Final answer:
Rheumatic fever primarily affects children, particularly those who have had an episode of untreated or inadequately treated pharyngitis caused by Streptococcus pyogenes.
Step-by-step explanation:
Rheumatic fever primarily affects children, particularly those who have had an episode of untreated or inadequately treated pharyngitis caused by Streptococcus pyogenes. It occurs 2-3 weeks after the initial infection. Rheumatic fever is rare in the US due to early diagnosis and treatment with antibiotics, but it is still a major cause of mortality in children in parts of the world where diagnosis and treatment are not readily available.