Use of the QuantiFERON®-TB Gold test to confirm latent tuberculosis infection in a Canadian tuberculosis clinic

SETTING: Capital Health Tuberculosis (TB) Clinic, Edmonton, Alberta, Canada. OBJECTIVE: To analyze the QuantiFERON (R)-TB Gold In-Tube test (QFT) results after implementation as a routine test for tuberculin skin test (TST) positive patients. DESIGN: From November 2004 until January 2007, patients who were TST-positive and were eligible for preventive treatment based on Canadian guidelines, were offered a QFT. RESULTS: Of 1446 TST-positive patients, only 566 (39.6%) were QFT-positive. Categorized by reason for TST testing, 43.1% of 304 contacts, 32.8% of 348 employment screens and 24.2% of 298 post secondary school screens were QFT-positive. In contrast, 59.7% of 290 immigration screens were QFT-positive. A multivariate analysis found that QFT positivity was associated with older age, larger TST size, high-incidence TB region of birth, history of TB and chest X-ray findings suggestive of previous TB. CONCLUSION: Implementation of the QFT as a secondary test for latent TB infection (LTBI) can significantly reduce the number of patients given LTBI treatment in a low-incidence country such as Canada.