The role of expanded close contact screening in the tuberculosis outbreak at a school in China

Tuberculosis (TB) outbreaks in confined settings such as schools pose significant public health challenges due to the potential for rapid transmission among closely interacting individuals. In December 2018, a senior high school student in Shenzhen City, China, was diagnosed with etiological positive TB, prompting an investigation that extended until November 2024. This study aimed to analyze the outbreak's characteristics, identify its causes, and provide insights for timely identification and management of similar clusters.

The confirmed, clinically diagnosed, and suspected cases of TB were identified according to the "Tuberculosis diagnosis WS288-2017" criteria. Epidemiological investigations of TB cases included close contact screening via symptom assessment, TST, and chest radiography. Moderately TST-positive contacts underwent IGRA confirmation for preventive therapy eligibility, while MIRU-VNTR genotyping of culture-positive isolates delineated transmission networks. The Chi-square test or Fisher's exact test was employed to analyze changes in TST positivity rates and differences in TB incidence rates.

A total of six TB cases were detected in the high school, with five screenings conducted over the study period. Misdiagnosis caused a near-three-month delay from symptom onset to confirmed TB in the index case. Among the five newly diagnosed patients, four were in the same class as the index case, and one was in an adjacent class. These two classes are located on the middle horizontal line of the "B"-shaped teaching building. For the indicated case's class, the positive rate of TST in the second screening (35.85, 95% CI: 23.49-19.25%) was significantly higher than in the first screening (8.93, 95% CI: 3.33-20.37%) (χ² = 11.493, p < 0.001). MIRU-VNTR genotyping of four clinical isolates identified concordant non-Beijing strains with matching profiles at 11/12 loci (excluding VNTR3232), demonstrating a single transmission chain.

This outbreak was a cluster epidemic driven by misdiagnosis, poor ventilation, and insufficient routine prevention measures. Establishing long-term close-contact monitoring and secondary screening is crucial for identifying infections missed during the initial window period, thereby mitigating the spread of TB in similar settings and improving outbreak management strategies.