An outbreak of
scarlet fever involving 12 children occurred at a hospital
day care centre from February to March 1996. Twenty-five throat isolates of Streptococcus pyogenes (GAS, group A streptococcus) available from 24 children, including 10 children with
scarlet fever and 14 asymptomatic carriers, and one asymptomatic staff member were studied for the presence of genes encoding
streptococcal pyrogenic exotoxin types A (speA), B (speB), and C (speC) and for
protease activity. Antimicrobial susceptibilities using the E-test, cluster analysis by cellular
fatty acid composition and random amplified polymorphic
DNA (RAPD) patterns by means of arbitrarily-primed polymerase chain reaction (APPCR) of the isolates were performed to investigate the outbreak. Only one isolate from an asymptomatic child possessed the speA gene. All isolates possessed the speB gene and 24 (96%) isolates were positive for the speC gene. There was no difference in
protease activity between isolates from children with
scarlet fever and from asymptomatic carriers. Thirteen isolates (10 recovered from children with
scarlet fever, two from asymptomatic children, and one from the staff member) were considered to be the same strain according to the identical antimicrobial susceptibility profile and RAPD patterns and were also considered to be similar by cluster analysis of
fatty acid composition. These findings suggest that the outbreak was caused by a unique clone of GAS. We conclude that RAPD typing and cluster analysis by cellular
fatty acids composition both provide a powerful tool for epidemiological investigation of GAS
infections.