INVASIVE GROUP-A STREPTOCOCCAL INFECTIONS IN ONTARIO, CANADA

Background Several reports suggest that the incidence of invasive grou p A streptococcal infections, including streptococcal toxic shock synd rome and necrotizing fasciitis, is increasing. Methods During 1992 and 1993 we conducted prospective, population-based surveillance of invas ive group A streptococcal disease in Ontario, Canada. We reviewed clin ical and laboratory records, searched for secondary cases of invasive disease, and cultured specimens from household contacts. Results We id entified 323 patients with invasive group A streptococcal infections, for an annual incidence of 1.5 cases per 100,000 population. The rates were highest in young children and the elderly. Fifty-six percent of the patients had underlying chronic illness. Risk factors for disease included infection with the human immunodeficiency virus, cancer, diab etes, alcohol abuse, and chickenpox. The most common clinical presenta tions were soft-tissue infection (48 percent), bacteremia with no sept ic focus (14 percent), and pneumonia (11 percent). Necrotizing fasciit is occurred in 6 percent of patients, and toxic shock in 13 percent. T he mortality rate was 15 percent overall, but it was 29 percent among those over 64 years of age (P<0.001) and 81 percent among those with t oxic shock (P<0.001). Fourteen percent of the cases were nosocomial, a nd 4 percent occurred in nursing home residents, often in association with disease outbreaks. Invasive disease occurred in 2 household conta cts of patients with infection, for an estimated risk of 3.2 per 1000 household contacts (95 percent confidence interval, 0.39 to 12 per 100 0). Conclusions The elderly and those with underlying medical conditio ns are at greatest risk for invasive group A streptococcal disease, to xic shock, and necrotizing fasciitis. Invasive streptococcal infection is associated with a substantial risk of transmission in households a nd health care institutions. (C) 1996, Massachusetts Medical Society.