What kind of illnesses are caused by group a streptococcal infection?

Several: Untreated streptococcal infection can cause permanent heart damage, kidney problems , arthritis, skin infections and more. That is why you should see your doctor if you have a sore throat to determine if you need antibiotics to prevent these complications.

Classical: This could include secondary complications of rheumatic fever, kidney failure from glomerulonephritis, and several other problems, including acute bacterial endocarditis. Hope my internal medicine colleagues also give you answers, as mine may cover only part of the complications.