BACKGROUND: Several outbreaks of scarlet fever caused by Streptococcus pyogenes 
were recently reported. Scarlet fever is historically considered a 
toxin-mediated disease, dependent on the production of the exotoxins SpeA and 
SpeC, but a strict association between scarlet fever and these exotoxins is not 
always detected. The aims of this study were to characterize the scarlet fever 
bacterial isolates recovered from patients in a Lisbon hospital and to identify 
any distinctive characteristics of such isolates.
METHODS: We characterized a collection of 303 pharyngeal S. pyogenes collected 
between 2002 and 2008. One-hundred and one were isolated from scarlet fever 
patients and 202 were associated to a diagnosis of tonsillo-pharyngitis. 
Isolates were characterized by T and emm typing, pulsed field gel 
electrophoresis profiling and superantigen gene profiling.
RESULTS: The diversity of the scarlet fever isolates was lower than that of the 
pharyngitis isolates. Specific lineages of emm87, emm4 and emm3 were 
overrepresented in scarlet fever isolates but only 1 pulsed field gel 
electrophoresis major lineage was significantly associated with scarlet fever. 
Multivariate analysis indicated associations of ssa, speA and speC with scarlet 
fever.
CONCLUSIONS: In nonoutbreak conditions, scarlet fever is caused by a number of 
distinct genetic lineages. The lower diversity of these isolates and the 
association with specific exotoxin genes indicates that some lineages are more 
prone to cause this presentation than others even in nonoutbreak conditions.