Laboratory identification of tuberculosis outbreak in a middle school in Beijing

  Objective   To analyze the characteristics of the Mycobacterium tuberculosis isolates from a tuberculosis (TB) outbreak in a middle school in Beijing, from October 2018 to January 2019 with Laboratory detection techniques and provide evidence for the tracing, prevention and control of the TB epidemic.

  Methods   A laboratory test was conducted for the index case and 203 close contacts, including M. tuberculosis antibody detection, γ-interferon detection, sputum smear and culture, as well as the identification, molecular typing and cluster analysis of positive strains.

  Results   According to the gold standard for culture positive in laboratory, a total of 6 TB cases, including the index cases, were identified. In the culture-positive group, the immunological examination showed that the positive rate of M. tuberculosis antibody was 50%, and the positive rate of γ-interferon was 66.7%. After DNA extraction of the 6 positive strains, all the strains were identified as M. tuberculosis by multi-loci PCR. At the same time, and the 6 strains were detected by 12 loci variable number tandem repeat sequence analysis (MLVA) and the spacer (Spoligotyping) oligonucleotide method. The results showed that 5 strains belonged to Beijing genotype, and 1 strain had no result. It was found that 4 strains had same VNTR pattern of 12 loci, and one strain had 1.6 variant in Qub11a locus, another strain showed a difference of one copy number at ETR-A and MIRU27, but the copy numbers at other sites were same.

  Conclusion   The 6 positive isolates identified in this laboratory were all M. tuberculosis, and 5 strains belonged to Beijing genotype. MLVA typing analysis indicated that 4 strains shared high homology, suggesting the possibility of recent transmission and the necessity of further sequencing analysis.