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Abstract
Aim. To document the incidence and type distribution of Streptococcus pyogenes in a group of Dunedin children throughout the 1997 school year.
Methods. The 780 children recruited from ten primary schools had their throats swabbed on each reporting of pharyngitis. Additional pharyngeal swabbings were obtained monthly from a representative subset of these children, referred to as group 1. All swab samples were plated on CNA-P, a blood agar medium that facilitates detection of haemolytic streptococci. S. pyogenes isolates were classified according to the RFLP patterns of PCR products of their emm genes (ERP typing). Representative isolates of each ERP pattern were also emm-typea, a sequence typing method that correlates with serological M-typing.
Results. 28% of the group 1 children were found to carry S. pyogenes for more than two months. This carriage rate is similar to that previously detected in Dunedin and Waikato schoolchildren, but is higher than that generally reported in other countries. Although the predominant S. pyogenes types detected 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 Dunedin children.
Conclusion. The high pharyngeal carriage rates of S. pyogenes in Dunedin schoolchildren, without the concomitant increased occurrence of post-streptococcal sequelae observed in North Island populations may, in part, be due to a relatively lower occurrence of the M-types most commonly implicated in these diseases.
NZ Med J 2000; 113: 496-9
Streptococcus pyogenes (Lancefield group A streptococcus) is the most common cause of bacterial pharyngitis in children aged five to fifteen. Many children display mild or no clinical symptoms of infection and asymptomatic carrier rates of 5 to 15% are commonly reported.1 The risk for development in school-aged children of rheumatic fever or glomerulonephritis, following untreated S. pyogenes pharyngitis, is ever present, and New Zealand continues to have a higher per capita incidence of rheumatic fever than most developed countries, with Maori and Pacific Island populations disproportionately represented.2"4 South Island rates of rheumatic fever, however, are significandy lower than those reported in the North Island.2 Of the more than 100 M-protein serotypes (M-types) of S. pyogenes currendy recognized, relatively few have historically been directly incriminated in the development...