**Core Concept**
The question is testing the knowledge of appropriate specimen collection for diagnosing chlamydial infection in a neonate. Chlamydia trachomatis is a sexually transmitted bacterium that can be transmitted from mother to baby during birth, leading to neonatal chlamydial infection. Early diagnosis and treatment are crucial to prevent long-term complications.

**Why the Correct Answer is Right**
The correct answer is **Cervical swab**. A cervical swab is the preferred specimen collection method for diagnosing chlamydial infection in neonates. This is because the bacteria are more likely to be present in the cervix and vagina of the infected mother. The swab is taken from the baby's eyes, usually within the first 2 weeks of life, to detect the presence of C. trachomatis. The specimen is then sent for culture or PCR analysis to confirm the diagnosis.

**Why Each Wrong Option is Incorrect**
**Option A:** **Blood sample** is not the preferred method for diagnosing chlamydial infection in neonates. Although blood tests can detect antibodies against C. trachomatis, they are not reliable for diagnosing active infection in newborns.

**Option B:** **Urine sample** is not the primary method for diagnosing chlamydial infection in neonates. While urine tests can detect C. trachomatis, they are not as sensitive as cervical swab or PCR analysis.

**Option D:** **Nasopharyngeal swab** is not the preferred method for diagnosing chlamydial infection in neonates. Although nasopharyngeal swabs can detect C. trachomatis, they are not as sensitive as cervical swab or PCR analysis.

**Clinical Pearl / High-Yield Fact**
It's essential to note that a single dose of azithromycin is the recommended treatment for neonatal chlamydial infection. Early treatment is crucial to prevent long-term complications, such as conjunctivitis and pneumonia.

**Correct Answer:** C. Cervical swab