Mycobacterium tuberculosis Beijing strains favor transmission but not drug resistance in China

Abstract

Background: The Mycobacterium tuberculosis Beijing strains are widespread globally. We aimed to determine whether Beijing strains in China are more likely than other strains to spread, and whether they are more likely to become drug resistant. We also sought to determine whether different Beijing sublineages have distinct phenotypic characteristics.

Methods: We conducted a population-based molecular epidemiologic study in 6 provinces in China from 2009 to 2010. We analyzed data and specimens from culture-confirmed pulmonary tuberculosis patients. Each patient's isolate was genotyped using 16-loci variable number of tandem repeats and 6 single-nucleotide polymorphisms.

Results: By genotyping, 75.0% (1031/1375) of the strains of M. tuberculosis were Beijing strains. Beijing strains were more likely than non-Beijing strains to be in a genotypic cluster (odds ratio, 2.40, P < .001), and were significantly associated with younger age (P(trend) < .05). There was no significant difference in the proportion of Beijing strains and non-Beijing strains that were drug resistant, even when stratified by new vs retreatment patients. We identified 6 sublineages of Beijing strains in the study population. The modern sublineage of Beijing strains were more likely than the ancient sublineages to be clustered (odds ratio, 2.27, P < .001).

Conclusions: Beijing strains of M. tuberculosis were significantly associated with genotypic clustering, reflecting recent transmission, and younger age, but were not associated with drug resistance. Future studies of Beijing family strains should avoid assuming and attributing characteristics to the entire family and should assess strains of specific sublineages and/or settings.

Figure 1.

Map of China showing the distribution of the tuberculosis patients whose isolates of Mycobacterium tuberculosis were included in the study. The selected study field sites were Pingguo county, Guangxi Province; Wusheng county, Sichuan Province; Weishi county, Henan Province; Songjiang District, Shanghai; Fei county, Shandong Province; and Wuchang county, Heilongjiang Province. The markers on the map indicate the relative location of the 6 study sites. The star represents the national capital, Beijing city.