In March, the FDA approved Xpert EV (Enterovirus) Assay, a new test designed for the rapid detection of viral meningitis. By identifying an enterovirus in a patient's CSF, the test eliminates the possibility of bacterial meningitis, which is potentially fatal and less common than viral infection, although it shares many of the same symptoms. Enteroviruses, which are single-stranded RNA viruses found in respiratory secretions and stools of infected people, are the culprit behind nearly 90 percent of all viral meningitis cases.
The test, which was developed by Cepheid of Sunnyvale, CA, uses a reverse-transcription real-time polymerase chain reaction (RT-PCR) process to concentrate and amplify the RNA of enteroviruses, the viral genetic material, in CSF.
Contrary to typical culture-based tests for meningitis that take three or more days for results, the Xpert EV test delivers results in less than three hours and does not require a specialized lab. These two features are the major advantages of the test, said Kenneth Tyler, MD, a neuroinfectious disease expert and Reuler Lewin Family Professor of Neurology at the University of Colorado Health Sciences Center in Denver. He added that the test is completely safe.
The FDA based the decision on an unpublished study submitted by Cepheid. The multisite study at six institutions tested 255 patient samples and demonstrated high specificity and sensitivity: 96.3 percent of patients who tested positive had viral meningitis, and 97.2 percent of patients who tested negative did not have viral meningitis, according to a company spokesperson.
Dr. Tyler said that “PCR tests are generally quick to run, so the timeframe for an initial result may not be unrealistic.”
“Most academic medical centers and major hospitals are already using CSF RT-PCR for enteroviral RNA in patients with suspected meningitis,” he added. “This Xpert EV test may be valuable and will likely be used in community and smaller hospitals lacking laboratories that are regularly performing CSF PCR testing.”
Dr. Tyler emphasized that further tests should be done to confirm the reported sensitivity and specificity of the Xpert EV test. He pointed out that similar tests are being studied to detect bacterial meningitis. These tests “amplify genes common to many groups of bacteria (such as those encoding ribosomal RNA subunits) or genes encoded by individual bacterial genes. One of the more common bacterial PCR-based tests is one for diagnosis of tuberculous meningitis.”