Aciclovir Versus Placebo for HSV-2 Meningitis

Inclusion Criteria: * Adults ≥18 years of age admitted on suspicion of viral meningitis defined as: 1. A clinical presentation consistent with viral meningitis (e.g. headache, nuchal rigidity, photophobia, or fever) AND 2. Cerebrospinal fluid (CSF) pleocytosis (\>4 leukocytes x 106/L) AND 3. HSV-2 positive by PCR of the CSF 4. Glasgow Coma Scale score of 15 AND 5. Ability to absorb oral medications Exclusion Criteria: * Patients fulfilling any of the following criteria will be excluded: 1. Encephalitis as defined by the International Encephalitis Consortium if diagnosed during standard care (see Glossary)20 2. Transverse myelitis as defined by the Transverse Myelitis Consortium Working Group if diagnosed during standard care (see Glossary)21 3. Severe immuno-compromise defined as an ongoing need for biological- or chemotherapy (e.g. natalizumab), prednisolone \>20 mg/day for ≥14 days, uncontrolled HIV/AIDS (see glossary), haematological malignancies, and organ transplant recipients14,18,22 4. Moderate to severe concomitant genital herpes requiring systemic aciclovir 5. Pregnancy (proven by positive urine or plasma human chorionic gonadotropin test in fertile women) 6. Hepatic impairment (aspartate aminotransferase or alanine aminotransferase levels \>5 times the upper limit of normal) 7. Impaired renal function (estimated glomerular filtration rate \<25 mL/min) 8. Intolerance to (val)aciclovir 9. Probenecid treatment 10. Systemic antiviral therapy with an antiherpetic effect for \>24 hours 11. Previous enrolment into this trial