Novel Perspectives on Foreign-born Tuberculosis: Trends, Targets, and Transmission.

摘要

Immigrant-receiving countries like Canada must meet the challenge of tuberculosis (TB) in their foreign-born populations. One puzzling question is why, despite fluctuating levels of immigration from high incidence source countries, only modest variations in foreign-born TB incidence have been reported for decades. An additional concern is the disproportionate reactivation of latent TB infection (LTBI) in certain groups within this population. Despite these factors, routine screening for LTBI has not been widely implemented, primarily due to concern regarding cost-effectiveness. Another issue related to foreign-born TB is the potential importation of hypervirulent strains and/or strains with increased transmissibility. It is frequently speculated that the Beijing family of strains is included in this category. If true, TB resulting from Beijing strains could impact national TB control efforts.;This thesis aimed to (i) explain the relative constancy of TB incidence in the foreign-born in Canada by examining the trends in TB incidence among immigrant groups; (ii) identify high-yield target groups for routine screening for LTBI; and (iii) determine whether Beijing strains constitute an increased public health threat relative to other genotypes in Alberta, Canada in terms of infectiousness, drug-resistance and transmission.;These investigations found that relative constancy in foreign-born TB incidence is explained by a complex convergence of factors, including annual immigration levels, age at arrival, country of birth, and time since arrival. Consequently, immigrants ≤ 2 years post-arrival who were aged 15-35 years at arrival and born within countries with TB incidence rates >50/100,000 population were recommended as high-yield targets for the screening for LTBI. In Alberta, Beijing strains had similar disease presentations as non-Beijing strains apart from the former having significant associations with polyresistant-TB and multidrugresistant TB as well as an association of borderline significance with respiratory TB. Beijing strains also had no greater of an association with recent transmission than non-Beijing strains in Alberta.;The high global prevalence of TB, the emergence of extensively and totally drug-resistant TB, and unprecedented levels of human migration indicate that immigrant-receiving countries will be challenged by TB in their foreign-born populations for the foreseeable future. Serious consideration must be given to the implementation of effective screening strategies.