Mycobacterium tuberculosis Beijing family: Analysis of the epidemiological and clinical factors associated with an emerging lineage in the urban area of Milan

•The Beijing family of M. tuberculosis is an emerging lineage in the area of Milan.•Beijing strains affect mainly young foreign-born patients.•Beijing strains are associated with MDR, but not with HIV infection.•Constant prevalence over time of the founder Beijing sublineages.

The Mycobacterium tuberculosis Beijing genotype raises major concern because of global spreading, hyper-virulence and association with multi-drug resistance (MDR). The aims of the study were to evaluate role of Beijing family in the epidemiological setting of Milan and to identify predictors associated with the spreading of this lineage. Overall 3830 TB cases were included. Beijing family accounted for 100 isolates (2.6%). Prevalence grew from 1.7% to 5.4% in the period 1996-2009. Foreign origin increased significantly the risk of having a Beijing strain: the greatest risk was observed among patients coming either from China [AOR = 57.7, 95%CI (26.3-126.8)] or from Former Soviet countries [AOR = 33.9, 95%CI (12.8-99.6)]. Also MDR was independently associated with Beijing family [AOR = 2.7, 95%CI (1.3-5.8)], whereas male gender and younger age only approximated the statistical significance [p 0.051 and p 0.099, respectively].However, the percentage of cases attributable to MDR strains decreased over time, both in the Beijing group and in the non-Beijing group.97 isolates were grouped in 37 sub-lineages: MT11, MT33 were predominant. Beijing family is an emerging lineage in Milan. Origin from countries like China and Ukraine and MDR are significantly associated with Beijing. The broad range of the sub-lineages reflects the recent dynamics of the migration flows to our area. This scenario can prelude to a constant increase in the spreading of Beijing strains in the near future.