Increased genetic diversity of the Mycobacterium tuberculosis W-Beijing genotype that predominates in eastern China

- VNTR-MIRU typing is a reliable method for analyzing M. tuberculosis transmission in relatively closed populations.
- VNTR3820 shows having the highest discriminatory power and allelic diversity.
- Endogenous relapse is main source of TB cases in eastern China.
- Migration has played an important role in the recent transmission of the W-Beijing family of M. tuberculosis.

ObjectivesTo determine the genetic diversity of Mycobacterium tuberculosis (M. tuberculosis) strains in a Chinese population predominately infected with strains of the W-Beijing family.MethodsA cross-sectional study was conducted in three counties of eastern China. M. tuberculosis strains were collected at TB clinics, and patients were interviewed by trained physicians at the time of TB diagnosis. RD105 and RD181 were used to identify W-Beijing and modern W-Beijing strains, respectively, while seven-locus variable numbers of tandem repeat-mycobacterial interspersed repetitive unit (VNTR-MIRU) analysis was employed to differentiate the genotypes of these strains.ResultsOf 441 strains studied, 394 (89.3%) were identified as W-Beijing family strains; of them, 299 were modern W-Beijing strains. VNTR-MIRU identified 409 genotypes from 426 strains, including 395 unique patterns and 14 clusters. Ancestral W-Beijing strains were more likely to be clustered (OR = 1.32, 95%CI: 0.58-2.97) compared to modern W-Beijing strains. The proportions of clustered strains were 14.6%, 4.2% and 0% at sites Funing (FN), Deqing (DQ) and Yinzhou (YZ), respectively. Of the seven MIRU loci, VNTR3820 was found to have the highest discriminatory power and allelic diversity.ConclusionsVNTR-MIRU typing appears to be a reliable method for analyzing M. tuberculosis transmission in relatively closed populations. The low clustering proportions indicate that endogenous relapse may be a main source of TB cases in eastern China. Furthermore, our results indicate that migration has played may play an important role in the recent transmission of the W-Beijing family of M. tuberculosis.