A 35-year-old woman is undergoing aortic valve replacement for chronic aortic valvulitis from rheumatic fever. She was doing well until about a week prior to admission, when she developed worsening dyspnea. A chest radiograph showed pulmonary edema and mild cardiomegaly with a prominent left heart border. An echocardiogram revealed high grade aortic stenosis.

She has an uncomplicated surgical procedure, in which a porcine bioprosthesis is impanted. She does well for three weeks, but then develops a low-grade fever that persists for several days. Blood cultures are performed, and 2 of 5 cultures grow an organism.

Question 1.1 - Why was a bioprosthesis used?

She is of reproductive age with menstruation, and may still want to become pregnant. A mechanical prosthesis would require anticoagulation.

Question 1.2 - What are complications of prosthetic valves?

Infection and thrombosis (or bleeding with anticoagulation) are the major events. Complications of valve placement and surgery are less common. Failure of mechanical prostheses is now very rare. Bioprostheses wear out and calcify and must be replaced after 5 to 10 years.

Question 1.3 - What are the likely microbiologic agents to cause this infection?

The top organisms with nosocomial infections of valve prostheses, within 2 months of surgery, are: S. epidermidis (35%), S. aureus (13%), enterococcus (13%), streptococci (10%), and various fungi (6%).

Question 1.4 - How does the setting for this disease contribute to the microbiologic risk (nosocomial infection)?

Any time there are abnormal surfaces and diminished health status (post-operative state, nutritional issues, underlying diseases) then the risk for endocarditis increases.

Question 1.5 - What antibiotic regimen is indicated?

Methicillin or nafcillin, if sensitive. If resistant, then vancomycin.