Population-based surveillance of invasive pyogenic streptococcal infection in a large Canadian region.

Pyogenic streptococci are a major cause of invasive infection. This study presents the results of a population-based laboratory surveillance for invasive pyogenic streptococcal infections among residents of the Calgary Health Region (population 1 million) between 1 July 1999 and 30 June 2004. The overall annual incidence rate was 18.65/100,000 population, with isolates belonging to the Streptococcus milleri group forming the most important aetiology (incidence of 8.65/100,000 population). Invasive infection with groups A, B, G and C streptococci occurred at annual rates of 4.27, 3.13, 1.83 and 0.41/100,000 population, respectively. There was a close relationship between increasing age and development of an invasive pyogenic streptococcal infection, and the incidence of infection was higher among males than among females. Differences in the seasonal occurrence and focus of infection occurred between the different groups.