New rapid TB tests could reduce mortality

Drug-resistant forms of TB are harder and expensive to treat and pose a major threat to global public health, experts say

Three new tests for more rapidly diagnosing drug-resistant forms of tuberculosis (TB) could help make treatments more effective and reduce mortality, a study conducted in three countries, including India has found.

Drug-resistant forms of TB are much harder and more expensive to treat and represent a major threat to global public health, experts say.

“Our study shows that TB testing that once took two to three months can now be done in as little as a day,” said co-author Richard Garfein, professor at the University of California, San Diego School of Medicine.

“This means we can put people on the right medications sooner, spare them the toxic effects of drugs that are ineffective and prevent the development of drug resistant forms of TB that can occur when the wrong medications are given,” said Garfein.

TB remains one of the world's deadliest infectious diseases, causing (or contributing to) an estimated 1.5 million deaths in 2013, according to the World Health Organisation.

TB is also the leading killer of people who have HIV, researchers said.

For the study, sputum (a mixture of saliva and mucus coughed up from the lungs) from 1,128 study participants at TB clinics in countries including India, Moldova and South Africa were examined using three rapid tests for detecting drug-resistant forms of TB. Two of these tests use molecular techniques to look for genetic mutations in the pathogen's eoxyribonucleic acid (DNA) that confer resistance to antibiotics.

The third test employs a low-cost and easy-to-use version of the standard bacterial culture technique, making it suitable for resource-limited community clinics and hospitals. An estimated  95 per cent of TB deaths globally occur in low- and middle-income countries.

The results from the rapid tests were then compared to the reference standard technique for detecting resistance to seven of the most important anti-TB drugs. These comparisons showed that all three rapid assays accurately identified resistance to first- and second-line oral antibiotic treatments (isoniazid, rifampin, moxifloxacin and ofloxacin).

Further, according to researchers they were less accurate but still very good at detecting resistance to injectable antibiotics (amikacin and capreomycin) typically administered to those with multi-drug resistant TB.

The rapid tests performed poorly in detecting resistance to only one drug, the injectable antibiotic kanamycin, which is also used for treating multi-drug resistant TB.

The study also documented the time it took to obtain results. The molecular techniques showed themselves to be superior, with a mean time of 1.1 days for both DNA testing methods; 14.3 days for the rapid culture method; and 24.7 days for the reference standard test.

The study was published in the journal PLOS ONE.