Author(s): Deanne Langlois-Klassen 1 , 2 , * , Dennis Kunimoto 3 , L. Duncan Saunders 1 , Linda Chui 4 , 5 , Jody Boffa 2 , Dick Menzies 6 , Richard Long 1 , 2 , 3
Since first being reported in 1995 (Beijing isolates) and 1996 (strain W) , , the Beijing lineage of Mycobacterium tuberculosis (also referred to as the East Asian lineage or Lineage 2) has garnered much attention in international tuberculosis literature. The largest genotype family of M. tuberculosis , Beijing strains account for 13% of strains globally and dominate the M. tuberculosis epidemiology in some geographic areas , . In the Western Pacific countries of China, Japan, South Korea and Vietnam, 54-92% of M. tuberculosis case isolates are Beijing strains , -. While other countries are only now experiencing an emergence of Beijing lineage strains , -, China has had high endemic levels of these strains for at least 60 years .
Active tuberculosis disease (TB) resulting from infection with Beijing strains has frequently been associated with TB outbreaks , , antituberculosis drug resistance , , , , treatment failure  and relapse -. Of particular concern is the association between Beijing strains and multidrug-resistant TB (MDR-TB) , , . Beijing strains also appear to have an enhanced ability to circumvent immunity induced through bacille Calmette-Guérin (BCG) vaccination, potentially resulting in a selective advantage of these strains in populations with high rates of BCG vaccination -.
In contrast, other studies have found no significant associations between Beijing strains and either BCG vaccination status  or various presentations of TB , , , -. This inter-study variability may result from the heterogeneous distribution of Beijing sublineages; programmatic differences in TB control; inherited and acquired host factors; socioeconomic circumstances; chance; and other factors -. Furthermore, little clarity is afforded by evidence of genotypic diversity within the M. tuberculosis species because it remains inconclusive as to whether or not genotypic diversity meaningfully influences the outcome of infection in vivo . The bottom line - the epidemiologic significance of Beijing lineage strains in the human population remains largely ambiguous.
Contradictory evidence within the Beijing literature and the often limited generalizability of studies make it difficult to foresee whether the emergence of Beijing lineage strains in high-income immigrant-receiving countries with low TB incidence (hereafter referred to as immigrant-receiving countries for brevity) poses an increased public health threat. This study sought to determine if the Beijing lineage of M. tuberculosis strains was associated with more high risk presentations of active TB than other strains in Canada, a country with one of the highest levels of immigration per capita internationally and in which a quarter of the foreign-born population has originated from the Western Pacific , . A secondary objective was to determine if Beijing disease presentation varied in relation to patients' age or population group.
Study approval was obtained from the University of Alberta Health Research Ethics Board. The need for patient's informed consent was waived by...