Group A Streptococcus emm gene types in pharyngeal isolates, Ontario, Canada, 2002-2010

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.

Figure 1

Distribution of group A Streptococcus (GAS) emm types collected in Toronto, Ontario, Canada, 2002–2010. Thirty-four GAS emm types with <10 isolates each (≈0.3% of total) comprise the “other” category. Line graph showing cumulative percentage is superimposed with percentage scale shown on right.

Figure 2

Annual frequency of emm89 isolates among patients with group A Streptococcus pharyngitis, Toronto, Ontario, Canada, 2002–2010.

Figure 3

Frequency of emm3 strains among patients with group A Streptococcus pharyngitis and invasive disease, Ontario, Canada, 2002–2010, excluding 2004–2005. Black line indicates yearly frequency of invasive emm3 isolates; red line indicates emm3 frequency among pharyngeal isolates.

Figure 4

Frequency of emm89 strains among patients with group A Streptococcus pharyngitis and invasive disease, Ontario, Canada, 2002–2010, excluding 2004–2005. Black line indicates yearly frequency of emm89 among invasive disease isolates; red line indicates frequency of emm89 among pharyngeal isolates.