Comparative agreement between tuberculin skin test and QuantiFERON-TB Gold In-Tube across different levels of exposure in a college-based tuberculosis outbreak.

Background: Optimal intervention thresholds for students in college TB outbreaks remain debated. Tuberculosis preventive treatment (TPT) is recommended for tuberculin skin test (TST) induration greater than 15 mm. The possibility of TPT recommendation for individuals with TST medium or weak positivity in the context of recent exposure, particularly with close contact with TB, is not entirely clear. Methods: The study used a cross-sectional design and included a 1-year follow-up of participants after preventive treatment. TST and QuantiFERON-TB Gold In-Tube test (QFT) were used among close contacts of the tuberculosis cases from a college. Since individuals with a strongly positive TST result undergo TPT directly, close contacts with a TST less than 15 mm were further assayed with QFT. TST and QFT were compared based on TB exposure, which was classified as inside or outside classes with TB cases. Student's Results: A total of 1,182 close contacts of TB cases during an outbreak were administered TST. A total of 175 (14.8%, 175/1,182) students had a strongly positive test result (≥15 mm). QFT was performed on the remaining 1,007 students, of whom 85 (8.4%, 85/1,007) tested positive. Among individuals with TST negative indurations (<5 mm), low positivity (5-9 mm), and medium positivity (10-14 mm), QFT positivity was 2.9% (7/237), 5.4% (3/55), and 10.5% (75/715), respectively. The rates of QFT positivity varied with increased TST levels ( Conclusion: TST showed better concordance with QFT when close contacts were under intense and frequent TB exposure, and a 10 mm result for TST would be a potential recommendation for preventive treatment in close contacts with high exposure to TB transmission.