The Xpert® MRSA/SA Skin and Soft Tissue Infection test (Xpert MRSA/SA SSTI test) performed on the GeneXpert® Instrument Systems is a qualitative in vitro diagnostic test intended for the detection of Staphylococcus aureus (SA) and methicillin-resistant Staphylococcus aureus (MRSA) from skin and soft tissue infection swabs. The test utilizes automated real-time polymerase chain reaction (PCR) to detect MRSA/SA DNA. The Xpert MRSA/SA SSTI test is indicated for use in conjunction with other laboratory tests, such as microbiology culture, and clinical data available to the clinician as an aid in the detection of MRSA/SA from skin and soft tissue infections. The Xpert MRSA/SA SSTI test is not intended to monitor treatment for MRSA/SA infections. Concomitant cultures for SA and MRSA are necessary to recover organisms for susceptibility testing or epidemiological typing. In a mixed culture containing MRSA/SA and other organisms (e.g., Gram-negative bacilli, yeast), results can be false negative or variable depending on the concentration of MRSA/SA present, particularly if the concentration of MRSA/SA is close to the limit of detection (LoD) of the test.

Device Description

The Xpert MRSA/SA SSTI (Xpert MRSA/SA Skin and Soft Tissue Infection) test is an automated in vitro diagnostic DNA test for the qualitative, simultaneous detection of Staphylococcus aureus (SA) and methicillin-resistant Staphylococcus aureus (MRSA) directly from skin and soft tissue specimen swabs. The specimen is collected on a double swab, one of which is placed in a tube containing elution reagent. Following brief vortexing, the eluted material is transferred to a different, uniquely labeled sample chamber of a disposable fluidic cartridge (the Xpert MRSA/SA SSTI cartridge).

The test is performed on the GeneXpert® Instrument Systems (comprised of the GeneXpert® Dx System, GeneXpert® System with Touchscreen, and GeneXpert® Infinity System). In the GeneXpert® Instrument Systems, sample preparation, amplification, and real-time detection are all fully automated and completely integrated. The platform requires the use of singleuse disposable cartridges that hold the PCR reagents and host the PCR process. Because the cartridges are self-contained, cross-contamination between samples is minimized.

The user initiates a test from the system user interface of the GeneXpert® Instrument Systems platform and places the cartridge with sample into a GeneXpert® instrument system which performs hands-off real-time, multiplex polymerase chain reaction (PCR) for detection of SA and MRSA DNA.

Depending upon the specific instrument, a GeneXpert® instrument system may contain 1–80 modules, each which are randomly accessible and 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 ICORE® thermocycler for performing real-time PCR and detection.

The Xpert MRSA/SA SSTI test kit includes reagents for the simultaneous detection of the target organisms, SA and MRSA. The primers and probes in the Xpert MRSA/SA SSTI test detect nucleic acid sequences of the staphylococcal protein A (spa), the gene for methicillin/oxacillin resistance (mecA), and staphylococcal cassette chromosome (SCCmec) inserted in the SA chromosomal attB site.

The test includes a sample processing control (SPC) to control for adequate processing of the target bacteria and to monitor the presence of inhibitor(s) in the PCR assay. The SPC also ensures that the PCR conditions (temperature and time) are appropriate for the amplification reaction and that the PCR reagents are functional. The Probe Check Control (PCC) verifies reagent rehydration, PCR tube filling in the cartridge, probe integrity, and dye stability.

The Xpert MRSA/SA SSTI test performed on the GeneXpert® Instrument Systems provides results in approximately 62 minutes.

AI/ML Overview

The provided text is a 510(k) summary for a medical device called Xpert MRSA/SA SSTI. It describes a diagnostic test for Staphylococcus aureus (SA) and methicillin-resistant Staphylococcus aureus (MRSA) from skin and soft tissue infection swabs, performed on the GeneXpert Instrument Systems.

