New TB test shows promise in early, accurate diagnosis
London: A new test developed recently to detect tuberculosis seems to be very effective in accurately tracing the disease early, according to a study carried out in several TB-prone countries, including India.
The study involving over 6,600 people in six countries such as India, South Africa, Peru, Azerbaijan, the Philippines and Uganda found that the `Xpert MTB/RIF` test has been highly accurate in detecting the disease and its multi-drug resistant (MDR) form.
The study, published online in the medical journal `The Lancet`, showed that the cartridge-based, automated diagnostic test can be used effectively in resource-poor
settings to rapidly diagnose those infected.
It is believed that the test, which was jointly developed by US-based Cepheid Inc and Switzerland`s the Foundation for Innovative New Diagnostics (FIND), can potentially cut delays in diagnosis and treatment of the disease, reducing TB-related morbidity and mortality significantly.
"Our findings suggest that decentralised MTB/RIF test implementation is feasible and could lead to an improvement in tuberculosis care and control," the authors said.
"Any improvement will require increased detection of tuberculosis and multidrug-resistant-tuberculosis to coincide with scale-up of first-line, and more importantly, second-line treatment," they added.
For the study, Dr Catharina Cora Boehme of FIND and colleagues recruited 6,648 people having cough for at least two weeks at selected health centres in those six countries.
The authors compared one-off direct MTB/RIF testing in nine microscopy laboratories adjacent to study sites with the standard TB diagnostic methods of two sputum smears and one cultures, dependent on site and drug-susceptibility testing.
A single direct MTB/RIF test detected 933, or 90 percent, of 1033 culture-confirmed TB cases, compared with 699, or 67 per cent, of 1041 for microscopy.
While MTB/RIF test sensitivity (true positive rate) was 77 per cent in smear-negative, culture-positive patients, it`s found 99 per cent in specificity or the true negative rate.
Sensitivity for rifampicin -- a bactericidal antibiotic drug -- resistance was also found to be 94 per cent (236 of 250) and specificity was 98 per cent (796 of 810).
Unlike microscopy, MTB/RIF test sensitivity was not significantly lower in patients with HIV co-infection.
Moreover, the median time for detection of tuberculosis via the MTB/RIF test was 0 days, compared with one day for microscopy, 30 days for solid culture and 16 days
for liquid culture.
Similarly, the median time for the detection of MDR was 20 days for line-probe assay and 106 days for conventional drug susceptibility testing.
It was also found that use of the MTB/RIF test reduced median time to treatment for smear-negative tuberculosis from 56 days to five days.
"Our study confirms the sensitivity of the MTB/RIF test for smear-positive and smear-negative tuberculosis, when undertaken in routine microscopy centres, and showed reduced, but good performance for detection of rifampicin resistance,"
said the authors.
"Furthermore, we suggest the MTB/RIF test can provide a substantially reduced time to detection and treatment for smear-negative tuberculosis," they said.
However, they added that it needs to established whether early and appropriate treatment after MTB/RIF testing can cut tuberculosis-related morbidity and mortality and its effect on transmission.
First Published: Tuesday, April 19, 2011, 00:00
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