A 1-year-old patient presents to the emergency room with fever, headaches, lethargy, stiff neck, and disorientation, with the absence of petechial rash. The mother noted that while her daughter was playing and eating normally that morning, later in the day she developed a non-specific fever and progressed quickly into her current state. When you ask the mother about her daughter's vaccination status, she states that she chose not to vaccinate her daughter due to her personal and religious preferences. Gram-stain analysis of the patient's cerebrospinal fluid reveals Gram-negative, encapsulated cells. Which of the following disease diagnoses is most likely?
