total | ||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| SD | CV(%) | SD | CV(%) | SD | CV(%) | SD | CV(%) | SD | CV(%) | SD | CV(%) | ||||
| Neg | SPC | 192 | 31.8 | 0 | 0 | 0.44 | 1.4 | 0 | 0 | 0.08 | 0.2 | 0.39 | 1.2 | 0.59 | 1.9 |
| GI -High Neg | GI | 188 | 38.6 | 0.19 | 0.5 | 0.25 | 0.7 | 0.18 | 0.5 | 0 | 0 | 1.40 | 3.6 | 1.45 | 3.8 |
| GI -Low Pos | GI | 192 | 37.1 | 0.39 | 1.1 | 0.26 | 0.7 | 0.19 | 0.5 | 0 | 0 | 0.95 | 2.6 | 1.08 | 2.9 |
| GI -Mod Pos | GI | 191 | 34.0 | 0 | 0 | 0.36 | 1.1 | 0.04 | 0.1 | 0.08 | 0.2 | 0.38 | 1.1 | 0.53 | 1.6 |
| GII -High Neg | GII | 178 | 38.7 | 0.16 | 0.4 | 0 | 0 | 0.29 | 0.7 | 0 | 0 | 2.03 | 5.3 | 2.06 | 5.3 |
| GII -Low Pos | GII | 187 | 37.6 | 0.10 | 0.2 | 0 | 0 | 0 | 0 | 0.45 | 1.2 | 1.65 | 4.4 | 1.71 | 4.6 |
| GII -Mod Pos | GII | 191 | 34.3 | 0 | 0 | 0.09 | 0.2 | 0 | 0 | 0.17 | 0.5 | 0.42 | 1.2 | 0.46 | 1.3 |
Table 5-13: Summary of Precision Data
ª Results with non-zero Ct values out of 192.
Conclusions
The results of the nonclinical analytical and clinical performance studies summarized above demonstrate that the Xpert Norovirus Assay is safe and effective for its intended use and is substantially equivalent to the predicate device.
§ 866.3990 Gastrointestinal microorganism multiplex nucleic acid-based assay.
(a)
Identification. A gastrointestinal microorganism multiplex nucleic acid-based assay is a qualitativein vitro diagnostic device intended to simultaneously detect and identify multiple gastrointestinal microbial nucleic acids extracted from human stool specimens. The device detects specific nucleic acid sequences for organism identification as well as for determining the presence of toxin genes. The detection and identification of a specific gastrointestinal microbial nucleic acid from individuals exhibiting signs and symptoms of gastrointestinal infection aids in the diagnosis of gastrointestinal infection when used in conjunction with clinical evaluation and other laboratory findings. A gastrointestinal microorganism multiplex nucleic acid-based assay also aids in the detection and identification of acute gastroenteritis in the context of outbreaks.(b)
Classification. Class II (special controls). The special controls are set forth in FDA's guideline document entitled: “Class II Special Controls Guideline: Gastrointestinal Microorganism Multiplex Nucleic Acid-Based Assays for Detection and Identification of Microorganisms and Toxin Genes from Human Stool Specimens.” For availability of the guideline document, see § 866.1(e).