Positive TB test ‘not always cause for worry’
Dr. Prachi Chhimwal
Positive TB test ‘not always cause for worry’
~The belief that 40% of Indians may be infected with the bacterium is based on a ‘misunderstanding’~
Came across this interesting article published in The Hindu today.....

You have tested positive for tuberculosis (TB) but not shown any symptoms for two years. Are those germs likely to persist and make you sick years later? Most likely not, suggests a study that has combed published research from over half-a-century on the incubation period of the TB bacterium and the time it usually takes to manifest into the disease.

Globally, nearly 10 million people developed TB disease in 2017 and about 1.7 billion people, or 23% of the world’s population, are estimated to have a “latent TB infection, and are at risk of developing active TB disease during their lifetime”, according to the World Health Organisation’s Global Health Report 2018, made public last week.

Advice to high burden nations:-
The canonical belief, it emerges from the study, that 40% of Indians may be infected with the bacterium is based on a “misunderstanding” and “simply wrong,” one of the researchers involved told The Hindu. She added that countries such as India with a high disease burden would do well to focus on treating active TB cases (that is those clinically confirmed and manifesting symptoms), than trying to stamp out latent TB.

These numbers, from which India’s latent-TB burden are also derived, are based on results from the popular diagnostic tests employed — the ‘skin test’ and the Interferon Gamma Release Assay, or IGRA (a blood test) — that only indicate whether a person had generated immunity in response to TB exposure. They do not say whether the germ lies latent or will manifest into active disease. “Most of them are not latently infected. They were infected at one time, cleared the infection and may even be somewhat protected against new infection,” said Lalita Ramakrishnan, one of the study authors and Professor of Immunology at the MRC Laboratory of Molecular Biology, University of Cambridge. “In short, the statement that 40% of Indians are latently infected is simply wrong, and based on confusing immunoreactivity to TB with latent infection.”

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