In cases of meningitis caused by external ventricular catheters (EVDs), which are the most commonly placed intracranial catheters that can lead to central nervous system infection through contamination/colonisation, the diagnosis may not be differentiated by either clinical signs and symptoms or conventional cerebrospinal fluid (CSF) tests. Therefore, due to the limitations in diagnosis and prognostic prediction of EVD-induced meningitis and the high mortality/morbidity rates of the disease, markers with high sensitivity and specificity in post-operative meningitis are needed. Calcitonin gene-related peptide (CGRP), a neuropeptide, has been shown to increase when C or Aδ sensory fibres are damaged or in the presence of inflammation in tissues adjacent to the fibres. CGRP is localised in nociceptive nerve terminals together with another neuropeptide, substance P, which has similar biological effects. There are very few studies investigating how CGRP levels in CSF and serum change in bacterial meningitis. Although it is thought that nociception and neuroimmune interactions affect meningeal antibacterial host defence, that nociceptors signal via CGRP to meningeal immune cells during infection, and that this neuroimmune axis exacerbates bacterial meningitis by weakening host defence, it is not yet clear how CGRP and substance P levels affect disease prognosis. This study will evaluate the utility of CGRP and substance P levels as biomarkers to assess diagnosis and treatment response in patients with post-operative meningitis followed in the intensive care unit.