Abstract:

Objective: To explore the critical value of mean diameter of induration tuberculin by skin test (TST) for the diagnosis of late tuberculosis infection (LTBI) that needs preventive medication in the treatment of tuberculosis epidemic in school. Methods: From October 2020 to October 2021, 163 students and teachers from two schools with three or more student tuberculosis patients in Jiangsu Province were selected. All the subjects were tested by TST and QuantiFERON-TB gold in-tube (QFT). Using the QFT results as the reference standard, the receiver operating characteristic curve (ROC) was used to determine the critical value of mean diameter of induration tuberculin, to diagnosis LTBI students and teachers who needed to have preventive treatment. Results: Of the 163 individuals, 79 (48.5%) were positive and 84 (51.5%) were negative in QFT. Among 132 individuals with moderate positive in TST, 62 were QFT positive (47.0% (95%CI: 38.3%-55.6%)). Of the 163 individuals, using the QFT results as the reference standard, TST had the highest diagnostic value when the induration diameter of TST was 12.5 mm, with a sensitivity of 38.0% (95%CI: 27.3%-49.6%) and a specificity of 82.1% (95%CI: 72.3%-89.6%). The area under the curve (AUC) was 0.621 (95%CI: 0.542-0.696). Among 132 individuals with moderate positive TST, using the QFT results as the reference standard, TST had the highest diagnostic value when the induration diameter of TST was 12.5 mm, with a sensitivity of 25.8% (95%CI: 15.5%-38.5%) and a specificity of 87.1% (95%CI: 77.0%-93.9%), and the AUC was 0.572 (95%CI: 0.483-0.657). Conclusion: In the treatment of tuberculosis epidemic in school if there are three or more tuberculosis cases in a class or the moderate or strong positive rate of TST is much higher than the normal range in the region, attention should be paid to the population with moderate positive TST results.

Key words: Tuberculosis, Students, Disease outbreaks, Diagnosis, Protective agents