A 3-year-old child fell acutely ill, body temperature rose up to 39,5°C, the child became inert, there appeared recurrent vomiting, headache. Examination revealed positive meningeal symptoms, after this lumbal puncture was performed. Spinal fluid is turbid, runs out under pressure, protein concentration is 1,8 g/l; Pandy reaction is, sugar concentration is 2,2 millimole/l, chloride concentration - 123 millimole/l, cytosis is 2, 35 × 109 (80% of neutrophils, 20% of lymphocytes). What is the most probable diagnosis?