Updated on 30 July 2012
Tuberculosis (TB) is the leading cause of death worldwide. According to the WHO, India accounts for the one-fifth of global TB problem with about 800,000 lakh of new infectious cases each year, resulting in two deaths-per-three minutes. With the advent of extrapulmonary TB (EPTB), HIV and MDR-TB the situation has worsened. In most of the developing countries, including India, sputum smear microscopy is still a backbone of TB diagnosis. It is less sensitive and can miss half of the pulmonary TB cases, which otherwise proves to be a potential reservoir for transmitting the infection from individual-to-individual. There is an overwhelming need for improving TB diagnostics in India through the use of cost-effective and patient-friendly methods owing to large genetic diversity among the target population.
Improved diagnostic tests such as rapid mycobacterial culture and nucleic acid amplification (NAA) tests are available in high-income countries but are often too expensive and complex for routine use by TB control programs in resource-constrained TB-endemic regions. The Xpert MTB/RIF (by Cepheid, US), recently endorsed by the WHO, is rapid and highly sensitive for detection of TB and drug resistance. However, this new technology is costly, preventing its use in many areas. Accurate, rapid, inexpensive, simple diagnostic tests are urgently needed for TB care and control.
In India, serological tests to detect antigens or antibodies to M. tuberculosis specific components by using cocktails of excretory or secretory protein antigens, Ag 85 complex antigens, Hsp 65 antigen, RD1 antigens have also been developed. These groups have been extensively working on over the past couple of decades and showed promise of these tests to diagnose TB through various literatures. Several biomolecules are available at our doorstep worth capable of delivering the diagnostics from concepts to the deliveries. Over the past decade, the involvement of agencies, such as stop TB Partnership's New Diagnostics working group, the WHO, TDR, Foundation for Innovative New Diagnostics (FIND), has led to the resurgence of interest in the development of new diagnostics. However, breakthrough on development of simple, rapid and cost effective diagnostic kit for mass is still evading the health administrators for effective TB control.
While serological tests work well for several infectious diseases, existing serological tests for TB (both ELISA and rapid lateral flow tests) are not accurate or consistent enough to be useful, as shown by a 2007 meta-analysis1 and confirmed by an independent evaluation of 19 commercial rapid tests by the WHO the following year2. However, evidence from these studies was not translated into policy at that time. In 2010, the WHO recognized this widespread problem and convened an expert group to formulate a policy. The expert group considered an updated meta-analysis of test and concluded that commercial serological tests remain inconsistent and inaccurate. The WHO in its first-ever negative policy recommendation called on governments to immediately ban on commercial tests to detect pulmonary TB and extra pulmonary TB.