Objective To analyze the relationship between the visit intervals of indicator cases and the risk of clustered tuberculosis outbreaks in schools.

Methods A total of 623 indicator cases of pulmonary tuberculosis involved in the pulmonary tuberculosis epidemic in Guangzhou city, Guangdong province from September 2023 to September 2024 were included for analysis. Restricted cubic splines (RCS), unconditional logistic regression analysis, and receiver operating characteristic curve (ROC) were used to evaluate the relationship between the visit intervals of indicator cases and the risk of clustered tuberculosis outbreaks in schools.

Results Among 623 tuberculosis indicator cases included in this study, 66 cases were clustered with high-risk outbreaks, and 557 cases were clustered with low-risk outbreaks or had no correlation. The differences in visit interval 41.00（12.00, 104.00）d vs 7.00（0.00, 17.00）d and positive rate of pathogenic examination (69.70% VS 46.14%) were statistically significant between two groups (Z/χ² = –37.401, 13.108, P < 0.05). When the visit intervals of positive indicator cases in etiological examination exceeded 14 days or that of negative cases exceeded 8 days, the risk of pulmonary tuberculosis outbreaks in schools showed a linear increasing trend. For every 1 day increase in the visit interval, the possibility of high risk outbreaks in schools increased by 15.50% (OR = 1.155, 95%CI: 1.050–1.680, P < 0.05). When the visit intervals were analyzed by ternary, it was found that with the extension of visit interval, the risk of clustered pulmonary tuberculosis outbreaks in schools increased (Z = 12.520, P < 0.05). The ROC curve analysis showed that the threshold for predicting the high concentration risk of pulmonary tuberculosis in schools based on the visit interval was 23 days, AUC was 0.918, 95%CI = 0.829 to 0.964.

Conclusions The extended visit intervals of indicator cases may be a key early warning indicator for high-risk clustered outbreaks of pulmonary tuberculosis in schools.