Social-network analysis of a tuberculosis outbreak

January 01, 0001

Social-network analysis of a tuberculosis outbreak

An outbreak of tuberculosis occurred over a 3-year period in a medium-size community in British Columbia, Canada. The results of mycobacterial interspersed repetitive unit-variable-number tandem-repeat (MIRU- VNTR) genotyping suggested the outbreak was clonal. Traditional contact tracing did not identify a source. The authors used whole-genome sequencing and social-network analysis in an effort to describe the outbreak dynamics at a higher resolution. They sequenced the complete genomes of 32 Mycobacterium tuberculosis outbreak isolates and 4 historical isolates (from the same region but sampled before the outbreak) with matching genotypes, using short-read sequencing. Epidemiologic and genomic data were overlaid on a social network constructed by means of interviews with patients to determine the origins and transmission dynamics of the outbreak.

They found: "Whole-genome data revealed two genetically distinct lineages of M. tuberculosis with identical MIRU-VNTR genotypes, suggesting two concomitant outbreaks. Integration of social-network and phylogenetic analyses revealed several transmission events, including those involving ‘superspreaders.’ Both lineages descended from a common ancestor and had been detected in the community before the outbreak, suggesting a social, rather than genetic, trigger. Further epidemiologic investigation revealed that the onset of the outbreak coincided with a recorded increase in crack cocaine use in the community."

The authors concluded: "Through integration of large-scale bacterial whole-genome sequencing and social-network analysis, we show that a socioenvironmental factor — most likely increased crack cocaine use — triggered the simultaneous expansion of two extant lineages of M. tuberculosis that was sustained by key members of a high-risk social network. Genotyping and contact tracing alone did not capture the true dynamics of the outbreak."

This study shows significant advance in epidemiological methods of investigation that will be useful for future studies.

For the full abstract, click here.

N Engl J Med 364:730-739, 24 February 2011
© 2011 to the Massachusetts Medical Society
Whole-Genome Sequencing and Social-Network Analysis of a Tuberculosis Outbreak. Jennifer L. Gardy, James C. Johnston, Shannan J. Ho Sui, et al. Correspondence to Patrick Tang: [email protected]

Category: R. Respiratory, Z. Social Problems. Keywords: tuberculosis, epidemiology, crack cocaine, genotyping, genome sequencing, social network analysis, journal watch.
Synopsis edited by Dr Linda French, Toledo, Ohio. Posted on Global Family Doctor 22 March 2011

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