PaEasy Emergency Medicine Practice Exam

In adolescents and young adults, bacterial meningitis is most often due to Neisseria meningitidis. The fever and confusion fit meningitis, and the petechial rash is a clue pointing toward meningococcemia, since this organism can invade the bloodstream and cause widespread small-vessel bleeding. The CSF profile—high white blood cell count with neutrophil predominance, elevated protein, and low glucose—fits bacterial meningitis in general, and the combination with the rash makes meningococcal origin especially likely.

Haemophilus influenzae type b is more common in younger children, and while it used to be a frequent cause of meningitis, vaccination has greatly reduced its incidence in older kids and teens. Mycobacterium tuberculosis causes TB meningitis, which typically has a more indolent, subacute course rather than abrupt fever with a rash. Coxsackievirus B leads to viral meningitis, which usually shows a lymphocytic CSF with normal glucose and lacks the petechial rash seen in meningococcemia.

So the presentation most strongly points to Neisseria meningitidis as the cause.