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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 stant.We also sought to determine whether different Beijing sublineages have distinct phenotypic characteristics.We conducted a population-based molecular epidemiologic study in six provinces in China from 2009 to 2010.We analyzed data and specimens from culture-confirmed pulmonary tuberculosis patients.Each patients isolate was genotyped using 16-loci variable number of tandem repeats (VNTR) and 6 single nucleotide polymorphisms (SPNs).ResultsBy 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 versus retreatment patients.We identified six sublineages of Beijing strains in the study population.The modem sublineage of Beijing strains were more likely than the ancient sublineages to be clustered (odds ratio,2.27,P <.001).