Group A beta-hemolytic streptococcus (GABHS) is most common (see Streptococcal Infections), but Staphylococcus aureus, Streptococcus pneumoniae, Mycoplasma pneumoniae, and Chlamydia pneumoniae are sometimes involved. Rare causes include pertussis, Fusobacterium, diphtheria, syphilis, and gonorrhea.