Reemergence and Amplification of Tuberculosis in the Canadian Arctic

J Infect Dis. 2015 Jun 15;211(12):1905-14. doi: 10.1093/infdis/jiv011. Epub 2015 Jan 9.

Abstract

Background: Between November 2011 and November 2012, a Canadian village of 933 persons had 50 culture-positive cases of tuberculosis, with 49 sharing the same genotype.

Methods: We performed Illumina-based whole-genome sequencing on Mycobacterium tuberculosis isolates from this village, during and before the outbreak. Phylogenetic trees were generated using the maximum likelihood method.

Results: Three distinct genotypes were identified. Strain I (n = 7) was isolated in 1991-1996. Strain II (n = 8) was isolated in 1996-2004. Strain III (n = 62) first appeared in 2007 and did not arise from strain I or II. Within strain III, there were 3 related but distinct clusters: IIIA, IIIB, and IIIC. Between 2007 and 2010, cluster IIIA predominated (11 of 22 vs 2 of 40; P < .001), whereas in 2011-2012 clusters IIIB (n = 18) and IIIC (n = 20) predominated over cluster IIIA (n = 11). Combined evolutionary and epidemiologic analysis of strain III cases revealed that the outbreak in 2011-2012 was the result of ≥6 temporally staggered events, spanning from 1 reactivation case to a point-source outbreak of 20 cases.

Conclusions: After the disappearance of 2 strains of M. tuberculosis in this village, its reemergence in 2007 was followed by an epidemiologic amplification, affecting >5% of the population.

Keywords: Mycobacterium tuberculosis; infectious disease outbreaks; molecular epidemiology; transmission; whole genome sequencing.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Adult
  • Arctic Regions
  • Canada / epidemiology
  • Communicable Diseases, Emerging / epidemiology*
  • Communicable Diseases, Emerging / microbiology
  • Disease Outbreaks*
  • Female
  • Genome, Bacterial
  • Genotype
  • Humans
  • Male
  • Mycobacterium tuberculosis / classification
  • Mycobacterium tuberculosis / genetics
  • Mycobacterium tuberculosis / isolation & purification
  • Phylogeny
  • Sequence Analysis, DNA
  • Tuberculosis / epidemiology*
  • Tuberculosis / microbiology
  • Young Adult