Introduction: Group A β-hemolytic streptococcus is a common infectious organism that causes illness in children and is highly contagious. In themselves, the diseases caused by streptococcus do not seem very serious (e.g., strep throat, otitis media, impetigo, or scarlet fever). The most common treatment for strep is a full course of antibiotic therapy: 10 days of penicillin (or, if allergic, erythromycin). With adequate therapy, generally no sequelae are seen. If the strep is not treated, or is only partially treated, the sequelae include serious systemic diseases, with potentially longterm effects. If the effect is manifested primarily in the heart (carditis), it is acute rheumatic fever. If the effect is manifested primarily in the kidneys, it is acute glomerulonephritis (see Figure 5-10. Genetic Transmission of Sickle Cell Anemia).