Tuberculosis Transmission at Household and School among Adolescents in Guangxi, China

Abstract

Objective 1: To evaluate the association between history of exposure to tuberculosis (TB) in households and in classrooms and being newly diagnosed index TB case at school. Methods: From November 2016 to October 2017, a prospective matched case-control study was conducted among adolescent students using passively identified index cases from the TB surveillance system and healthy controls matched by county, school type, sex, age and ethnicity. Contacts in households and classrooms of index cases and of the controls were investigated. Results: Matched tabulation of 117 case-control pairs revealed exposure to TB in the household as a strong risk factor (odds ratio (OR) = 28.11, 95% confidence interval (CI) = 3.31, 238.5). A higher proportion of index cases had newly detected active TB (current TB) in the classroom than the healthy controls (12.0% versus 1.7%). The risk of being an index case or healthy control on exposure to previous and current TB in the classroom was not significantly different. Family heads with lower education level increased the risk of a student being an index TB case in the school (OR = 3.05, 95% CI = 1.1, 8.44). Lower family income also corresponded to the student having a greater risk of being an index TB case. Conclusion: Our findings suggest that previous exposure to TB in the household could lead a child to develop TB at school, further spreading TB to classmates. Objective 2: To quantify the tuberculosis (TB) risk attributable to classrooms and dormitory rooms exposed to index cases. Methods: Adolescent school contact investigations were conducted for every reported index TB case and similar investigations were conducted in selected community-control classes. Results: A total of 6,512 contacts of 117 index TB cases and 6,480 classmates of 117 controls were investigated. There were 26, 19 and 2 new active TB cases detected among classmates/non-roommates of index cases, classmates/ roommates of index cases and control classmates, respectively. Compared with control contacts, the adjusted relative risk (RR) and population attributable fraction (PAF) for being a classmate/non-roommate of the index case increased the risk of active TB infection to 15.21 times (95% CI: 2.75, 84.14) and 51.68%, respectively. The adjusted RR and PAF for being a classmate/roommate of the index case was 52.86 (95% CI: 9.02, 309.7) and 39.66%. Being a classmate/roommate significantly increased the risk of TB compared to a classmate/non-roommate of the index case (RR=3.48, 95% CI: 2.00, 6.05). Conclusion: All available data from this study indicates the need to emphasize TB prevention in dormitory rooms, although the classroom should not be neglected. Objectives 3: To estimate the strength of association between latent tuberculosis (TB) infection (LTBI) and exposure to TB in the classroom in different school types (middle school and high school). Method: School contact investigation was conducted for every reported index TB case in the classrooms of middle and high schools, and similar contact investigations were conducted in selected comparable control classrooms. The QuantiFERON TB Gold In-Tube assay was performed following a positive tuberculin skin test for latent TB infection. Results: 6,153 classmates of 110 newly diagnosed index TB cases and 6,026 students of 110 control classes were included. Without TB exposure in the classroom, a lower LTBI rate was detected among students in middle schools (0.19%) compared to high schools (0.56%). Middle school students exposed to an index TB case in the classroom had an increased odds of LTBI (OR=3.07, 95% CI: 1.85, 5.1); in the high school classroom, the risk increased by 51% (OR=1.51, 95% CI: 1.04, 2.2). Conclusion: Low baseline LTBI prevalence but high odds ratio from TB exposure in middle school indicates the importance of TB infection prevention in this group, although the high schools should not neglected.