Programmatic impact of using QuantiFERON®-TB Gold in routine contact investigation activities.

OBJECTIVES: To retrospectively assess the proportion of contacts tested with QuantiFERON ® -TB Gold (QFT-G) compared to the tuberculin skin test (TST) who were successfully evaluated and treated for latent tuberculosis infection (LTBI), and to assess the correlation of positive test results with measures of TB exposure.
METHODS: Contacts of culture-confirmed pulmonary TB cases reported to the San Francisco Department of Public Health between 1 March 2005 and 31 December 2007 were included.
RESULTS: Of 1291 contacts meeting the eligibility criteria, 641 (50%) were tested with QFT-G and 650 (50%) with TST. Contacts tested with QFT-G were more likely to complete evaluation (64% vs. 56%, OR(adj ) = 1.52, 95%CI 1.12-2.06). Infected contacts started (89% vs. 72%, OR(adj) = 5.18, 95%CI 2.10-14.18) and completed (70% vs. 53%, OR(adj) = 3.37, 95%CI 1.78-6.56) LTBI treatment more often in the group tested with QFT-G. Positive QFT-G results, but not positive TST results, correlated with the intensity, proximity and duration of TB exposure in foreign-born subjects.
CONCLUSION: More contacts were successfully evaluated and treated for LTBI when screened with QFT-G compared to TST. Measures of exposure correlated better with QFT-G-positive results and, therefore, appropriately identified high-risk contacts for TB prevention.