The document does not contain information about the design of a study to prove acceptance criteria using a test set of data with expert ground truth, human reader performance, or multi-reader multi-case studies.

Instead, it details a Special 510(k) submission to modify an already cleared and legally marketed device (Xpert MRSA/SA SSTI, K080837). The specific modification is to include the GeneXpert® Infinity System instruments as a compatible platform for the test.

Therefore, the performance data presented is focused on demonstrating that the performance of the test on the new instrument platform (GeneXpert Infinity) is equivalent to its performance on previously cleared platforms (GeneXpert Dx System, GeneXpert System with Touchscreen). This is a bridging study rather than a primary clinical validation or an AI performance study as implied by many of the questions.

Given this, I cannot answer all your questions as the relevant information is not in the provided text. However, I will answer what is available and clarify what is missing.

Acceptance Criteria and Reported Device Performance

The acceptance criteria here refer to demonstrating equivalent performance of the Xpert MRSA/SA SSTI test when run on the new GeneXpert Infinity System compared to the previously cleared GeneXpert Dx System.

Acceptance Criteria (Implied)	Reported Device Performance
Functional Equivalence: The test should perform equivalently on the new GeneXpert Infinity System as on the predicate GeneXpert Dx System, maintaining the ability to detect MRSA/SA.	Functional Testing: Conducted using both contrived positive (MRSA cells added to negative matrix) and negative (negative matrix only) samples. Each target of the Xpert MRSA/SA SSTI test was analyzed, resulting in a reportable outcome. Study Results: Showed 100% agreement of reportable results, with no statistically significant differences in Ct values observed between assay runs in instruments of the GeneXpert® Dx System and GeneXpert® Infinity System. This demonstrated equivalent performance.
Operational Stability/Hold Time: The maximum acceptable hold time for a prepared cartridge should be verified on the new system.	Prepared Cartridge Hold Time Study: The maximum acceptable hold time for a prepared cartridge was verified as 4 hours.
No impact on performance claims: The modifications should not negatively impact the existing performance claims of the Xpert MRSA/SA SSTI test.	Overall Assessment: The assessment of the results from these studies determined that the performance claims of the Xpert MRSA/SA SSTI test were not impacted by the modifications made to the predicate device.

Study Details (Based on available information)

Sample size used for the test set and the data provenance:
- The document mentions "contrived positive (MRSA cells added to negative matrix) and negative (negative matrix only) samples" for functional testing. It does not provide the specific number of samples (sample size) used in these studies.
- Data Provenance: The data appears to be prospective as it's generated from specific verification studies ("prepared cartridge hold time study and functional testing") conducted for this 510(k) submission. The country of origin is not specified but implicitly North American given the FDA submission.
Number of experts used to establish the ground truth for the test set and the qualifications of those experts:
- This is a molecular diagnostic test, not an AI image analysis device. The "ground truth" for the functional testing would be the known concentration/presence of MRSA/SA cells in the contrived samples. This is established by the assay design and sample preparation, not by expert interpretation.
- Therefore, this question does not apply to the type of study described.
Adjudication method (e.g. 2+1, 3+1, none) for the test set:
- Not applicable. This relates to expert consensus in interpreting complex data, which is not the ground truth methodology for this type of molecular test. The measurements (Ct values, presence/absence of signal) are quantitative and objective.
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, an MRMC study was not done. This is a diagnostic device for detecting specific DNA sequences, not an AI-powered device assisting human readers.
If a standalone (i.e. algorithm only without human-in-the-loop performance) was done:
- The device itself (Xpert MRSA/SA SSTI test on the GeneXpert Instrument Systems) is a standalone automated diagnostic test. Its "performance" is the detection of specific DNA sequences. The studies assess the instrument's ability to run the test and yield equivalent results. The "functional testing" mentioned is effectively the standalone performance of the assay on the new instrument.
The type of ground truth used (expert consensus, pathology, outcomes data, etc.):
- The ground truth for the functional testing was contrived samples with known positive and negative status (e.g., negative matrix, or MRSA cells added to negative matrix where the concentration of MRSA/SA is known). This allows for direct assessment of sensitivity and specificity against a known standard.
The sample size for the training set:
- This device is based on real-time PCR technology, not machine learning that requires a "training set" in the conventional sense. The test's probes and primers are designed based on biological knowledge of the target sequences.
- Therefore, this question does not apply.
How the ground truth for the training set was established:
- Not applicable, as there is no traditional "training set" for this type of diagnostic device.

