A 14-month-old boy is brought in by his parents with fever, fussiness and lethargy, and apparent headache. On examination, the neck is stiff. His parents have not allowed his routine childhood vaccines. Very short Gramnegative rods are seen in the CSF, so antibiotics are immediately started. The organism grows on chocolate agar but not blood agar. No one else in the family is ill. What is the most likely causative agent?
A) Escherichia coli B) Haemophilus influenzae type b C) Klebsiella pneumoniae D) Neisseria meningitidis E) Streptococcus pneumoniae