Which of the following is a risk factor for infective endocarditis?

The use of intravenous (IV) drugs is a significant risk factor for developing infective endocarditis. This is primarily due to the manner in which IV drugs are commonly administered. When needles or syringes that are not sterile are used, or when injections are made into veins that are not clean, bacteria can be introduced directly into the bloodstream. This provides a pathway for these microorganisms to travel to the heart, where they can adhere to damaged heart valves or endocardial surfaces, leading to infection and potentially serious complications.

Recent surgical procedures, while they can sometimes be associated with a risk of infective endocarditis, particularly if the procedure involves the heart or blood vessels, do not pose as high a risk as IV drug use in general cases. The use of antibiotics might actually reduce the risk of certain infections, including endocarditis, by treating bacterial infections beforehand. Lastly, while a family history of heart disease may suggest congenital or structural heart defects, which can be risk factors for endocarditis in some contexts, it is not as direct a risk factor as IV drug use. Therefore, among the choices given, IV drug use stands out as a clear and well-documented risk factor for infective endocarditis.