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FDA Offers Guidance for MRSA Tests

By a GenomeWeb staff reporter

NEW YORK (GenomeWeb News) – The US Food and Drug Administration has issued a new draft guidance and recommendations for how nucleic acid-based in vitro diagnostic tests for Staphylococcus aureus (SA) should perform and be tested for their analytical and clinical validity.

The document is aimed at providing companies and agency staff with guidance for tests for detecting and differentiating methicillin-resistant Staphylococcus aureus (MRSA) and SA, which are used to prevent and manage infections primarily in health care settings.

The guidance specifically provides FDA recommendations on studies used for Class II premarket submission, and it includes examples of strains recommended for analytical sensitivity and inclusivity studies, as well as microorganism types that are recommended for analytical specificity studies.

FDA stressed in the document that at the current time the guidance does not mean firms must follow its recommendations, rather it reflects "the agency's current thinking" and "should be viewed only as recommendations" that are suggested, but not required.

The current standard test for detecting MRSA uses traditional cultures, but swifter nucleic acid-based IVD tests for MRSA and SA "represent an important tool for infection control programs to aid in the prevention and control of MRSA infection in healthcare settings," according to the FDA document.

These genomic tests also are useful for aiding in patient management, in making diagnoses from skin and soft tissue infections, and detecting MRSA/SA from certain blood culture bottles, the guidance states.

However, FDA has identified some potential issues with the safety or effectiveness of nucleic acid-based assays. The test could fail to function, which could result in inaccurate results or the incorrect interpretation of results. Failures could lead to false positive MRSA results, for example, which could cause patients to be treated unnecessarily, or to a false negative, which could leave MRSA patients going untreated.

These failures also could lead to inappropriate infection control responses and could potentially delay preventative and safety measures.

"Therefore, establishing the performance of these devices and understanding the risks that might be associated with the use of these devices is critical to their safe and effective use," FDA said in the document.

The guidance includes recommendations covering the development of targets for the tests' intended uses, for their testing methodologies and platforms, specimen types, hardware and software requirements, necessary reagents, and other traits of the tests.

The guidelines also provide recommendations covering risk assessment techniques and methods, the use of positive, negative, and other controls, and methods for interpreting and reporting test results.

FDA also offers guidance on studies that test developers should use to determine analytical sensitivity, reactivity, and specificity, and provides recommendations about substances that could interfere with the tests.

Among the companies currently offering nucleic acid-based tests for MRSA and SA are Cepheid, Becton Dickinson, and Roche.

In July 2010, Cepheid voluntarily engaged in a recall of its Xpert MRSA/SA blood culture product, which runs on its GeneXpert PCR platform, due to false negative reports of MRSA.

The company said at the time that it would change the labeling on its test because a novel MRSA strain was causing false negative reports, and that it had notified FDA of one adverse event.

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