Cost-effectiveness of the NICE guidelines for screening for latent tuberculosis infection: the QuantiFERON-TB Gold IGRA alone is more cost-effective for immigrants from high burden countries.

NICE (National Institute for Health and Clinical Excellence) guidelines for new entrant tuberculosis (TB) screening recommend chest x ray (CXR) for immigrants from countries with TB incidence >40/10(5), and tuberculin skin test (TST) for people with normal CXR from very high TB prevalence countries. A revised screening policy using first-line QuantiFERON-TB Gold (QFT) in high risk immigrants was piloted in 2007. Initially, TST was offered to immigrants from countries with TB incidence 200-339/10(5), and QFT to those from countries with incidence >340/10(5). When increased resources became available, all immigrants from countries with TB incidence >200/10(5) had QFT. Those with positive QFT were invited for CXR. 1336 immigrant were invited for screening, with a 32% attendance rate. 280 patients had QFT, of which 38% were positive, with <2% being indeterminate. Using the NICE approach, the cost of screening these 280 immigrants would be pound 13,346.75 ( pound 47.67 per immigrant) and would identify 83 cases of latent TB infection (LTBI). Using first-line QFT followed by CXR the cost was pound 9781.82 ( pound 34.94 per immigrant) and identified 105 cases of LTBI. The cost to identify one case of LTBI following NICE guidelines would be pound 160.81 and using the present protocol was pound 93.16. For immigrants from high risk countries QFT blood testing followed by CXR is feasible for TB screening, cheaper than screening using the NICE guideline and identifies more cases of LTBI.

Use of QuantiFERON-TB Gold test in the investigation of unexplained positive tuberculin skin tests.

OBJECTIVES: To investigate the use of new gamma-interferon (IFN-gamma)-based blood tests to determine whether or not a higher-than-expected proportion of positive tuberculin skin tests (TSTs) were due to tuberculosis infection. STUDY DESIGN: When an unexpectedly high proportion of children in a high school in Leeds were found to have positive TSTs, a cohort study was undertaken based on blood tests and long-term follow-up of the affected children. IFN-gamma-based blood tests are reported to be more specific for tuberculosis infection than TSTs. METHODS: One hundred and ninety children, aged 13-14 years, were screened and 28 (15%) had a positive TST. None had any known risk factor for tuberculosis infection. Parental consent was requested for testing with QuantiFERON-TB Gold (Cellestis, Carnegie, Victoria, Australia). Active cases of tuberculosis with any possible connection to the school or the children were sought through the routine diagnosis and reporting service over the next 36 months. RESULTS: Consent was given for 26 children with Heaf Grade 2 results to be tested using QuantiFERON-TB Gold, and blood was obtained from 24 of these children. All tested negative. None of these children developed active tuberculosis, and no cases of active tuberculosis were identified with any connection to the children or the school. CONCLUSION: QuantiFERON-TB Gold testing appeared to identify false-positive TSTs correctly in this group. This supports the recent recommendation to use IFN-gamma-based blood tests in people with positive TSTs to confirm or refute the diagnosis of tuberculosis infection.