Summary

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December 18, 2024

Image /page/0/Picture/1 description: The image contains the logos of the Department of Health and Human Services and the Food and Drug Administration (FDA). The Department of Health and Human Services logo is on the left, and the FDA logo is on the right. The FDA logo includes the letters "FDA" in a blue square, followed by the words "U.S. FOOD & DRUG ADMINISTRATION" in blue text.

Cepheid Vidhi Shah Regulatory Affairs Senior Specialist 904 Caribbean Drive Sunnyvale, California 94089

Re: K243625

Trade/Device Name:	Xpert MRSA/SA SSTI
Regulation Number:	21 CFR §866.1640
Regulation Name:	Antimicrobial Susceptibility Test Powder
Regulatory Class:	Class II
Product Code:	NQX, OOI
Dated:	November 22, 2024
Received:	November 25, 2024

Dear Vidhi Shah:

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 (the 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. Although this letter refers to your product as a device, please be aware that some cleared products may instead be combination products. The 510(k) Premarket Notification Database available at https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfpmn/pmn.cfm identifies combination product submissions. 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 (CFR), Title 21, Parts 800 to 898. In addition, FDA may publish further announcements concerning your device in the Federal Register.

Additional information about changes that may require a new premarket notification are provided in the FDA guidance documents entitled "Deciding When to Submit a 510(k) for a Change to an Existing Device" (https://www.fda.gov/media/99812/download) and "Deciding When to Submit a 510(k) for a Software Change to an Existing Device" (https://www.fda.gov/media/99785/download).

Your device is also subject to, among other requirements, the Quality System (QS) regulation (21 CFR $820), which includes, but is not limited to, 21 CFR $820.30, Design controls; 21 CFR §820.90, Nonconforming product; and 21 CFR $820.100, Corrective and preventive action. Please note that regardless of whether a change requires premarket review, the QS regulation requires device manufacturers to review and approve changes to device design and production (21 CFR §820.70 and 21 CFR §820.70) and document changes and approvals in the device master record (21 CFR §820.181).

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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 §801); labeling (21 CFR §801 and §809); medical device reporting (reporting of medical device-related adverse events) (21 CFR §803) for devices or postmarketing safety reporting (21 CFR Part 4, Subpart B) for combination products (see https://www.fda.gov/combination-products/guidance-regulatory-information/postmarketing-safety-reportingcombination-products); good manufacturing practice requirements as set forth in the quality systems (QS) regulation (21 CFR §820) for devices or current good manufacturing practices (21 CFR Part 4) for combination products; and, if applicable, the electronic product radiation control provisions (Sections 531-542 of the Act); 21 CFR Parts 1000-1050.

All medical devices, including Class I and unclassified devices and combination product device constituent parts, are required to be in compliance with the final Unique Device Identification System rule ("UDI Rule"). The UDI Rule requires, among other things, that a device bear a unique device identifier (UDI) on its label and package (21 CFR §801.20(a)) unless an exception or alternative applies (21 CFR §801.20(b)) and that the dates on the device label be formatted in accordance with 21 CFR $801.18. The UDI Rule (21 CFR §830.300(a) and §830.320(b)) also requires that certain information be submitted to the Global Unique Device Identification Database (GUDID) (21 CFR 8830 Subpart E). For additional information on these requirements, please see the UDI System webpage at https://www.fda.gov/medical-device-advicecomprehensive-regulatory-assistance/unique-device-identification-system-udi-system.

