From the Guidelines
Diagnostic tests for meningococcal meningitis should primarily involve cerebrospinal fluid (CSF) analysis obtained through lumbar puncture, with PCR of CSF being a crucial rapid diagnostic test, as it offers high sensitivity and specificity with results available within hours 1. The CSF typically shows elevated white blood cell count (predominantly neutrophils), increased protein, and decreased glucose.
- Gram stain of CSF may reveal gram-negative diplococci, which is highly suggestive of Neisseria meningitidis infection.
- CSF culture remains the gold standard for definitive diagnosis, though results take 24-72 hours.
- Blood cultures should also be obtained as bacteremia is common.
- Additional tests include latex agglutination for bacterial antigens in CSF and serum, though these are less sensitive than culture or PCR.
- CT scan of the head may be performed before lumbar puncture if there are concerns about increased intracranial pressure, as recommended by guidelines for patients with suspected bacterial meningitis who should undergo CT prior to lumbar puncture 1. It's essential to note that antibiotics should not be delayed for diagnostic testing if meningococcal meningitis is suspected, as early treatment significantly improves outcomes, and guidelines recommend sending blood for culture, pneumococcal and meningococcal PCR, and other tests as soon as possible 1. Throat swabs and skin lesion samples may also be cultured if present, particularly the characteristic petechial or purpuric rash seen in meningococcal disease. The use of latex agglutination tests is not recommended as a routine diagnostic method due to their limited value and potential for false-positive results 1. PCR techniques appear to be promising for the etiologic diagnosis of bacterial meningitis, with high sensitivity and specificity, and may be useful for excluding the diagnosis of bacterial meningitis 1.
From the Research
Diagnostic Tests for Meningococcal Meningitis
The diagnosis of meningococcal meningitis can be confirmed through various tests, including:
- Isolation of Neisseria meningitidis from blood or cerebrospinal fluid (CSF) 2
- Detection of gram-negative diplococci in CSF 2
- Polymerase chain reaction (PCR) to detect meningococcal DNA in CSF 2, 3, 4, 5, 6
- Latex agglutination, although its sensitivity is highly variable 3
- Gram stain and culture of CSF, which may be negative if antibiotic treatment has commenced prior to lumbar puncture 3, 5, 6
- PCR-Mass spectrometry for the simultaneous detection of multiple meningitis-causing agents, including Neisseria meningitidis 4
Advantages of PCR in Diagnosis
PCR has been shown to be a rapid and sensitive test for the diagnosis of meningococcal meningitis, with a sensitivity of 91% and specificity of 91% 2. It is particularly useful when other methods are negative or delayed, such as when antibiotic treatment has been started before lumbar puncture 3, 6. PCR can also determine the serogroup of Neisseria meningitidis, which is important for epidemiological purposes and vaccine development 6.
Comparison of Diagnostic Tests
Studies have compared the sensitivity and specificity of different diagnostic tests for meningococcal meningitis. For example, one study found that PCR had a higher sensitivity (89%) than bacteriological culture (37%) 6. Another study found that PCR-Mass spectrometry had an overall agreement rate of 85.7% with real-time PCR 4. These findings suggest that PCR and PCR-Mass spectrometry are valuable tools for the diagnosis of meningococcal meningitis, particularly when other tests are negative or delayed.