Infective endocarditis is an infection of the heart valves or endocardium caused by bacterial, viral, or fungal microorganisms. Blood cultures are used to detect the bacteria causing infective endocarditis, and echocardiography is performed to find the damaged heart valves. In blood culture-negative endocarditis, no endocarditis-causing organisms can be found in blood cultures, and blood cultures using usual laboratory methods remain sterile after inoculation of at least three independent blood samples.


Case presentation
A 24-year-old male with a history of polysubstance abuse presented with complaints of fever, cough, and shortness of breath. He had a past history of pulmonary tuberculosis 4 years ago, for which he was treated with antitubercular therapy. High-resolution computed tomography of the chest revealed multiple cavitary lesions and consolidative areas in the bilateral lungs. Based on these findings, a provisional diagnosis of reactivation of pulmonary tuberculosis was considered, and antitubercular therapy was started. Due to his deteriorating condition, he was readmitted and evaluated. Bronchoalveolar lavage was done and sent for culture and sensitivity testing, which showed the presence of Staphylococcus aureus, and treatment was started accordingly. Despite continuing intravenous antibiotics for 5 days, the patient was not improving. Three sets of samples were withdrawn for blood culture and sensitivity testing, which came out to be negative. Transthoracic echocardiography was done, which revealed vegetation in the tricuspid valve. The patient was diagnosed with culture-negative tricuspid valve endocarditis based on the clinical criteria.


Discussion
Blood culture-negative endocarditis is difficult to diagnose and presents challenges. When faced with a diagnosis like culture-negative endocarditis in the context of a condition that can appear very similar, like tuberculosis, a broad differential diagnostic approach is important.


Conclusion
Intravenous drug use is the main cause of right-sided valvular infective endocarditis. Endocarditis should be considered in intravenous drug users even in the absence of positive blood cultures. An appropriate antibiotic regimen and long-term follow-up with a multidisciplinary team are necessary for a good outcome.