Scarlet Fever: Causes and symptoms

Scarlet fever is caused by Group A streptococcal bacteria (S. pyogenes). Group A streptococci can be highly toxic microbes that can cause strep throat, wound or skin infections, pneumonia, and serious kidney infections, as well as scarlet fever. The Group A streptococci are ß-hemolytic bacteria, which means that the bacteria have the ability to lyse or break red blood cells. The strain of streptococcus that causes scarlet fever is slightly different from the strain that causes most strep throats. The scarlet fever strain of bacteria produces a toxin, called an erythrogenic toxin. This toxin is what causes the skin to flush.

The main symptoms and signs of scarlet fever are fever, lethargy, sore throat, and a bumpy rash that blanches under pressure. The rash appears first on the upper chest and spreads to the neck, abdomen, legs, arms, and in folds of skin such as under the arm or groin. In scarlet fever, the skin around the mouth tends to be pale, while the cheeks are flushed. The patient usually has a "strawberry tongue," in which inflamed bumps on the tongue rise above a bright red coating. Finally, dark red lines (called Pastia's lines) may appear in the creases of skin folds.

— Sally J. Jacobs, EdD