This disease is a rare after-effect of the bacterial throat infection commonly known as "strep throat" (streptococcal pharyngitis). It occurs in patients that are not treated with antibiotics or are only partially treated with antibiotics for their throat infection. Strep throat is caused by the bacteria known as Group A streptococcus. Less than one half of one percent of the people who experience strep throat develop Acute Rheumatic Fever.
Acute Rheumatic Fever has become rare in the more developed countries, though incidents have increased in recent years, perhaps because of the development of more resistant strains of streptococcus.
This disease is most common in children between the ages of 5 and 15. It is uncommon in adults, and rare in children under the age of 4.