Clinical Features

The clinical case definition of meningitis is a sudden onset of fever (>38.0 ^oC axillary) and one of the following:

• neck stiffness
• altered consciousness
• other meningeal sign
• haemorrhagic rash.

In patients less than 1 year of age meningitis is suspected when fever is accompanied by a bulging fontanelle.

Case classification of bacterial meningitis

Cases of meningitis are classified as suspected, probable or confirmed.¹

• Suspected cases: any patient with sudden onset of fever (>38.0 ^oC axillary) and either neck stiffness, altered consciousness or other meningeal sign. 
• Probable cases: a suspected case in which CSF examination reveals a turbid appearance; leukocytosis with >100 cells/mm³; or leukocytosis with 10–100 cells/mm³ and an elevated protein concentration (>100 mg/dL) or decreased glucose concentration (<40 mg/dL). 
• Confirmed cases: a bacterial pathogen has been identified in the CSF by either culturing the pathogen or by identifying the pathogen by Gram stain or by antigen detection methods.

It is important that any bacterial pathogen is identified from CSF or blood (normally sterile fluids) as identification of H. influenzae, N. meningitidis or S. pneumoniae from non-sterile sites, such as the throat, does not confirm bacterial meningitis, as these bacteria can be present in these non-sterile areas without causing disease.