STREPTOCOCCUS PYOGENES (group A streptococcus) is one of the most common and ubiquitous of human pathogens. It causes a wide array of infections, the most frequent of which are acute pharyngitis ("strep throat") and impetigo (pyoderma). Other manifestations of infection with group A streptococcus include sinusitis, otitis, peritonsillar and retropharyngeal abscess, pneumonia, scarlet fever, erysipelas, cellulitis, lymphangitis, puerperal sepsis, vaginitis, myositis, gangrene, and perianal cellulitis. The organism has, moreover, long been the focus of intense clinical and investigative interest because of its association with two nonsuppurative sequelae: acute rheumatic fever and acute glomerulonephritis. Infections caused by group A streptococci were . . .