The burden of latent multidrug-resistant tuberculosis

In the past 10 years, there has been renewed interest in the early phases of the natural history of tuberculosis.Estimates suggest that around 25% of the world's population could have latent tuberculosis infection,5–10% of whom will develop active disease during their lifetime(10% annually among people with HIV).Failure to implement effective tuberculosis control measures to manage latent infection threatens elimination goals.

Groups at high risk of active tuberculosis are the focus of programmatic management of latent tuberculosis infection.Once active disease is ruled out, tuberculosis preventive therapy can be offered. However, such therapy is thought to be ineffective against multidrug-resistant (MDR) strains (ie, those resistant to isoniazid or rifampicin, or both), and is thus rarely used to treat contacts of people with MDR tuberculosis.

In The Lancet Infectious Diseases, Gwenan Knight and colleagues investigated the global burden of latent tuberculosis to provide the first estimates of the prevalence of latent MDR disease. They used surveillance and survey data, estimated annual risks of infection, and informative priors for patterns of increase to develop and validate a novel cohort method to calculate this burden. Knight and colleagues estimated that around 19 million people could be latently infected with MDR tuberculosis (10% of whom were infected in 2013 and 2014—ie, the most recent 2 years included in the model), representing around 1·2% of the total burden of latent infection. Children younger than 15 years, who progress to active disease more quickly than adults and therefore are a sentinel event suggesting recent local transmission, had more than double the risk of latent MDR tuberculosis infection that adults had. These data show that transmission of MDR strains of tuberculosis is worryingly high and probably increasing, and should be urgently addressed. Knight and colleagues also estimated that, even if all tuberculosis transmission was halted, reactivation of latent disease would mean that the future burden of MDR disease would still be substantial.Their work thus clearly emphasises the need for interventions to limit both transmission of MDR tuberculosis and reactivation of latent MDR disease.

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