First Described Case of Infective Endocarditis Involving the Pulmonary Valve Caused by Moraxella catarrhalis

Moraxella catarrhalis, once considered a component of the normal human flora of the upper respiratory tract, is now recognized as a true pathogen and, rarely, a cause of infective endocarditis (IE).

We describe a rare case of a 36-year-old woman who presented with respiratory symptoms and was initially misdiagnosed with pneumonia and M. catarrhalis bacteremia. No vegetations were seen on transesophageal echocardiogram (TOE) imaging. However, further investigation with cardiac computed tomography (CT) revealed prosthetic pulmonary valve IE caused by M. catarrhalis, which also resulted in pulmonary abscesses.

This case highlights the importance of considering M. catarrhalis as a true pathogen in invasive disease, including prosthetic pulmonary valve IE. It also demonstrates the limitations of negative TOE findings in the evaluation of right-sided IE, particularly when prosthetic valves are involved. Cardiac CT is crucial when TOE results are negative but clinical suspicion for prosthetic right-sided IE remains high, as it aids in diagnosing both the infection and its perivalvular or periprosthetic complications.