Background:
Streptococcus pyogenes (StrepA) can be typed by DNA sequencing of a portion of the emm gene which encodes the M protein of the bacteria. There are over 240 emm types identified of which a small number are responsible for the majority of invasive disease cases in Alberta, Canada (current population 4.44 million). Surveillance in Alberta shows recent changes have occurred in the prevalence of specific emm types.
Methods:
Invasive StrepA (iStrepA) disease in Alberta is notifiable to Public Health authorities for case follow up. Therefore, all identified StrepA from clinical microbiology laboratories are sent to the Public Health laboratory for emm typing. This data was analyzed looking for changes in emm type prevalence.
Results:
The prevalence of emm types causing iStrepA disease has substantially changed in the last four years in Alberta, Canada. emm types frequently associated with iStrepA have decreased in prevalence. For the last year of surveillance (2021) emm types that have decreased include emm1 (0.6% of iStrepA cases), emm3 (0%), emm12 (0.6%), and emm28 (1.2%). In contrast, emm types not typically associated with iStrepA disease have increased. These include emm49 (34.3% of cases), emm74 (6.3%), emm76 (6.3%), and emm81 (17.0%).
Conclusions:
The epidemiology of iStrepA disease in Alberta, Canada has changed. This has resulted in a decrease in some of the previously more common emm types and an increase in emm types not typically associated with iStrepA disease. Surveillance such as described here is important as there are future StrepA vaccines in development are emm type based.