Group A streptococcal pharyngitis is still common, and the peak incidence occurs in school-aged children. However, the incidence in adults is higher than expected, and the number of secondary cases in families may be an important factor when considering the potential benefits of treatment.
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% CI, 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.
These data suggest that the emergence of GAS strains with increased virulence is not the main factor responsible for the surge in GAS-related infections. The prevalence of particular emm types, RAPD profiles, or superantigen genes in invasive disease may simply indicate widespread transmission of these strains in the population, rather than a particular ability to cause disease.
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