Abstract:

Objective This study aims to explore detection methods of latent Mycobacterium tuberculosis infection (LTBI) in close contacts of active tuberculosis patients among college students in Shanghai, to provide evidence for screening of close contacts of active tuberculosis patients in schools in areas with low prevalence of tuberculosis in China. Methods According to the different levels of reported incidence of tuberculosis in 2019 in Shanghai, we choose Pudong New Area, Songjiang District and Minhang District as study sites, close contacts of college active tuberculosis patients among the freshman/sophomore in three districts were continuously recruited as study subjects. In addition to routine screening methods, a questionnaire and interferon gamma release assay (IGRA, by QFT-GIT) were conducted in the subjects. Of the 767 close contacts who finished the baseline questionnaire, 747 had both TST (by BCG-PPD) and QFT results. The positive rate, cost effectiveness and screening efficiency of TST, QFT and TST-QFT combined tests, as well as the influencing factors of the inconsistent of TST and QFT test results were analyzed. Results The positive rates were 5.0% (37/747) by QFT, 17.1% (128/747) by TST and 4.0% (30/747) by TST-QFT combined test. The cost per case of LTBI detected by QFT alone was the highest (RMB 6218.9 yuan), while that by the combined use of TST-QFT reduced to 51.4% (RMB 3023.0 yuan). One LTBI could be found among 24.9 subjects by TST-QFT (numbers needed to screen (NNS) was 24.9), screening was more effective in those with no BCG scar (NNS=7.3), BMI<18.5 (NNS=5.5) and smokers (NNS=14.8). Multivariate logistic regression analysis showed that inconsistent of TST and QFT detection (TST(-)/QFT(+) vs. TST(-)/QFT(-): aOR (95%CI)=10.99 (1.76-68.54); TST(+)/QFT(-) vs. TST(-)/QFT(-): aOR (95%CI)=1.98 (1.13-3.49)) were more likely to be found in smokers. Conclusion When IGRA could not be widely used for LTBI detection, the TST-IGRA two-step method was recommended, especially in those without BCG scar and BMI<18.5. It could reduce the screening cost and improve the efficiency to a certain extent, while smokers are recommended to use IGRA test directly.

Key words: Tuberculosis,pulmonary, Students, Infection, Population surveillance