Epidemic of group A Streptococcus M/emm59 causing invasive disease in Canada.

BACKGROUND: The incidence of invasive group A Streptococcus (GAS) disease can vary over time and geographic region, possibly reflecting the population's susceptibility to particular strains but also variation in the predominant M/emm types. Canadian surveillance documented an epidemic of an uncommon M/emm59 type from 2006 to 2009.
METHODS: Invasive GAS isolates are submitted by Public Health Laboratories in Canada to the National Centre for Streptococcus for M/emm typing. Patient age, sex, geographic location, and the anatomical source of isolate are provided with the isolate. When it was recognized that M/emm59 strains were increasing in prevalence, clinical information was collected on M/emm59 cases captured in Alberta and compared with cases of other M/emm types occurring in this province.
RESULTS: From January 2006 through December 2009, 539 (13.0%) of 4150 invasive GAS cases were identified as M/emm59: 164 from British Columbia, 146 from Alberta, 62 from Saskatchewan, 82 from Manitoba, 68 from Ontario, 14 from Quebec, 1 from New Brunswick, 1 from Newfoundland, 1 from Yukon, and 1 from Nunavut. The predominant clinical presentation was bacteremia (45.0%) followed by cellulitis (41.4%). Compared with concurrent cases of invasive GAS disease caused by all other M/emm types, identified risk factors for M/emm59 disease were alcohol abuse (odds ratio [OR], 2.3; 95% confidence interval [CI], 1.4-3.8), homelessness (OR, 2.0; 95% CI, 1.2-3.4), hepatitis C virus infection (OR, 2.0; 95% CI, 1.1-3.5), and illicit drug use (OR, 1.7; 95% CI, 1.0-3.0).
CONCLUSIONS: Western Canada has witnessed the rapid emergence of a rare GAS strain causing invasive disease predominately in a select population of disadvantaged persons.