Etiology Occurs after an episode of group A streptococcal (Streptococcus pyogenes bacteria) pharyngitis Incidence: peak ages are between 5 and 15 yrs Streptococcus pyogenes a bacteria. A pus specimen viewed using Pappenheim's stain◼ Occurs after an episode of group A streptococcal (Streptococcus pyogenes bacteria) pharyngitis ◼ Incidence: peak ages are between 5 and 15 yrs Etiology Streptococcus pyogenes bacteria. A pus specimen, viewed using Pappenheim's stain