[A retrospective cohort study on the risk of pulmonary tuberculosis incidence among individuals with latent tuberculosis infection in schools].

Objective

To evaluate the risk of developing pulmonary tuberculosis (PTB) among individuals with latent tuberculosis infection (LTBI) in schools and the protective effect of tuberculosis preventive treatment (TPT).

Methods

A retrospective cohort study was conducted to collect data on 15 school outbreaks that occurred in Guangdong Province from 2017 to 2021. Baseline information on tuberculin skin test (TST) or interferon-gamma release test (IGRA) was obtained during contact surveys, as well as baseline information such as TPT. The incidence of PTB between 2017 and 2022 was queried using the Chinese Center for Disease Control and Prevention Information System. Poisson regression analysis was used to compare the incidence risk of PTB in the LTBI population under different TST states at baseline. Current cases, new cases and all cases (the sum of the two) were used as dependent variables. Cox regression models were used to analyze various risk factors affecting the risk of PTB in the LTBI population and evaluate the protective effect of TPT.

Results

A total of 6 550 contacts were included in this study, of which 409 received TPT. Within 0-3 months after baseline survey, 119 cases were diagnosed as current cases [19.4‰, 119/(6 550-409)]. A total of 17 221.65 person-years of follow-up were conducted, during which 71 new cases were diagnosed (4.1/1 000 person-years, 71/17 221.65). The incidence density of PTB was 47.7/1 000 person-years, 6.6/1 000 person-years, 1.4/1 000 person-years, and 0.9/1 000 person-years, respectively, in TST strong/IGRA positive, TST moderate positive, TST generally positive, and TST and IGRA negative populations. The difference in PTB incidence density was statistically significant [likelihood ratio test LRT=153.16, P<0.001]. TPT was performed for individuals with strong TST or IGRA positivity, and the protection rate could reach 93% (HR=0.07, 95%CI: 0.02-0.23).

Conclusion

After the outbreak of the school epidemic, individuals with strong TST/IGRA positivity have a higher risk of developing PTB in the future. Targeted implementation of TPT can achieve better protection effects. In addition, the risk of developing PTB in individuals with moderate TST positivity is also worth noting.