[Acute meningitidis, acute phase proteins and procalcitonin]

The prognosis of bacterial meningitis is critically dependent on a rapid causal diagnosis and implementation of an accurate treatment. However, clinical and biological parameters available within the few hours that follow the patient's admission are not reliable enough, except when bacteria are to be found in cerebrospinal fluid under the microscope. Therefore, the initial treatment of acute meningitis is still most of time presumptive so that the definitive diagnosis, however difficult, is often established when the therapeutic management has already been initiated. The use of biological markers, especially lymphokines and acute-phase proteins, has been proposed to facilitate the accuracy of the initial diagnosis. Today, C-reactive protein (CRP) is the most widely used inflammatory marker in emergency departments with aim to discriminate bacterial from viral infections. In 1998, Gerdes et al. published a meta-analysis from 35 studies questioning the usefulness of CRP in discriminating bacterial meningitis from viral meningitis. They outlined that the majority of authors proposed to use this inflammation marker as an additional tool for discriminating bacterial meningitis from viral meningitis, without having evaluated its independent contribution relative to other parameters such as white blood cell count, cerebrospinal fluid (CSF) white cell count, protein or glucose. Procalcitonin (PCT) is an acute-phase protein with faster kinetics than CRP, its concentration in serum rising within the few hours that follow the inception of a bacterial infection. Two French studies published in 1997 and 1998 have shown that, using a cut-off range of 0.5 through 2 ng/mL, the sensitivity and specificity of PCT were 100% in discriminating bacterial meningitis from viral meningitis. Some of the seven studies published since seemed to demonstrate the usefulness of PCT in diagnosing meningitis. Finally, PCT was used effectively to shorten unnecessary antibiotic treatment for children seen in an hospital in Paris (France) during summer 2000.