Side effects of srep throat?

Rheumatic Fever: The reason why we test and treat strep throat is because a certain percentage can lead to rheumatic fever, an inflammatory disease that can affect the skin, brain, joints, and most importantly the heart. This dammage to the heart leads to congestive heart failure and early death. It was a major problem before the widespread use of penicillin in 60's.

Rheumatic fever: Untreated pharyngeal infection with streptococcus pyogenes may result in acute rheumatic fever. On rare occasions it may disseminate and produce severe infections elsewhere in the body, but this is highly unlikely.