++
Streptococcus pyogenes infections
were likely responsible for the apparent scarlet fever epidemic described
by Hippocrates in the 5th century BC. The history of S pyogenes has
been the subject of a comprehensive review.1 The
first modern description of streptococcal infection was the demonstration
of the organism in patients with erysipelas and wound infection
in 1874. The organism was designated Streptococcus pyogenes by
Rosenbach in the late 19th century. In the early 1930s, Rebecca
Lancefield’s classification of the β-hemolytic
strains into characteristic distinct serogroups led to the recognition
that serogroup A isolates (S pyogenes) were the
streptococcal strains most commonly responsible for pharyngitis
and impetigo/pyoderma. Streptococcus pyogenes is
one of the most important infectious agents encountered in clinical
practice causing infections of the upper respiratory tract and of
the skin, that causes a variety of severe systemic infections, including
toxic shock syndrome and life-threatening skin and soft tissue infections.
Infection with this pathogen is also causally linked to two serious
nonsuppurative complications, acute rheumatic fever and acute glomerulonephritis.
++
Streptococcus pyogenes is highly communicable.
Respiratory droplet spread is the major route for transmission of
strains associated with upper respiratory tract infection, although
skin-to-skin spread is known to occur with strains associated with
pyoderma. Foodborne outbreaks are not rare and often are associated
with egg-containing foods. Although uncommon, nursery outbreaks of
group A streptococcal infections have been reported. The incidence
of pharyngeal infection with group A streptococci is highest in
children ages 5 to 15 years. Indeed, group A streptococcal pharyngitis
has been described as an “occupational disease” of
school-aged children. Streptococcus pyogenes also
has the potential to produce outbreaks of disease in younger children in
group daycare. In temperate zones, pharyngeal infection is most
common during late autumn, winter, and early spring. Group A streptococcal
skin infections occur most frequently during the summer in temperate
climates but can occur year-round in warmer climates.
++
Streptococci are gram positive cocci
that tend to grow as pairs and chains. When cultured on sheep or
horse blood agar plates, a characteristic zone of complete hemolysis
(β-hemolysis) is observed. Streptococcus
pyogenes (group A streptococci) may be identified either
by serologic means or latex agglutination techniques. Additional
typing of group A streptococci for epidemiologic purposes is based
on variation in the M and T proteins and emm genes
(see below). The somatic cellular constituents as well as the extracellular
enzymes and toxins responsible of S pyogenes are
responsible for many of pathogenic effects observed in vivo. These
also are summarized in eTable 285.1.2,3 A
complete and current listing of recognized types of group A streptococci
is available at the Centers for Disease Control (CDC) Web site (http://www.cdc.gov/ncidod/biotech/strep/strepindex.htm).
The major virulence factor of the organism is the M protein. This
protein is anchored to the cell membrane and transverses and penetrates
the cell wall. Functionally, the M proteins inhibit phagocytosis,
which ...