The FDA has cleared the Cepheid Xpert MTB/RIF Assay to help physicians determine if patients with suspected tuberculosis (TB) can be removed from airborne infection isolation. This expanded use allows healthcare providers to use one or two negative Xpert MTB/RIF Assay test results to help them determine whether a patient showing signs and symptoms of pulmonary TB should continue to be kept in a hospital airborne isolation room.
TB is caused by Mycobacterium tuberculosis complex (MTB-complex) and usually attacks the lungs. Many people carry the MTB-complex bacteria without ever developing active disease. Common signs and symptoms of active TB include a bad cough lasting three weeks or longer, chest pain, coughing up blood, weakness, fatigue and weight loss.
Current CDC TB infection control guidelines recommend placing a patient suspected of having active TB in an airborne infection isolation room. CDC recommends keeping that person isolated until clinical and laboratory information, including acid-fast bacilli (AFB) smear testing of three sputum (mucus coughed up from the lungs) specimens, each collected eight to 24 hours apart, show that the patient is unlikely to have contagious TB.
The MTB/RIF test is a nucleic acid amplification test, different from a smear in that it can test specifically for the DNA of the mycobacteria that cause TB. This test can detect TB better than the smear test, and can detect TB even when the smear test may be negative. Because the MTB/RIF test can detect TB better than the smear, results from one or two MTB/RIF tests can be used in the decision to remove patients from isolation.
“The revised labeling states that the results from one or two consecutive negative tests using the MTB/RIF will strongly predict the results that would be obtained from AFB smear testing of three sputum specimens for the TB bacteria,” said Alberto Gutierrez, Ph.D., director of the Office of In Vitro Diagnostics and Radiological Health at FDA’s Center for Devices and Radiological Health. “This information, along with other patient clinical data, can be valuable in deciding whether a patient can spread TB to other people and whether continued airborne isolation is necessary.”
“We are encouraged that a quicker option for detecting contagious TB is now available to assist in determining whether patients must remain in isolation,” said Philip LoBue, M.D., director of the CDC’s Division of Tuberculosis Elimination. “The test may make it possible for some patients to be released from hospital isolation sooner, freeing up limited medical resources and removing restrictions on patients’ movements and interactions. While this test can assist health care providers in making important decisions regarding isolation, it does not replace the continued need for culture testing to ensure patients with TB are accurately diagnosed and treated.”
In July 2013, the FDA granted marketing authorization of the MTB/RIF through the de novo classification process, a regulatory pathway for some low- to moderate-risk medical devices that are not substantially equivalent to an already legally marketed device. The FDA granted marketing authorization of the MTB/RIF test for the detection of bacteria that causes active TB, and if present, to determine if the bacteria contain genetic markers that make them resistant to rifampin, an antibiotic drug used to treat TB.
The recent FDA action was based on a large clinical study showing the ability of one or two consecutive negative results from the MTB/RIF test to correctly identify patients who would also test negative for the TB bacteria by AFB smear testing of sputum. A single negative MTB/RIF test result predicted the absence of MTB-complex on AFB smears 99.7 percent of the time, and two consecutive negative MTB/RIF test results predicted the absence of the bacteria 100 percent of the time.
The decision whether one or two tests are necessary is based on the specific patient being tested and hospital guidelines. Decisions regarding whether to remove a patient from isolation should always be based on all the information available about the patient, not just test results.
The CDC cautions the MTB/RIF test may not detect all patients with active TB, so it is important that healthcare workers also continue to follow current CDC guidelines to collect consecutive sputum specimens for TB culture testing, even if results from MTB/RIF testing are negative.
Approximately 10 – 15 percent of patients with active TB in the lung cannot be detected by the MTB/RIF test, so culture testing remains essential for proper diagnosis. These patients usually do not require isolation but need to be treated if culture results show they have active TB. Culture is also necessary for testing to ensure that the correct drugs are used when patients are diagnosed with TB.
Today’s labeling change does not affect current medical practice guidelines for Mycobacterium tuberculosisinfection control, but opens the door for further study and data collection opportunities which may influence future guidelines. These guidelines are developed, reviewed and modified by groups other than the FDA.
The Xpert MTB/RIF Assay is manufactured and marketed by Cepheid of Sunnyvale, Calif.