Also, please note the regulation entitled, "Misbranding by reference to premarket notification" (21 CFR $807.97). For questions regarding the reporting of adverse events under the MDR regulation (21 CFR $803), please go to https://www.fda.gov/medical-devices/medical-device-safety/medical-device-reporting-mdrhow-report-medical-device-problems.

For comprehensive regulatory information about medical devices and radiation-emitting products, including information about labeling regulations, please see Device Advice (https://www.fda.gov/medicaldevices/device-advice-comprehensive-regulatory-assistance) and CDRH Learn (https://www.fda.gov/training-and-continuing-education/cdrh-learn). Additionally, you may contact the Division of Industry and Consumer Education (DICE) to ask a question about a specific regulatory topic. See the DICE website (https://www.fda.gov/medical-device-advice-comprehensive-regulatoryassistance/contact-us-division-industry-and-consumer-education-dice) for more information or contact DICE by email (DICE@fda.hhs.gov) or phone (1-800-638-2041 or 301-796-7100).

Sincerely,

Ribhi Shawar -S

Ribhi Shawar, Ph.D. (ABMM) Branch Chief General Bacteriology and Antimicrobial Susceptibility Branch Division of Microbiology Devices OHT7: Office of In Vitro Diagnostics OPEQ: Office of Product Evaluation and Quality Center for Devices and Radiological Health

Enclosure:

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Indications for Use

510(k) Number (if known) K243625

Device Name Xpert® MRSA/SA SSTI

Indications for Use (Describe)

The Xpert® MRSA/SA Skin and Soft Tissue Infection test (Xpert MRSA/SA SSTI test) performed on the GeneXpert® Instrument Systems is a qualitative in vitro diagnostic test intended for the detection of Staphylococcus aureus (SA) and methicillin-resistant Staphylococcus aureus (MRSA) from skin and soft tissue infection swabs. The test utilizes automated real-time polymerase chain reaction (PCR) to detect MRSA/SA SSTI test is indicated for use in conjunction with other laboratory tests, such as microbiology culture, and clinical data available to the clinician as an aid in the detection of MRSA/SA from skin and soft tissue infections. The Xpert MRSA/SA SSTI test is not intended to monitor treatment for MRSA/SA infections. Concomitant cultures for SA and MRSA are necessary to recover organisms for susceptibility testing or epidemiological typing. In a mixed culture containing MRSA/SA and other organisms (e.g., Gram-negative bacilli, yeast), results can be false negative or variable depending on the concentration of MRSA/SA present, particularly if the concentration of MRSA/SA is close to the limit of detection (LoD) of the test.

Type of Use (Select one or both, as applicable)

X Prescription Use (Part 21 CFR 801 Subpart D)

| | Over-The-Counter Use (21 CFR 801 Subpart C)

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510(k) Summary for Xpert MRSA/SA SSTI

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Image /page/4/Picture/0 description: The image shows the logo for Cepheid, a molecular diagnostics company. The logo features a stylized blue swoosh above the company name, "Cepheid.". Below the company name is the text "Xpert® MRSA/SA SSTI", which likely refers to one of Cepheid's diagnostic tests for detecting methicillin-resistant Staphylococcus aureus (MRSA) and Staphylococcus aureus (SA) in skin and soft tissue infections (SSTI).

1	510(K) SUMMARY
	1.1 DEVICE DESCRIPTION
	1.2 DEVICE INTENDED USE
	1.3 TECHNICAL CHARACTERISTICS
	1.4 SUBSTANTIAL EQUIVALENCE………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………
	1.5 SUMMARY OF PERFORMANCE DATA
	1.6 CONCLUSION

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Image /page/5/Picture/0 description: The image shows the Cepheid logo and the text "Xpert® MRSA/SA SSTI". The Cepheid logo is a stylized blue shape above the word "Cepheid.". The text "Xpert® MRSA/SA SSTI" is below the logo in a smaller font.

