69 Presumptive diagnosis of MRSA bacteremia delays closure of symptomatic patent foramen ovale and leads to complications of unnecessary antimicrobial therapy

A 70-year old male with a history significant for a remote ischemic stroke of unclear etiology presented to hospital with altered level of consciousness (LOC). One of two peripheral blood cultures showed polymicrobial growth including methicillin resistant Staphylococcus aureus (MRSA) and two presumed contaminants; complete work-up, including head imaging and transthoracic echocardiography, was otherwise unrevealing. He was treated for MRSA bacteremia with normalization of his mentation. Recurrent episodes of altered LOC with transient hypoxia and witnessed seizures resulted in multiple hospital re-admissions, with subsequent workup revealing radiographic evidence of new subacute bilateral intracranial infarcts, and echocardiographic evidence of a patent foramen ovale (PFO), large right-to-left shunt, interatrial septal aneurysm and Chiari network with an attached mobile filamentous mass. Given initial single culture positivity for MRSA despite no clinical or radiographic evidence of MRSA bacteremia or endocarditis, surgical closure was deferred, and a prolonged course of antibiotics was pursued. His hospital stay was subsequently prolonged by antimicrobial-related cytopenias, line-related fungemia, and significant deconditioning, further delaying time to surgical intervention. He eventually underwent PFO closure in the outpatient setting, and has not had altered LOC episodes since. This case illustrates important concepts in overdiagnosis and overtreatment, demonstrating how clinical decision-making may be misguided by a presumptive diagnosis, with unintended negative outcomes and delays in accessing necessary investigations and treatments.