Macrolide resistance among pediatric pharyngeal Group A streptococci is high in Canada and increasing in the US

Macrolide resistance (MR) among Group A streptococci (GAS) has implications for treatment of pharyngeal and invasive infections. In Year 1 (2000-2001) and Year 2 (2001-2002) of our ongoing surveillance of pharyngeal GAS, MR rates in the United States were 4.4% and 4.3%, respectively. We now report MR rates among GAS in the US and Canada and describe national differences in emm types and MR genotypes for 2002-2003 (Year 3), 2003-2004 (Year 4), and 2004-2005 (Year 5). MR rates were higher each year in Canada than in the US but the rates appear to be converging. Resistance rates increased significantly in the US from 3.8% in Year 3 to 8.4% in Year 5. MR genotypes and the most prevalent MR emm types varied significantly between the two neighbor nations.