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.
“Latent TB is a significant reservoir of disease,” Dr Gwen Knight, assistant professor at the London School of Hygiene and Tropical Medicine and lead author of the report, told The Telegraph.
“Our research suggests that in the future the level of latent MDR-TB will rise, which could overwhelm our targets to control TB and is only going to make this disease a bigger threat on the world stage,” she said.
The study, based on estimates from mathematical models, broke the data down by region and age.
Children under 15 were twice as likely to carry latent MDR-TB than adults – a concern because the dormant infection more commonly triggers active symptoms among this age group, who are less likely to access treatment.
The Western Pacific and European regions had the highest prevalence of the hard-to-treat latent TB, with China, India, Russia and Indonesia identified as having the largest number of infected individuals.
“Those four countries are all places in the world where there’s a lot of poverty and TB transmission, so it was not unexpected,” said Dr Knight, adding that all four nations also had high MDR-TB rates.
“But in Eastern European countries MDR-TB is not necessarily driven by poverty – it has more to do with a history of TB drug exposure,” she added.
Drug resistance is a growing global problem across a range of diseases, but MDR-TB is particularly difficult to combat – and only 25 per cent of active MDR-TB patients are diagnosed.
Some strains of TB are totally resistant to all available drugs, while others require 18 month-long treatment programmes, which only half of patients complete.
“We need better tests to detect latent MDR-TB, as we currently can’t know what strain somebody has,” said Dr Knight. “We need better diagnostics so we can tailor therapy and ensure we’re giving people drugs which will work.”
In a comment piece accompanying the article, Alberto Garcia-Basterio, Helen Jenkins and Moleboleng Rangaka said that latent the MDR-TB figures were “worryingly high and probably increasing, and should be addressed urgently.
“The TB epidemic will not be ended without tackling people who are latently infected,” they said.
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