According to the fact that only bacterial meningitis and meningoencephalitis can induce confusion, and the lack of interest for the diagnosis of Kernig's sign, nuchal rigidity, and headache, improvement of the mental and hemodynamic status are the BEST and alone scale for evaluating the clinical response of meningitis. Do not forget that a second lumbar puncture is usefull within the three-four days of treatment in case of doubt.
You may look at our paper published in Intensice care Medecine ( 2005) concerning the "Accuracy of clinical presentation for diffrentiating bacterial from viral meningitis ..."; (full on my contributions-publications).