More than 19 million people around the globe are infected with one of the most complex forms of dormant tuberculosis, threatening efforts to control the fatal disease, researchers have warned.

In the first study to estimate the number of people living with latent multi-drug resistant tuberculosis (MDR-TB), published in Lancet Infectious Diseases, experts found that three people in every 1,000 carry the hard-to-treat bacteria – a “worryingly high” figure that “threatens elimination goals”.

TB is one of the deadliest diseases in the world, killing roughly 1.7 million people and infecting 10 million every year.

But almost a quarter of the world’s population is unwittingly living with the latent form of the disease – meaning Mycobacterium tuberculosis bacteria are lying inactive inside their body, with the potential to trigger symptoms at any time.

Eradicating latent TB is central to efforts to control the ancient illness, as between five and 10 per cent of those with the dormant infection go on to develop active symptoms.