Abstract: Objective To determine the relationship between tuberculin reactivity and tuberculosis incidence,and to propose the tuberculin reactivity criteria for chemoprophylaxis. Methods A 4-year follow-up to fresh college students at different level of tuberculin reactivity was conducted,the corelation of tuberculin reactivity with tuberculosis risk and disease time were analyzed,and the difference in the incidence of subjects at different level of reactivity towards chemoprophylaxis was compared. Result Tuberculin testing and the 4-year follow-up were conducted for 26 543 eligible subjects.Tuberclusis risks for the subjects with tuberculin reactivity of 0～4 mm,5～9 mm,10～14 mm,15～19 mm and more than 20 mm or with blister/papula were 12.97/100000,13.32/100000,50.21/100000,167.56/100000 and 250.21/100000 respectively.For the subjects with 0～4 mm and 5～9 mm tuberculin reactivity,tuberclusis risks were very low in the first 2 years,and increased in the 3 rd and 4th year,while for the subjects with 15～19 mm and more than 20 mm or with blister/papula tuberculin reactivity,tuberclusis risks were very high in the first 2 years,but decreased with time goes on.Calculating the tuberculosis incidence for different tuberculin reactivity criteria when increasing 1 mm interval or above,showed that tuberculosis incidence were simialr and high for all those with 15 mm or above on tuberculin reactivity criteria.The tuberculin reactivity criteria at 15 mm or above covered 80.8% patients,and the case-finding efficiency was at highest level. Conclusion Tuberculosis risk coorelated with tuberculin reactivity positively,espacially in the first 2 years.PPD reacter at the 15 mm or above had significantly high risk to develop tuberculosis,and it can cover more than 80% patients with the the case-finding efficiency at highest level.Therefore,tuberculin reactivity criteria at more than 15 mm or with blister/papula was more reasonable for chemoprophylaxis.

Key words: Tuberculosis/prevention and control, Tuberculin testing, Incidence