**Core Concept**
Early diagnosis of HIV infection in infants is crucial, as it allows for timely initiation of antiretroviral therapy (ART) to prevent mother-to-child transmission and long-term complications. The diagnosis of HIV in infants involves a combination of clinical evaluation, laboratory tests, and molecular assays.

**Why the Correct Answer is Right**
In infants, the diagnosis of HIV infection is challenging due to the presence of maternal antibodies, which can lead to false-positive results in serological tests. To overcome this limitation, molecular assays such as DNA polymerase chain reaction (PCR) are used to detect the presence of HIV DNA in the infant's blood. This method is highly sensitive and specific, allowing for early diagnosis of HIV infection.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because serological tests, such as enzyme-linked immunosorbent assay (ELISA), are not reliable for diagnosing HIV infection in infants due to the presence of maternal antibodies.
**Option B:** This option is incorrect because viral culture is not a reliable method for diagnosing HIV infection in infants, as it is time-consuming and has a low sensitivity.
**Option C:** This option is incorrect because p24 antigen test is not specific enough for diagnosing HIV infection in infants, as it can produce false-positive results due to the presence of maternal antibodies.

**Clinical Pearl / High-Yield Fact**
In infants, the diagnosis of HIV infection should be based on a combination of clinical evaluation, laboratory tests, and molecular assays, such as DNA PCR. This approach allows for early detection and treatment of HIV infection, which is essential for preventing long-term complications.

**Correct Answer:** A.