Diagnostic Considerations for Meningitis

Test Characteristics and Limitations

PCR testing, including multiplex platforms like BioFire, has a sensitivity of 87-100% and specificity of 98-100%, meaning some cases will be missed 1
Prior antimicrobial therapy can reduce the detection of bacterial pathogens in CSF, potentially leading to false-negative results 2

CSF culture remains the gold standard for diagnosing bacterial meningitis, with diagnostic rates of 70-85% in cases where antibiotics have not been given prior to lumbar puncture 3
When BioFire is negative but clinical suspicion remains high, additional testing should be considered, including conventional CSF culture, pathogen-specific PCR tests, and 16S ribosomal RNA PCR for bacterial pathogens that may be missed by targeted assays 1

Empiric antimicrobial therapy should be continued in patients with clinical features suggestive of meningitis despite negative BioFire results, especially if CSF parameters are abnormal 4
For suspected bacterial meningitis with negative BioFire results, recommended empiric therapy includes ceftriaxone or cefotaxime, with addition of ampicillin/amoxicillin for patients aged 60 or over and immunocompromised patients, and consideration of vancomycin if penicillin-resistant pneumococci are suspected 1

The timing of lumbar puncture in relation to symptom onset or antimicrobial administration can affect test sensitivity, and should be taken into account when interpreting results 2
The possibility of partially treated bacterial meningitis should not be overlooked, which can present with lymphocytic predominance in CSF and negative molecular tests 3