The epidemiology of invasive group A streptococcal disease in Victoria, Australia

Objective: To estimate the incidence and severity of invasive group A streptococcal infection in Victoria, Australia. Design: Prospective active surveillance study. Setting: Public and private laboratories, hospitals and general practitioners throughout Victoria. Patients: People in Victoria diagnosed with group A streptococcal disease notified to the surveillance system between 1 March 2002 and 31 August 2004. Main outcome measure: Confirmed invasive group A streptococcal disease. Results: We identified 333 confirmed cases: an average annualised incidence rate of 2.7 (95% Cl, 2.3-3.2) per 100 000 population per year. Rates were highest in people aged 65 years and older and those younger than 5 years. The case-fatality rate was 7.8%. Streptococcal toxic shock syndrome occurred in 48 patients (14.4%), with a case-fatality rate of 23%. Thirty cases of necrotising fasciitis were reported; five (17%) of these patients died. Type 1 (23%) was the most frequently identified emm sequence type in all age groups. All tested isolates were susceptible to penicillin and clindamycin. Two isolates (4%) were resistant to erythromycin. Conclusion: The incidence of invasive group A streptococcal disease in temperate Australia is greater than previously appreciated and warrants greater public health attention, including its designation as a notifiable disease.