Final answer:
Rheumatic fever usually develops 2-3 weeks after untreated or inadequately treated pharyngitis caused by specific strains of S. pyogenes. It primarily affects children and has become rare in the US due to early diagnosis and treatment with antibiotics.
Step-by-step explanation:
Rheumatic fever typically develops a minimum of 2-3 weeks after an episode of untreated or inadequately treated pharyngitis caused by specific rheumatogenic strains of S. pyogenes.
It occurs primarily in children. However, early diagnosis and treatment of streptococcal pharyngitis with antibiotics have significantly reduced the incidence of rheumatic fever in the US.