Abstract
BACKGROUND: About 10% latent tuberculosis infections (LTBI) would progress to active tuberculosis (TB), if left prophylactic therapy. Tuberculin skin test (TST) is the most widely used method for LTBI screening in the school of China. However, for college students, the association between TST reaction size and active TB risk was unclear. METHODS: We conducted a retrospective study to assess whether the TST reaction size would predict active TB during the next two years after TST screening for college students. Multivariable Cox regression was performed to identify the size of TST reaction and other factors associated with active TB risk. RESULTS: A total of 67292 college students in Beijing, China were included in this study; 8021 (11.92%) individuals were TST positive (≥10 mm), and 3879 (5.76%) of them were strong TST positive (≥15 mm). During the two years of follow-up, 26 active TB cases were reported in 134575 person-years with an incidence rate of 19.32 (95% CI: 12.61-28.32) per 100000 person-years. The adjusted hazard ratios (HR) (95% CI) were 1.094 (0.247~4.846), 3.644 (1.188~11.179), 6.832 (2.436~19.163) and 9.768 (2.203~43.315) of cohorts with the TST reaction size intervals 5~9, 10~14, 15~20 and ≥ 20 mm, respectively, compared to cohort with interval 0~4 mm. Besides, the adjusted HR (95% CI) was 3.593 (1.354~9.537) of males compared to females. CONCLUSIONS: This study indicated that the risk of active TB increased in college students when the TST reaction size was ≥10 mm, and males had a higher risk compared to females.