**Core Concept**
The best site for collection of specimen for Neisseria meningitidis (N. meningitidis) infection is crucial for accurate diagnosis and treatment. N. meningitidis is a gram-negative bacterium that causes meningitis, a life-threatening infection of the meninges, the protective membranes surrounding the brain and spinal cord.

**Why the Correct Answer is Right**
The correct site for collecting a specimen for N. meningitidis is the cerebrospinal fluid (CSF) via lumbar puncture (LP). This is because N. meningitidis typically colonizes the nasopharynx but can invade the CSF, causing meningitis. The CSF is the most reliable specimen for detecting the bacteria, as it contains high concentrations of N. meningitidis during the early stages of infection. The CSF is collected through a sterile needle inserted into the lumbar region of the spine, allowing for direct access to the CSF.

**Why Each Wrong Option is Incorrect**
**Option A:** Blood cultures may be positive in some cases, but they are not the best site for collection due to the lower sensitivity and specificity for N. meningitidis.
**Option B:** Nasopharyngeal swabs can detect N. meningitidis colonization, but they are not the best site for collection in cases of suspected meningitis, as the bacteria may not be present in the CSF.
**Option C:** Urine cultures are not typically used for diagnosing N. meningitidis infections.

**Clinical Pearl / High-Yield Fact**
In cases of suspected bacterial meningitis, it is essential to collect a CSF specimen via LP as soon as possible, as delays in treatment can lead to increased morbidity and mortality.

**Correct Answer:** C. Cerebrospinal fluid (CSF) via lumbar puncture (LP).