# Responding to a protracted tuberculosis outbreak: lessons from multiple rounds of investigation in a Chinese boarding school

## TL;DR

A tuberculosis outbreak in a Chinese boarding school was studied over multiple semesters to understand transmission and improve future outbreak control.

## Contribution

The study provides insights into transmission patterns and control measures for a prolonged tuberculosis outbreak in a school setting.

## Key findings

- Most tuberculosis cases clustered in one class and were linked to a primary case with delayed diagnosis.
- Whole-genome sequencing confirmed a single transmission chain with lineage 2 strains differing by ≤12 SNPs.
- Improved screening and preventive measures are recommended to prevent future outbreaks.

## Abstract

This study analysed a multi-semester pulmonary tuberculosis (PTB) cluster outbreak in a Chinese boarding school to provide evidence for future epidemic control.

Contacts were screened via symptoms, infection tests and chest radiography. Screening expanded progressively from close contacts to same-floor contacts, then all students and staff. Whole-genome sequencing (WGS) with single nucleotide polymorphism (SNP) and bioinformatics analysis was used for lineage classification, transmission clustering (≤12 SNPs defining a cluster) and drug resistance prediction.

From 2020 to 2022, 20 students were diagnosed with PTB, half laboratory-confirmed. Most cases clustered in class 16 and were epidemiologically linked to the primary case (case 0), who had household PTB exposure. Case 0 and case 1 had diagnostic delays exceeding 3 and 6 months, respectively. WGS of five isolates (case 1, 3, 4, 9 and 10) collected over three semesters showed all belonged to lineage 2 and differed by ≤12 SNPs, confirming the same transmission chain. The infection rate in class 16 (46.34%) was significantly higher than other case classes (19.05%) and classes without cases (8.27%) (χ2 = 61.169, p < 0.001). No new cases were detected during a one-year follow-up of students involved in the outbreak after the final round of screening, nor among household contacts of all cases followed up to the present.

Lack of entry health examinations facilitated the outbreak. Delayed diagnosis, incomplete contact screening and absence of preventive treatment led to cross-semester persistence. The infection rate disparity confirms class 16 as the outbreak epicentre. Improving community case management, extending contact follow-up and enhancing cluster outbreak measures are recommended to prevent future outbreaks.