A 3-year-old boy is brought to the emergency department by his parents due to a high fever and irritability. He has had a runny nose and cough for the past two days. On examination, he is lethargic and has a bulging fontanelle. A lumbar puncture is performed, and the cerebrospinal fluid (CSF) analysis shows elevated protein, low glucose, and a high white cell count with a predominance of neutrophils. What is the most likely diagnosis?