This article, originally published July 1, has been updated from a previous version to include comments from an FDA spokesperson.
Cepheid said today that it is voluntarily recalling all lots of its Xpert MRSA/SA blood culture product, which runs on its GeneXpert PCR platform, due to false negative reports of methicillin-resistant Staphylococcus aureus.
The company said that customers can continue using the product but will need to perform confirmatory testing for any MRSA-negative/SA-positive results.
"The Xpert MRSA/SA BC product produces false-negative MRSA results, which could potentially contribute to incorrect treatment of an MRSA infection," the company said. "Although the product appears to continue to meet performance claims as outlined in the current product labeling, an ongoing failure investigation has identified the emergence of novel MRSA strain types as one of the causes of false-negative MRSA results."
The company added that the failure investigation "has not fully determined the remaining causes of the false-negative MRSA results."
Cepheid said it issued the recall after learning of "rare, false-negative MRSA results from the testing of blood culture samples," and that it has notified the US Food and Drug Administration of "one adverse event."
As a result of the false negative results, if the test returns a MRSA-negative/SA-positive result, it should be interpreted as "MRSA indeterminate/SA positive, antimicrobial susceptibility testing pending," Cepheid said. Further testing should be performed using an "FDA-cleared, phenotypic antimicrobial susceptibility testing method on isolated colonies recovered from the blood culture bottle."
MRSA-positive/SA-positive results can still be reported as such, Cepheid said.
Cepheid said that it will incorporate these new instructions in its product labeling.
Because the recall is being blamed on the rapid genetic evolution of MRSA, it would seem to raise the concern that other nucleic acid tests for infectious organisms could have a similar problem.
In fact, Cepheid's is not the first nucleic acid-based test for MRSA to be recalled by the FDA. In 2008, the BD GeneOhm PCR MRSA test was recalled because of defective reaction tubes supplied in the test kits which may have generated false-positive results.
However, in contrast "Cepheid initiated this recall because of false-negative MRSA results," an FDA spokesperson said in an e-mail to PCR Insider. Other nucleic acid tests have been recalled by the FDA in the past decade, as well, but generally due to defective instrumentation or software.
"Overall we do not see a trend for recalls with nucleic acid tests," the spokesperson added. "As with other in vitro device technologies, there is always a small probability that there may be device, or lot-to-lot reagent malfunction, or even a user error, which may result in an erroneous result. Neither the total number of recalls for nucleic acid tests, nor the fact that the root cause for each recall is quite different, suggests any common ongoing problem for nucleic acid tests for organisms such as MRSA."