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From latent to active TB: are IGRAs of any use?
  1. Wei Shen Lim
  1. Correspondence to Dr Wei Shen Lim, Nottingham University Hospitals NHS Trust, City Hospital Campus, Nottingham NG5 1PB, UK; weishen.lim{at}nuh.nhs.uk

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In May 2014, the World Health Assembly approved the WHO End TB Strategy which set ambitious targets for the elimination of tuberculosis (TB), including a 95% reduction in TB deaths and a 90% reduction in TB incidence by 2035.1 In December 2015, WHO Guidelines for low-TB-burden countries for the management of latent Mycobacterium tuberculosis (MTB) infection (LTBI) were published in support of the WHO End TB Strategy.2 A major focus of these guidelines is the identification of people with LTBI and the provision of chemoprophylaxis to prevent the development of active TB in those infected.

Latent TB infection is defined as a state of persistent bacterial viability, immune control and no clinical evidence of active TB.3 ,4 There is no direct test to diagnose LTBI. Instead, LTBI is recognised by the presence of measurable immune sensitisation to MTB as identified by a positive result to either tuberculin skin testing or an interferon-γ release assay (IGRA).5 In many high-income and upper-middle-income countries with low TB incidence, IGRAs currently play an integral part in screening programmes for LTBI. A clear understanding of the predictive value of IGRAs for the development of active TB disease is therefore necessary.

In 2012, Rangaka et al6 published a meta-analysis of longitudinal studies that assessed the positive and negative predictive values (PPVs and NPVs) of IGRAs for future active TB. Fifteen studies (6 from Europe) with a combined sample …

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