Background

Early empiric antimicrobial therapy is critical in suspected central nervous system (CNS) infection to reduce morbidity and mortality. Untreated bacterial meningitis is associated with extremely high mortality and untreated herpes simplex virus encephalitis is associated with severe neurological impairment or death in a substantial proportion of cases. ^{Reference MacDougall and Polk1,Reference Schwartz2} Clinical presentation frequently overlaps between meningitis and encephalitis, with fever, altered mental status and nuchal rigidity commonly observed.Reference Mailles and Stahl ³

Lumbar puncture and blood cultures are essential investigations and should not delay empiric therapy. While neuroimaging is often performed, it is not routinely required unless features of raised intracranial pressure or immunocompromise are present. Australian Therapeutic Guidelines and NSW Health recommendations advise early broad-spectrum antimicrobial coverage, typically with a third-generation cephalosporin and adjunctive agents based on patient risk factors. ^4,5 Aciclovir is recommended when herpes simplex virus encephalitis is suspected.

Decisions regarding antimicrobial de-escalation remain variable in clinical practice. While guidelines support narrowing therapy when a pathogen is identified, recommendations for cessation when cerebrospinal fluid findings are normal or non-diagnostic are less explicit. Although syndromic PCR assays have short analytical run-times, the clinically relevant turnaround time extends beyond assay run-time to include preanalytical and postanalytical processes such as specimen transport, batching and result reporting. ^{Reference Rafiei, Subedi, Harris and Paterson6} Delays across this pathway may reduce the practical stewardship benefit of multiplex PCR testing, particularly in regional hospital networks reliant on off-site laboratories. ^{Reference Messacar, Parker, Todd and Dominguez7}