Innocuous to insidious: an unpredictable diagnosis of Streptococcus sanguinis infective endocarditis in a young adult.

Streptococcus sanguinis is a commensal oral flora and an opportunistic pathogen prevalently implicated in native valve infective endocarditis (IE). However, in developing nations, infective endocarditis is currently affecting young healthy adults. In this case report, we presented a case of a 26-year-old male with Streptococcus sanguinis endocarditis without obvious aetiology, which was initially diagnosed and treated for dengue fever. A full medical history, physical examination, procedures such as transoesophageal echocardiography and electrocardiogram, and laboratory tests of full blood count and blood cultures were obtained to diagnose infective endocarditis based on the modified Duke criteria. The patient underwent mitral valve replacement with antibiotic therapy and currently presents no further complications. This article underscores the significance of thorough clinical assessment on patients and the hidden, life-threatening complications of Streptococcus sanguinis infective endocarditis if left untreated.