Saurabh Gupta, Head of Strategy, Mylab Discovery Solutions explains how latent TB management and control can help in elimination of TB in India
India registers largest number active TB cases globally, but this number is rather small compared to burden of latent TB infection (TBI). Latent TB is a state of persistent immune response to stimulation by M. tuberculosis antigens with no evidence of clinically manifest TB disease. Most infected people have no signs or symptoms of TB but are at risk for developing TB disease. Nearly 35-40 crores Indian population have TBI, of which 26 lakhs people are likely to develop tuberculosis (TB) disease annually.
The problem is that from this pool of infected but asymptomatic persons, most patients of TB disease will be notified and the studies show 5–10 per cent of all those infected will develop TB disease over the course of their lives. And most of the infected people usually become active TB within first 2 years after initial infection. The risk for TB disease after infection depends on several factors, the most important being immunological status. It is estimated that the risk increased by more than 25 times among contacts of active TB patients compared to general populations.
Several studies show 75 per cent of people who develop TB disease after contact with a patient of active TB are estimated to do so within one year of TB diagnosis of the index patient and 97 per cent within two years. Prevention of TB disease by treatment of TBI is a critical component of the National Strategic Plan 2017-25 for Ending TB in India by 2025. It is considered that if these patients can be identified and treated, the rate of decline in TB incidence will increase from 2.5 per cent at present to 10 per cent required annually.
Until recently, there has been no gold standard test to diagnose TBI or predict progression to TB disease among those infected. With new tests approved for detecting latent TB, this could change significantly. Excluding TB disease is a critical step before starting preventing therapy for treatment of latent TB, and confirming TBI before starting TPT may increase the certainty that individuals targeted for TPT would benefit from it. Tests also enhance confidence of providers as well as recipients to start TPT.
Having a way of diagnosing latent TB and better drug regimen such as 3HP (rifapentine and isoniazid) will help us prevent infected patients to be active TB patients. And this could really make all the difference.