Molecular Epidemiology of Tuberculosis in British Columbia, Canada – A 10-Year Retrospective Study

Abstract

Background

Understanding regional molecular epidemiology allows for the development of more efficient tuberculosis (TB) prevention strategies in low-incidence settings.

Methods

We analyzed 24-locus Mycobacterial Interspersed Repetitive Units-Variable Number of Tandem Repeats (MIRU-VNTR) genotyping for 2,290 Mycobacterium tuberculosis (Mtb) clinical isolates collected in the province of British Columbia, Canada (2005–2014). Laboratory data for each isolate was linked to case-level clinical and demographic data. These data were used to describe the molecular epidemiology of TB across the province.

Results

We detected >1,500 distinct genotypes across the four major Mtb lineages, reflecting BC's diverse population. Disease site and clustering rates varied across lineages, and MIRU-VNTR grouped the 2,290 isolates into 189 clusters (2–70 isolates/cluster) with an overall clustering rate of 42.4% and an estimated local transmission rate of 34.1%. Risk factors for clustering varied between the Canadian- and foreign-born. Canadian-born individuals had increased odds (OR 7.8, 95%CI:6.2–9.6) of belonging to a genotypic cluster, although nearly one-quarter of clusters included both Canadian- and foreign-born individuals. Large clusters (≥10 cases) occurred more frequently within the Mtb Euro-American lineage, and individual-level risk factors associated with belonging to a large cluster included being Canadian-born (adjusted OR [aOR] 3.3, 95%CI:2.3–4.8), residing in a rural area (aOR 2.3, 95%CI:1.2–4.5), and drug use (aOR 2.0, 95%CI: 1.2–3.4).

Conclusions

While tuberculosis in BC largely arises through reactivation of latent TB in foreign-born persons, locally transmitted infections occur in discrete populations with distinct disease and risk factor profiles, representing groups for targeted interventions.