According to the Duke criteria, which finding is a major criterion for infective endocarditis?

• A. Two separate blood cultures positive
• B. Osler's nodes
• C. Roth spots
• D. Fever >38°C

Answer: (A)

In the Duke criteria, major criteria are the strongest evidence of endocardial infection and include positive blood cultures with organisms typical of endocarditis drawn from two separate samples, or clear imaging showing endocardial involvement such as vegetations or new valvular regurgitation. Having two separate blood cultures that are positive demonstrates sustained bacteremia from infection of the heart valves, which directly supports infectious endocarditis and thus fits a major criterion. Osler nodes and Roth spots are immune-related phenomena and fever above 38°C is a nonspecific systemic sign; these are considered minor criteria. So, the finding of two separate positive blood cultures is the best major criterion among the options.