A 32-year-old man from rural India presents with a 5-day history of fever, malaise, and progressive dyspnea. On examination, he has a new diastolic murmur best heard at the left sternal border, splinter hemorrhages on the fingernails, and Osler nodes on the fingertips. Blood cultures grow *Streptococcus pyogenes*. Echocardiography shows vegetation on the aortic valve with severe aortic regurgitation. What is the most likely predisposing factor for this presentation?