1 510(k) Summary

As required by 21 CFR §807.92.

Submitted by:	Cepheid904 Caribbean DriveSunnyvale, CA 90489Phone Number: (408) 541-4191
Contact:	Vidhi Shah, Senior Regulatory Affairs Specialist
Date of Preparation:	November 22, 2024
Device:
Trade name	Xpert® MRSA/SA SSTI
Common name	Xpert MRSA/SA SSTI
Type of Test	Nucleic Acid Amplification Test, DNA, Staphylococcus aureus(SA) and Methicillin-resistant Staphylococcus aureus (MRSA),qualitative
Regulation number:	21 CFR §866.1640
Classification name:	Antimicrobial susceptibility test powder
Product code:	NQX, OOI
ClassificationAdvisory Panel	Microbiology (83)
Prescription Use	Yes
Predicate DeviceAssay:	Xpert MRSA/SA SSTI (K080837)

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Image /page/6/Picture/1 description: The image shows the Cepheid logo, which includes a blue graphic element above the word "Cepheid." Below the logo is the text "Xpert® MRSA/SA SSTI". The text appears to be the name of a product or service offered by Cepheid.

1.1 Device Description

The Xpert MRSA/SA SSTI test performed on the GeneXpert® Instrument Systems provides results in approximately 62 minutes.

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Image /page/7/Picture/1 description: The image shows the logo for Cepheid, a molecular diagnostics company. Below the logo is the text "Xpert® MRSA/SA SSTI". The text likely refers to a diagnostic test for methicillin-resistant Staphylococcus aureus (MRSA) and Staphylococcus aureus (SA) skin and soft tissue infections (SSTI).

Each instrument in the GeneXpert® instrument family is equipped with Windows OS-based personal computer preloaded with software applications for running tests and viewing the results, as described in Table 1.

Table 1: Instrument Systems and Software in the GeneXpert® Instrument Family
Members

Instrument Family	Instrument FamilyMembers	Systems Softwarespecific to InstrumentFamily Member	GeneXpert® Instruments
GeneXpert®Instrument Systems	GeneXpert® DxSystem	GeneXpert Dx	GX-I† GX-II GX-IV GX-XVI
	GeneXpert® Systemwith Touchscreen	Cepheid OS	GX-II GX-IV GX-XVI
	GeneXpert®Infinity System	GeneXpert Xpertise	GeneXpert Infinity-48s GeneXpert Infinity-80

T No longer manufactured or distributed in the United States but is in circulation in the market

1.2 Device Intended Use

The Xpert® MRSA/SA Skin and Soft Tissue Infection test (Xpert MRSA/SA SSTI test) performed on the GeneXpert® Instrument Systems is a qualitative in vitro diagnostic test intended for the detection of Staphylococcus aureus (SA) and methicillin-resistant Staphylococcus aureus (MRSA) from skin and soft tissue infection swabs. The test utilizes automated real-time polymerase chain reaction (PCR) to detect MRSA/SA DNA. The Xpert MRSA/SA SSTI test is indicated for use in conjunction with other laboratory tests, such as microbiology culture, and clinical data available to the clinician as an aid in the detection of MRSA/SA from skin and soft tissue infections. The Xpert MRSA/SA SSTI test is not intended to monitor treatment for MRSA/SA infections. Concomitant cultures for SA and MRSA are necessary to recover organisms for susceptibility testing or epidemiological typing. In a mixed culture containing MRSA/SA and other organisms (e.g., Gram-negative bacilli, yeast), results can be false negative or variable depending on the concentration of MRSA/SA present. particularly if the concentration of MRSA/SA is close to the limit of detection (LoD) of the test.

1.3 Technical Characteristics

The Xpert MRSA/SA SSTI test has the same technological characteristics as the predicate device.

