Scarlet Fever

Excerpt

Scarlet fever is a syndrome characterized by a blanching, erythematous, maculopapular rash often described as "sandpaper-like," a "strawberry tongue," and exudative pharyngitis (see Image. Scarlet Fever). The causative organism, Streptococcus pyogenes (group A Streptococcus or "GAS"), is a gram-positive bacterium adapted to humans. This organism grows in pairs and chains and is responsible for a range of infections, including superficial, deep, and invasive conditions such as cellulitis, pharyngitis, erysipelas, and necrotizing fasciitis.

GAS produces streptococcal pyrogenic exotoxins (SPEs), which act as superantigens released during infection. These exotoxins are the primary cause of the erythematous rash associated with scarlet fever. GAS bacterial pharyngitis and scarlet fever most commonly affect school-age and adolescent children due to higher transmissibility in school settings. However, these infections can also occur in other age groups, particularly in crowded environments such as households and nursing homes.

Scarlet fever caused by GAS infections can occur at any age. Although it is most commonly associated with GAS pharyngitis, it may also develop with other GAS infections, whether invasive or noninvasive, such as erysipelas or necrotizing fasciitis. Historically, GAS serotypes have displayed cyclic epidemiological patterns. Notably, GAS is among the few bacteria that produce superantigen exotoxins, which are exceptionally potent activators of T cells. GAS superantigens, also referred to as erythrogenic or scarlet fever toxins, are responsible for the characteristic erythematous, sandpaper-like rash and strawberry tongue seen in scarlet fever. Superantigen genes, such as speA, speC, and ssa, enhance the fitness and virulence of GAS, contributing to the development of invasive disease.

Scarlet fever epidemics and invasive GAS infections were common in the 19th century. While the prevalence of scarlet fever declined in the 20th century, a resurgence of GAS infections occurred in the 1980s. In the past decade, more virulent epidemic strains of GAS have emerged, leading to an increase in both GAS infections and scarlet fever. Suppurative and non-suppurative complications can arise from GAS infections, including rheumatic heart disease (RHD) and poststreptococcal glomerulonephritis (PSGN). Prompt treatment of acute infections is essential to prevent these complications.