The study of tuberculosis outbreak in a high school-Shanghai, China, 2017-2018

Aim To investigate the attack rate of active tuberculosis (TB) cases and detection rate of latent tuberculosis infection (LTBI) cases, and to identify possible factors contributed to the outbreak in a high school. Subject and methods We analyzed the investigation data of 35 teachers and 108 students, including active TB cases and their close contacts. The symptoms inquiry, tuberculin skin test (TST), and chest X-ray/CT scan were conducted in the close contact screening. We did variable-number-of-tandem-repeat genotyping and whole-genome sequencing of isolates. Results The time interval between the onset of symptoms and diagnosis was 36 days. The total attack rate of active TB was 7.69% (11/143), with a class attack rate of 27.78% (10/36) among students. The genetic differences between any two available isolates were less than 5 SNPs. Approximately 15.38% (22/143) of persons were LTBI cases, and the total detection rates of LTBI for students and teachers were 7.40% (8/108) and 40% (14/35), respectively. Being in the same class as the index case resulted in a significantly higher risk of being diagnosed with active TB (P = 0.0001, RR = 18.51, 95%CI (2.44,140.42)) and either LTBI and MTB infection (RR = 14.40, RR = 16.46, respectively) compared with that of students in a non-index class. Conclusion The case-finding delay should be reduced to prevent the spread in classes and schools. Effective surveillance and regulated screening for student contacts should be strengthened in schools to detect infections early.