1.4 Substantial Equivalence

The purpose of this Special 510(k) submission is to modify the cleared, legally marketed device (Xpert MRSA/SA SSTI) to include the GeneXpert® Infinity System instruments (see Table 1 above). The Xpert MRSA/SA SSTI test was originally cleared for use on the GeneXpert® Dx System (K080837). Both the GeneXpert Dx System and the GeneXpert Infinity System are

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Image /page/8/Picture/0 description: The image shows the Cepheid logo with the text "Xpert® MRSA/SA SSTI" underneath it. The Cepheid logo consists of a stylized blue wing-like shape above the word "Cepheid." The text "Xpert® MRSA/SA SSTI" is written in a smaller font size than the word "Cepheid."

members of the instrument family "GeneXpert® Instrument Systems" which is now incorporated in the Intended Use/Indications for Use of this device. Table 2 shows the similarities and Table 3 shows the differences between the Xpert MRSA/SA SSTI test and predicate device. The differences between Xpert MRSA/SA SSTI test and predicate device do not raise different questions of safety and effectiveness.

		Table 2. Similarities between Xpert MRSA/SA SSTI and the Predicate Device

		Similarities
Attribute	Modified DeviceXpert® MRSA/SA SSTI	Predicate (K080837) DeviceXpert® MRSA/SA SSTI
Regulation	Same	21 CFR §866.1640
Product Code	Same	Antimicrobial susceptibility test powderNQXSystem, Nucleic Acid Amplification Test, DNA, MethicillinResistant Staphylococcus Aureus, Direct Specimen
Device Class	Same	ΟΟΙReal Time Nucleic Acid Amplification SystemClass II
Purpose of Use	Same	Identification of Staphylococcus aureus (SA) andMethicillin-resistant Staphylococcus aureus (MRSA)
Specimen	Same	Skin and soft tissue infection swabs
Test Technology	Same	Nucleic Acid (DNA) Amplification (real time PCR) forqualitative detection of SA and MRSA with specific primersand TaqMan probesDetection: Fluorogenic target-specific hybridization
Test Automation	Same	Fully automated DNA extraction, detection, and resultsinterpretation
Test Format	Same	Single use in disposable, multi-chambered, fluidic cartridge
Test Targets(Sequence)	Same	Staphylococcal protein A (spa gene), sequence specificto S. aureus species Sequence specific to Methicillin/oxacillin resistance(mecA gene) Sequence incorporating the insertion site (attBssc) ofStaphylococcal Cassette Chromosome mec (SCCmec)for detection of MRSA
Internal Controls	Same	Sample Processing Control (SPC) Probe Check Control (PCC)
Intended Useenvironment	Same	Professional Use, by trained users
Test Access	Same	Prescription Use only

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Image /page/9/Picture/1 description: The image contains the logo for Cepheid, a molecular diagnostics company. The logo features a stylized blue graphic element above the company name, "Cepheid." Below the company name is the text "Xpert® MRSA/SA SSTI", which likely refers to a specific diagnostic test offered by Cepheid for detecting MRSA and Staphylococcus aureus in skin and soft tissue infections.

Table 3. Differences between Xpert MRSA/SA SSTI and the Predicate Device
--------------------------------------------------------------------------

