Scarlet Fever

Scarlet fever is the toxin-mediated form of infection with Group A Streptococcus (GAS), also called Streptococcus pyogenes. The organism commonly causes pharyngitis; when its toxin produces a diffuse exanthem, the illness is recognised as scarlet fever. The rash is therefore not a separate infection—it is a clue that the GAS illness has a toxin-associated skin manifestation. The classic presentation is a febrile child with a sore throat and a fine, diffuse rash that feels rough, almost like sandpaper. Clinical features supporting the diagnosis include a temperature of at least 38.3°C, circumoral pallor, and a rash that begins around the neck and spreads over the trunk. The palms and soles are often spared. The face may look flushed while the area around the mouth remains pale. The tongue often changes over the course of the illness. It may first have a white coating with prominent papillae and later become bright red—the familiar “strawberry tongue.” Linear petechiae in skin folds, known as Pastia lines, can provide additional support. No single skin finding replaces assessment for GAS, but the combination of pharyngitis, fever,...