Impact of interferon-γ release assay on the latent tuberculosis cascade of care: a population-based study (original) (raw)

2017, The European respiratory journal

Latent tuberculosis infection (LTBI) screening and treatment can have a significant impact on TB incidence if a high proportion of at-risk people successfully complete an adequate course of LTBI therapy [1-5]. Patient loss and dropouts occur at multiple points along the LTBI screening and treatment process, ultimately resulting in a minority of high-risk people completing LTBI therapy. To understand the public health impact of new screening and treatment strategies, we need to evaluate the impact of various interventions on the LTBI cascade of care. Interferon-γ release assay (IGRA) guidelines were introduced in British Columbia (Canada) in 2010 with implementation of both QuantiFERON-TB Gold In-Tube test (QFT; Qiagen, Germantown, MD, USA) and T-SPOT.TB test (T-Spot; Oxford Immunotec, Marlborough, MA, USA) by the British Columbia Centre for Disease Control (BCCDC) Public Health Laboratory. Provincial recommendations include the use of IGRAs as an optional test in tuberculin skin test (TST)-positive people with bacille Calmette-Guerin (BCG) vaccination history and lower risk of TB exposure and/or progression to active TB [6]. This approach uses IGRAs as a "confirmatory" test in people with positive TSTs and has been described as the "sequential approach" to LTBI testing. Sequential LTBI testing is used in several low-incidence regions, and is presented as an option in some situations by the European Centre for Disease Prevention and Control, the National Institute for Health and Care Excellence (United Kingdom), and Canadian TB guidelines [5-7]. We performed this study to examine the impact of a sequential TST-IGRA testing on LTBI outcomes in publicly funded TB clinics. We sought to compare sequential testing with the historical TST-only strategy using in routine clinical data.