Differential Diagnosis for Prosthetic Valve Endocarditis

The patient's presentation with fever, rigors, weight loss, and small vegetation on the prosthetic mitral valve a month after surgery suggests prosthetic valve endocarditis. The differential diagnosis can be categorized as follows:

• Single most likely diagnosis

  • Staphylococcus epidermidis: This organism is a common cause of early prosthetic valve endocarditis, particularly within the first year after surgery. It is a skin commensal and can be introduced during the surgical procedure, making it a likely culprit in this scenario given the recent valve replacement.

• Other Likely diagnoses

  • Staphylococcus aureus: Known for its virulence and ability to cause endocarditis, S. aureus is another common cause of prosthetic valve infections, especially in the early postoperative period. Its presence can lead to severe disease.
  • Streptococcus viridans: Although more commonly associated with native valve endocarditis, Streptococcus viridans can also infect prosthetic valves, particularly if the patient has a history of dental procedures without adequate antibiotic prophylaxis.

• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)

  • Coxiella burnetii: The causative agent of Q fever, Coxiella burnetii is an uncommon but important cause of culture-negative endocarditis, including prosthetic valve endocarditis. It has a high mortality rate if not treated appropriately, making it crucial not to miss this diagnosis.

• Rare diagnoses

  • Other rare organisms such as fungi (e.g., Candida species), Enterococcus, Pseudomonas aeruginosa, and other gram-negative bacteria can also cause prosthetic valve endocarditis but are less common and typically associated with specific risk factors (e.g., healthcare-associated infections, intravenous drug use). These should be considered based on the patient's specific history and clinical context.