Abstract
Group A Streptococcus (GAS) is a human-adapted pathogen that causes a variety of diseases, including pharyngitis and invasive infections. GAS strains are categorized by variation in the nucleotide sequence of the gene (emm) that encodes the M protein. To identify the emm types of GAS strains causing pharyngitis in Ontario, Canada, we sequenced the hypervariable region of the emm gene in 4,635 pharyngeal GAS isolates collected during 2002-2010. The most prevalent emm types varied little from year to year. In contrast, fine-scale geographic analysis identified inter-site variability in the most common emm types. Additionally, we observed fluctuations in yearly frequency of emm3 strains from pharyngitis patients that coincided with peaks of emm3 invasive infections. We also discovered a striking increase in frequency of emm89 strains among isolates from patients with pharyngitis and invasive disease. These findings about the epidemiology of GAS are potentially useful for vaccine research.
Highlights
Group A Streptococcus (GAS) is a human-adapted pathogen that causes a variety of diseases, including pharyngitis and invasive infections
To determine how common allelic variation was in the Toronto GAS population, we examined the number of alleles for each emm type found in specimens from pharyngitis patients in Toronto
GAS pharyngitis strains in Canada, we identified a similar pattern of emm type distribution as reported in previous surveys and observed that strains of a relatively few emm types dominate
Summary
Group A Streptococcus (GAS) is a human-adapted pathogen that causes a variety of diseases, including pharyngitis and invasive infections. We discovered a striking increase in frequency of emm strains among isolates from patients with pharyngitis and invasive disease These findings about the epidemiology of GAS are potentially useful for vaccine research. Sizeable outbreaks can be caused by strains of a single emm type or of a small number of emm types Overall, this combination of factors results in a complex epidemiologic situation for GAS pharyngitis. Knowledge of the rate and patterns of emergence of distinct emm types and their alleles may be critical for understanding how GAS may “escape” the immune response generated by a vaccine based on the amino-terminus of M protein. We examined the temporal change in emm types in pharyngitis cases and compared this distribution with data from a comprehensive population-based study of GAS emm types that were causing invasive infections in Ontario. We studied the emm types causing pharyngitis in multiple geographic locations across the province of Ontario in 2009 and 2010
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