M types of group A streptococcal isolates submitted to the National Centre for Streptococcus (Canada) from 1993 to 1999

The National Centre for Streptococcus (NCS) (Canada) determined the group A streptococcal (GAS) M types of 4,760 Canadian isolates submitted between 1993 and 1999 by classic serotyping. The 10 most frequently identified M types were M1 (26.4%), M12 (9.8%), M28 (8.9%), M3 (6.8%), M4 (6.2%), M11 (4.8%), M89 (3.1%), M6 (3.0%), M2 (2.6%), and M77 (1.9%). Nontypeable isolates accounted for 15.4% of the collection. The province of Ontario submitted 51.1% of the isolates, followed by Quebec (21.2%) and Alberta (13.9%). Together, these three provinces constituted 71.3% of the Canadian population in 1996. The numbers of M types M1, M12, M28, and M3 occurred most frequently in subjects whose ages were <1 to 15 years and 25 to 45 years, as well as in the elderly (60 to 90 years). Further analysis found that the four most frequently identified M types from blood, brain, and cerebrospinal fluid were M1 (28.2%), M28 (9.2%), M12 (9.1%), and M3 (8.2%), with 13.4% of isolates being nontypeable. The four isolates from throats most frequently identified were M1 (19.5%), M12 (15.3%), M3 (8.6%), and M28 (5%) with 19.4% of isolates being nontypeable. The sic gene of a subset of M1 strains (9.5% of the M1 collection) was sequenced. Of 36 sic types identified, the four most common were sic1.01 (22.8%), sic1.02 (14.9%), sic1.135 (10.5%), and sic1.178 (9.6%). Together these four sic types further characterized nearly 60% of the M1 strains sequenced. In summary, from the years 1993 to 1999, the NCS detected 54 M types, of which 10 different M types constituted 73.5% of the collection. M1 was the most common GAS M type circulating in the Canadian population, responsible for more than a quarter of the isolates typed. The most common throat isolates differed in M-type and proportion from those of invasive isolates. Sequencing the sic gene further characterized the most common M-type serotype 1 in a fashion that may be useful for epidemiologic investigations.