Potentially virulent strains and high colony counts of group A beta-haemolytic streptococci in pharyngitis patients having a delayed recovery or a complication.

T serotyping and M and exotoxin genotyping were performed on strains from 367 streptococcal pharyngitis patients in Dutch general practice. Potentially virulent strains of group A beta-haemolytic streptococci, such as T1M1 and T3M3 subtypes and strains expressing speA and speC, and a high number of colony counts did not occur more frequently in the 166 (45%) more seriously ill patients, defined as those who showed a delayed recovery or a complication.