Differences
Attribute	Modified Device	Predicate(K080837)
	Xpert® MRSA/SA SSTI	Xpert® MRSA/SA SSTI
Time to Results	Approximately 62 minutes	Approximately 50 minutes
IntendedUse/Indicationsfor Use	The Xpert® MRSA/SA Skin and Soft TissueInfection test (Xpert® MRSA/SA SSTI test)performed on the GeneXpert® InstrumentSystems is a qualitative in vitro diagnostictest intended for the detection ofStaphylococcus aureus (SA) andmethicillin-resistant Staphylococcus aureus(MRSA) from skin and soft tissue infectionswabs. The test utilizes automated real-timepolymerase chain reaction (PCR) to detectMRSA/SA DNA. The Xpert MRSA/SASSTI test is indicated for use in conjunctionwith other laboratory tests, such asmicrobiology culture, and clinical dataavailable to the clinician as an aid in thedetection of MRSA/SA from skin and softtissue infections. The Xpert MRSA/SASSTI test is not intended to monitortreatment for MRSA/SA infections.Concomitant cultures for SA and MRSA arenecessary to recover organisms forsusceptibility testing or epidemiologicaltyping. In a mixed culture containingMRSA/SA and other organisms (e.g.,Gram-negative bacilli, yeast), results can befalse negative or variable depending on theconcentration of MRSA/SA present,particularly if the concentration ofMRSA/SA is close to the limit of detection(LoD) of the test.	The Cepheid Xpert MRSA/SA Skin andSoft Tissues Infection Assay (Xpert®MRSA/SA SSTI Assay) performed in theGeneXpert® Dx System is a qualitative invitro diagnostic test intended for thedetection of Staphylococcus aureus (SA)and methicillin-resistant Staphylococcusaureus (MRSA) from skin and soft tissueinfection swabs. The test utilizes automatedreal-time polymerase chain reaction (PCR)to detect MRSA/SA DNA. The XpertMRSA/SA SSTI Assay is indicated for usein conjunction with other laboratory testssuch as microbiology culture, and clinicaldata available to the clinician as an aid in thedetection of MRSA/SA from skin andsoft tissue infections. The Xpert MRSA/SASSTI Assay is not intended to monitortreatment for MRSA/SA infections.Concomitant cultures for SA and MRSAare necessary to recover organisms forsusceptibility testing or epidemiologicaltyping.In a mixed culture containing MRSA/SAand other organisms (e.g. Gram negativebacilli, yeast), results can be false negativeor variable depending on the concentrationof MRSA/SA present, particularly if theconcentration of MRSA/SA is close to theLoD of the assay.
InstrumentSystems	GeneXpert Dx SystemGeneXpert System with TouchscreenGeneXpert Infinity System	GeneXpert Dx SystemGeneXpert System with Touchscreen
Systems Softwarefor InstrumentFamily	GeneXpert Dx softwareCepheid OS softwareXpertise software	GeneXpert Dx softwareCepheid OS software

1.5 Summary of Performance Data

The performance of the Xpert MRSA/SA SSTI test when used with the GeneXpert® Infinity System instruments was assessed through verification studies, including a prepared cartridge hold time study and functional testing.

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Image /page/10/Picture/1 description: The image shows the Cepheid logo, which includes a stylized blue wing-like design above the word "Cepheid." Below the logo, the text "Xpert® MRSA/SA SSTI" is displayed. The text likely refers to a diagnostic test or product related to MRSA/SA SSTI, which are types of bacterial infections.

Hold time refers to the duration between the preparation of the cartridge (i.e., addition of sample) and the initiation of the test. The maximum acceptable hold time for a prepared cartridge was verified as 4 hours.

Functional testing was conducted using both contrived positive (MRSA cells added to negative matrix) and negative (negative matrix only) samples. Each target of the Xpert MRSA/SA SSTI test was analyzed, resulting in a reportable outcome. The study results showed 100% agreement of reportable results, with no statistically significant differences in Ct values observed between assay runs in instruments of the GeneXpert® Dx System and GeneXpert® Infinity System. This study demonstrated equivalent performance of the Xpert MRSA/SA SSTI test when performed on any member of the GeneXpert® Instrument Systems family.

The assessment of the results from these studies determined that the performance claims of the Xpert MRSA/SA SSTI test were not impacted by the modifications made to the predicate device.

1.6 Conclusion

The results of the verification studies demonstrated that the performance of the modified Xpert MRSA/SA SSTI test on the GeneXpert Infinity System is equivalent to the performance of the predicate device, the original Xpert MRSA/SA SSTI (K080837), and that the modifications proposed in the modified device have not changed the fundamental scientific technology of the predicate device.

Regulation Number and Section

§ 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).