The disease occurs as a sequela to streptococcal pharyngitis, and the latent period between the period of infection and the onset of disease varies from 2 to 6 weeks or longer. ARF is almost exclusively associated with the group A strains that cause pharyngitis, and rarely, if ever, follows infections that cause impetigo or kidney disease.

The available evidence suggests that the abnormal immune response of the host to streptococcal antigens cross-reactive with target mammalian antigens, at both cellular and humoral level, is responsible for the pathologic damage. These cross-reactive antigens include the hyaluronic capsule of the streptococcus and a number of streptococcal antigens, including M proteins that share antigenic determinants with cardiac tropomyosin and myosin. Similar molecular mimicry appears to play a role in the pathology found in the kidney, central nervous system, and skin.

A genetic basis for the disease has been suggested for more than 100 years, and family studies indicate that gene inheritance is either autosomal recessive or dominant with limited penetrance.

Both the prevalence and severity of rheumatic fever have declined dramatically during the last six decades in the United States and other developed countries; however, a resurgence in new and recurrent cases deserves renewed attention. Changes in living conditions, nutrition, and virulence of the organism, in addition to antibiotic therapy for streptococcal pharyngitis, have all been suggested as reasons for the decreased incidence.

The overall incidence of rheumatic fever in the United States is currently estimated to be less than 1 in 100,000 children of school age/year, but groups with poor standards of living have a much higher incidence. In some developing nations, the incidence of rheumatic fever remains high: 60 in 100,000 children (aged between 5 and 14 years)/year or more.

Rheumatic heart disease, a chronic sequela of rheumatic fever, is the most common cause of heart disease in individuals younger than 40 years in these countries. Rheumatic fever therefore represents a significant worldwide health problem.

Antecedent streptococcal pharyngitis most commonly occurs 2 to 3 weeks before the onset of the symptoms of rheumatic fever. It may be mild, however, and a history of fever and sore throat cannot be elicited in all patients.

Fever, which has no specific pattern, is almost always present at the onset of an acute attack and fades away in days to weeks without anti-inflammatory treatment. Fever resolves promptly with salicylate therapy.

Arthritis with fever is the most common manifestation of ARF, occurring in 50% to 75% of cases. It usually involves the large peripheral joints, especially the knees and ankles, but any joint may be affected. Arthritis, which occurs within 5 weeks of the streptococcal infection (when antistreptococcal antibody titers are usually high), subsides without treatment in a few weeks and very rarely causes joint deformity. Carditis occurs less frequently in cases with severe arthritis.

Arthralgia without objective evidence of joint inflammation may precede the development of synovitis. Severe arthralgia, especially if migratory, is an important diagnostic feature.

Carditis is the most important manifestation of ARF because it frequently leads to chronic valvular damage. In rare cases, it is a cause of death from cardiac failure or arrhythmias associated with myocarditis during an acute episode. Carditis occurs in 40% to 50% of attacks of ARF in some series, but this incidence seems to be decreasing.