Most often due to viruses - enteroviruses, herpes simplex, VZV (PCR tests available) and mumps. The seroconversion illness of HIV can present with aseptic meningitis.
Many treatable and serious problems cause a similar CSF picture e.g., partially treated bacterial meningitis, TB, fungi, syphilis, leptospirosis, neoplasia, drugs, cyst related, Mollaret's, SLE, Behçet's, sarcoidosis, amoeba, and others. Accurate cytology essential.
Approach to the patient:
Obtain careful history including travel, exposure to other individuals with similar illness, animals, tuberculosis, sexual activity, drugs.
For patients with suspected bacterial meningitis based on CSF findings, antibiotics should be initiated promptly.
Patients with probable viral meningitis (CSF WBC count <500, >50% mononuclear cells, protein <0.8 g/L, normal glucose and negative Gram stain) may be observed without antibiotic therapy.
However if patients are elderly, immunocompromised or have received prior antibiotics, they should be given antibiotics.
When it is not clear if it is a viral or bacterial process, patients may be observed without antibiotics or given antibiotics. Repeat lumbar puncture may be useful.
Specific treatment is necessary for meningitis due to primary HSV, VZV, leptospirosis, syphilis, fungi and TB.