Background: In 2010, Winnipeg, Canada, experienced a doubling of invasive pneumococcal disease (IPD) rates, with a significant increase in the number of cases due to Streptococcus pneumoniae serotype 12F, which previously had accounted for very few cases each year.
Methods: All serotype 12F IPD cases reported between September 2009 and January 2011 were reviewed. Pulsed-field gel electrophoresis (PFGE) and multilocus variable number tandem repeat analysis (MLVA) were conducted on all isolates. PFGE and MLVA patterns identified several possible clusters. Additional interviews were conducted to obtain information on risk factors and outcomes.
Results: Between September 2009 and January 2011, 169 cases of IPD were identified. The number of IPD cases due to 12F serotype increased sharply from about 3-4 cases per year (6% of IPD cases) in 2007-2009 to 28 (29%) in 2010. All 12F isolates belonged to a single sequence type (ST218), and they were generally susceptible to penicillin and fluoroquinolones but not to erythromycin. Compared with cases caused by other serotypes, patients with serotype 12F were more likely to be homeless, reside in low-income inner-city communities, and engage in substance abuse, including intravenous and crack cocaine use. Subclusters identified using MLVA had even higher rates of homelessness and substance use.
Conclusions: An immunization campaign targeting high-risk groups was undertaken with pneumococcal polysaccharide vaccine, and subsequently rates of serotype 12F decreased. To our knowledge, this is the largest documented community outbreak of serotype 12F IPD and the first report of an outbreak of IPD serotype 12F in a marginalized urban population in Canada.
Keywords: homeless; invasive pneumococcal disease; outbreak; serotype 12F; surveillance.
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