In TB detection, smear microscopy’s share still holds sway

Subject :Science and technology

Section: Health

Context:

According to the WHO Global TB report 2022, over 40% of 10.6 million people globally who developed TB in 2021 were not diagnosed. India along with Indonesia and the Philippines accounted for a 67% drop in the number of people with TB being diagnosed in 2020.

Sputum smear microscopy:

Sputum smear is a rapid test to detect the presence of acid-fast bacilli (AFB) but a single sputum test lacks sensitivity.
Even when people finally get tested for TB, sputum smear microscopy with about 50% sensitivity has been used for diagnosis in a majority of the cases in India, thus leading to a huge number of missed TB cases.
Drawbacks:
- Besides lower sensitivity, smear microscopy is ill-equipped to diagnose rifampicin resistance.
Way back in 2014, the WHO guidelines clearly stated that GeneXpert may be used rather than conventional microscopy and culture as the initial diagnostic test in all adults suspected of having TB.

Molecular tests for TB:

Molecular tests are not only more sensitive than smear microscopy, they also help identify rifampicin resistance at the outset.
Yet, India has been overly relying on smear microscopy for the initial diagnosis.
Even in 2015, the Joint monitoring mission report had criticised the national TB programme for heavily relying on smear microscopy and for the “slow uptake of the new molecular test”.
The rapid molecular diagnostic machines have been scaled up from 40 in 2014 to 5,090 in 2022.

India’s reliance on sputum smear microscopy for TB detection test:

As per the India TB report 2023, even last year, 77% (13.9 million) of presumptive TB cases were examined using smear microscopy and just 23% (4.1 million) with a molecular test.
The presumptive TB case examination rate (PTBER) is a good indicator of the efforts to detect and diagnose TB cases.
According to the 2019-2021 TB prevalence survey report, nearly 43% of the TB cases in the survey would have been missed if a chest X-ray was not included.

Tuberculosis (TB) cases in India:

According to the National TB prevalence survey in India 2019-2021 report, nearly 64% did not get tested for TB. It varied from 46% in the case of Kerala to 88% in Haryana.
50% of all people with bacteriologically confirmed tuberculosis have no symptoms and by the time symptoms develop, transmission has probably already occurred.
There is emerging evidence that TB may not fall under a binary of latent infection (asymptomatic and non-infectious) and active disease (symptomatic and infectious).
Instead, TB may be a spectrum of disease, including incipient and subclinical stages.
In 2020, the RNTCP was renamed as the National TB Elimination Program (NTEP) to underscore India’s goal to eliminate TB in the country by 2025, five years ahead of the Sustainable Development Goals.