Chapter 285

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.

### Epidemiology

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.

### Pathophysiology

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 ...

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