Objective: The objective of this study was to determine the incidence, transmission, carriage, and risk factors for group A streptococcal pharyngitis in school-aged children and their families.
Methods: A 16-month, prospective, family-based cohort study was undertaken from August 2001 through December 2002 in Melbourne, Australia. A total of 202 families (853 people) with at least 1 child aged 3 to 12 years were randomly selected from 3 primary care practices across suburban Melbourne to collect surveillance data for acute group A streptococcal pharyngitis, including serology for index and secondary cases and intermittent carriage data. Cohort retention was 97% for 16 months.
Results: The incidence of acute sore throat, group A streptococcal swab-positive pharyngitis, and serologically confirmed group A streptococcal pharyngitis was 33, 13, and 8 per 100 child-years, respectively, for school-aged children (5-12 years) and 60, 20, and 15 per 100 family-years, respectively. Sore throat was less common in adults than children, but adults with sore throat were as likely as children to have group A streptococcal culture-positive or serologically proven pharyngitis. In families who had a primary case, 43% had at least 1 secondary case, and in family members who were at risk, 13% contracted a secondary case. The spring, summer, and winter carriage rates for children were 13%, 8%, and 16%, respectively, and for adults the rate was 2% across all seasons.
Conclusions: 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.