High pharyngeal carriage rates of Streptococcus pyogenes in Dunedin schoolchildren with a low incidence of rheumatic fever

Aim. To document the incidence and type distribution of Streptococcus pyoge nes in a group of Dunedin children throughout the 1997 school year. Methods. The 780 children recruited from ten primary schools had their thro ats swabbed on each reporting of pharyngitis. Additional pharyngeal swabbin gs were obtained monthly from a representative subset of these children, re ferred to as group 1. All swab samples were plated on CNA-P, a blood agar m edium that facilitates detection of haemolytic streptococci, S. pyogenes is olates were classified according to the RFLP patterns of PCR products of th eir emm genes (ERP typing). Representative isolates of each ERP pattern wer e also emm-typed, a sequence typing method that correlates with serological M-typing. Results. 28% of the group 1 children were found to carry S. pyogenes for mo re than two months. This carriage rate is similar to that previously detect ed in Dunedin and Waikato Schoolchildren, but is higher than that generally reported in other countries. Although the predominant S. pyogenes types de tected-in Dunedin are similar to those in North Island populations, some of the types frequently associated with North Island cases of rheumatic fever and glomerulonephritis were absent or isolated infrequently from the Duned in children. Conclusion. The high pharyngeal carriage-rates of S. pyogenes in Dunedin sc hoolchildren, without the concomitant increased occurrence of post-streptoc occal sequelae observed in North Island populations may, in part, be due to a relatively lower occurrence of the M-types most commonly implicated in t hese diseases.