A 5-year-old girl was admitted on February 10 with fever, headache, vomiting for 4 days, and restlessness for 1 day. Examination: temperature 39.3°C, pulse 123/min, restlessness, neck stiffness, multiple petechiae on the abdomen, Kernig's sign (+), Brudzinski's sign (-). CBC: WBC 17×10<sup>9</sup>/L (N 89%). CSF: pressure 312mmH<sub>2</sub>O, cell count 2.4×10<sup>12</sup>/L (N 95%), protein 1.65g/L, glucose 1.5mmol/L, chloride 89mmol/L. The most likely diagnosis is: