**Core Concept:** Infective endocarditis is an infection of the inner lining (endocardium) of the heart, typically involving the heart valves. It is caused by bacteria or other microorganisms, and can lead to complications such as heart valve damage and systemic embolization. The correct answer refers to the rare cases where this infection is seen in a specific group or location.

**Why the Correct Answer is Right:** The correct answer (D) is right because infective endocarditis is rarely seen in infants due to the immaturity of their cardiovascular system. Infants have thinner heart valves and a higher risk of developing valvular defects, which makes them more susceptible to this infection.

**Why Each Wrong Option is Incorrect:**

A. This option is incorrect because infective endocarditis can occur in children and adolescents, although it is more common in adults.

B. This option is incorrect because infective endocarditis can affect people of all ages, including adults and the elderly.

C. This option is incorrect because infective endocarditis can occur in individuals with pre-existing heart conditions or defects, regardless of age.

**Clinical Pearl / High-Yield Fact:** Infective endocarditis in infants warrants a high index of suspicion, as it can present with non-specific symptoms like fever, irritability, and poor feeding. Early diagnosis and treatment are crucial to prevent complications like heart failure, stroke, and cerebral abscesses.

**Correct Answer:** .