Scarlet fever is an upper respiratory tract infection associated with a characteristic rash, which is caused by an infection with pyrogenic exotoxin (erythrogenic toxin)–producing Group A Streptococcus in individuals who do not have antitoxin antibodies. It is now encountered less commonly and is less virulent than in the past, but the incidence is cyclic, depending on the prevalence of toxin-producing strains and the immune status of the population. The modes of transmission, age distribution, and other epidemiologic features are otherwise similar to those for GAS pharyngitis.
The rash appears within 24–48 hr after onset of symptoms, although it may appear with the 1st signs of illness . It often begins around the neck and spreads over the trunk and extremities. It is a diffuse, finely papular, erythematous eruption producing a bright red discoloration of the skin, which blanches on pressure. It is often more intense along the creases of the elbows, axillae, and groin. The skin has a goose-pimple appearance and feels rough. The face is usually spared, although the cheeks may be erythematous with pallor around the mouth. After 3–4 days, the rash begins to fade and is followed by desquamation, 1st on the face, progressing downward, and often resembling that seen subsequent to a mild sunburn. Occasionally, sheetlike desquamation may occur around the free margins of the fingernails, the palms, and the soles.
Examination of the pharynx of a patient with scarlet fever reveals essentially the same findings as with GAS pharyngitis.
In addition, the tongue is usually coated and the papillae are swollen. After desquamation, the reddened papillae are prominent, giving the tongue a strawberry appearance.
Typical scarlet fever is not difficult to diagnose; however, the milder form with equivocal pharyngeal findings can be confused with viral exanthems, Kawasaki disease, and drug eruptions. Staphylococcal infections are occasionally associated with a scarlatiniform rash. A history of recent exposure to a GAS infection is helpful. Identification of GAS in the pharynx confirms the diagnosis, if uncertain.