Assay for Pulmonary Tuberculosis and Rifampicin Resistance Reviewed

An automated test that can detect both tuberculosis (TB) and rifampicin resistance, generally within two hours after starting the test, with minimal hands-on technical time has been systematically reviewed.

The assay purifies and concentrates Mycobacterium tuberculosis bacilli from sputum samples, isolates genomic material from the captured bacteria by sonication, and subsequently amplifies the genomic DNA by polymerase chain reaction (PCR).

The review carried out by scientists at the Liverpool School of Tropical Medicine (UK) and experts from other institutions, included 27 unique studies and integrated 9 new studies that involved 9,557 participants. Sixteen studies (59%) were performed in low- or middle-income countries.

The main aims of the review were to assess the diagnostic accuracy of the assay Xpert MTB/RIF (Cepheid, Sunnyvale, CA, USA) for pulmonary TB (TB detection), where Xpert MTB/RIF was used as both an initial test replacing microscopy and an add-on test following a negative smear microscopy result. Another aim was assess the diagnostic accuracy of Xpert MTB/RIF for rifampicin resistance detection, where Xpert MTB/RIF was used as the initial test replacing culture-based drug susceptibility testing (DST).

As an initial test replacing smear microscopy, Xpert MTB/RIF pooled sensitivity was 89% and pooled specificity was 99% in 22 studies, with 8,998 participants: 2,953 confirmed TB, 6045 non-TB. As an add-on test following a negative smear microscopy result, Xpert MTB/RIF pooled sensitivity was 67% and pooled specificity was 99% in 21 studies, with 6,950 participants. In comparison with smear microscopy, the assay increased TB detection among culture-confirmed cases by 23% in 21 studies with 8,880 participants. For rifampicin resistance detection, Xpert MTB/RIF pooled sensitivity was 95% in 17 studies, with 555 rifampicin resistance positives and pooled specificity was 98% in 24 studies, with 2,411 rifampicin resistance negative. Among 180 specimens with nontuberculous mycobacteria (NTM), Xpert MTB/RIF was positive in only one specimen that grew NTM.

The managing editor of the Cochrane Infectious Diseases Group, said, “Xpert MTB/RIF may be useful in many countries, particularly in low- and middle-income countries where TB is prevalent, as it does not require advanced laboratory facilities or expert staff. The tests are expensive, so current research evaluating the use of Xpert MTB/RIF in TB programs in high TB burden settings will help evaluate how this investment may help start treatment promptly and improve patient health.” The review was published on January 21, 2014, in the journal the Cochrane Review.

Related Links:
Liverpool School of Tropical Medicine
Cepheid