What organism most likely caused the rheumatic mitral valve disease in a 39‑year‑old man with orthopnea, a holosystolic murmur, and a history of streptococcal pharyngitis?

Rheumatic Mitral Valve Disease: Causative Organism

The organism that caused this patient's rheumatic mitral valve disease is group A beta-hemolytic streptococcus (Streptococcus pyogenes). 1

Clinical Reasoning

This 39-year-old man presents with classic features of chronic rheumatic heart disease:

• Holosystolic murmur indicates mitral regurgitation from valvular damage 2
• Orthopnea (shortness of breath when lying flat) suggests heart failure from significant mitral valve dysfunction 2
• History of childhood sore throat infections points to prior group A streptococcal pharyngitis 1

Pathophysiological Mechanism

Group A beta-hemolytic streptococcus causes rheumatic fever through an autoimmune mechanism triggered by pharyngeal infection. 1

The disease progression follows this pathway:

• Initial infection: Group A streptococcus pharyngitis occurs, typically in childhood 3, 4
• Autoimmune response: The M-protein serotypes of the organism share structural similarities with human cardiac tissues, triggering cross-reactive antibodies 1, 3
• Acute rheumatic fever: Develops 14-21 days after the pharyngitis in genetically susceptible individuals 3
• Valvular damage: Repeated episodes of acute rheumatic fever cause progressive valvular injury through immune-inflammatory mechanisms 5, 4
• Chronic rheumatic heart disease: Results from commissural fusion, scarring, and calcification of valve cusps, particularly affecting the mitral valve 1, 3

Key Diagnostic Features

The mitral valve is preferentially affected in rheumatic heart disease, with mitral regurgitation being the most common manifestation in the acute and chronic phases. 3, 6

• Rheumatic mitral stenosis develops from commissural fusion with scarring and calcification 1, 3
• When aortic valve involvement occurs, it is invariably accompanied by mitral valve disease 3
• 60-65% of patients who recover from acute rheumatic fever develop chronic valvular heart disease 3

Clinical Pitfall to Avoid

Do not confuse this with infective endocarditis. While streptococcal species (particularly Streptococcus mitis and Streptococcus bovis) can cause infective endocarditis 1, the clinical presentation here—with childhood pharyngitis history, chronic progressive course, and orthopnea—indicates rheumatic heart disease from prior group A streptococcal infection rather than acute endocarditis. 1

Prevention Implications

Prompt recognition and treatment of group A streptococcal pharyngitis with penicillin within 9 days can prevent acute rheumatic fever. 1, 2

• Rapid antigen detection tests have >95% specificity for identifying group A streptococcus 1
• Patients with documented rheumatic heart disease require continuous antimicrobial prophylaxis (secondary prevention) for at least 10 years or until age 40, whichever is longer 1, 3