Scarlet fever, also called scarlatina, is an infection with Streptococcus pyogenes bacteria. The seriously pathogenic subgroup will belong to serogroup A, and show β-hemolysis when cultured on blood agar.
Its chief complaint is often sore throat with tonsillitis and pharyngitis. An erythematous rash, caused by a bacterial toxin is common, giving the disease its name. Characteristically, the reddened areas will desquamate (i.e., peel) during recovery, perhaps 6 weeks aftr onset.
It should be suspected in situations with sudden onset of a sore throat with rash. There are characteristic colorations of the tongue, starting as white and becoming purplish. Throat culture remains the definitive test, Rapid antigen tests are available and often can be used to justify starting antibiotic therapy, but negative tests should be confirmed by culture. The leukocyte count may elevate to 12,000-16,000 cells per mm3. Later in the disease, the eosinophil percentage may rise as high as 20%.
Toxins and other biologically active substances are some of the major concerns for complications such as toxic shock syndrome, which involve a form of the bacterium that attacks the kidneys. Approximately 3% of untreated and 0.3% of untreated cases may continue to rheumatic fever, which can do permanent heart damage.