Two US studies, one that followed 64 children aged 6 to 12 years at a single elementary school in Philadelphia for four years (1955-59), and another that followed 125 children aged 5 to 15 years at an elementary school in Pittsburgh for four years (1998-2002), have revealed the incidence of pharyngeal infection with Streptococcus pyogenes (Group A beta haemolytic streptococcus =GAS) in young children.  

Two much smaller NZ studies have revealed the prevalence of S. pyogenes in throat swabs, from 789 school children, aged 11 years, in five Waikato schools during May-June 1977, and from 780 school children, aged 5-11 years, in ten Dunedin schools during February-November 1997. The findings from these four studies tell a consistent story. The incidence of new S. pyogenes infection is about 20-45% per year. About half of these new infections are asymptomatic or are associated with atypical symptoms. Asymptomatic colonisation following new infection commonly lasts many months, and in many children persists for up to a year. The consequence of relatively frequent acquisition of infection, and of subsequent prolonged asymptomatic colonisation, is that at any time throughout the year approximately 20-50% of children will have S. pyogenes pharyngeal infection.