In a neonate with “classic” symptoms of congenital cytomegalovirus (CMV) infection, which one of the following tests would be most useful in establishing a diagnosis?
**Core Concept**
Congenital cytomegalovirus (CMV) infection is a leading cause of birth defects and developmental disabilities in neonates. Diagnosis relies on identifying viral DNA or antigens in neonatal samples.
**Why the Correct Answer is Right**
The detection of CMV DNA in urine or saliva is the most sensitive and specific method for diagnosing congenital CMV infection. This is because CMV is predominantly excreted in the urine of infected neonates. Polymerase Chain Reaction (PCR) is a molecular technique that amplifies viral DNA, allowing for its detection in a sample. This method is particularly useful in the first few weeks of life when the virus is most active.
**Why Each Wrong Option is Incorrect**
* **Option A:** Blood cultures are not a reliable method for diagnosing congenital CMV infection as the virus is not typically isolated from blood.
* **Option B:** CMV IgM antibodies in maternal serum can indicate recent infection, but their presence in neonatal serum is not a definitive diagnosis of congenital CMV infection.
* **Option D:** Serology (measuring CMV antibodies) is not useful in neonates as they may have passively acquired antibodies from their mother.
**Clinical Pearl / High-Yield Fact**
In neonates with suspected congenital CMV infection, urine PCR is the preferred diagnostic test due to its high sensitivity and specificity.
**Correct Answer:** C.