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or a contiguous infection such as sinusitis or otitis media.

Changes in epidemiology have mirrored vaccination

practices in children and adults against Haemophilus influ ­

enzae, S. pneumoniae, and N. meningitidis. Routine childhood vaccination against H. influenza type b has helped

decrease this pathogen as a cause of meningitis. Use of the

pneumococcal vaccine in adults may be reducing the rate

of S. pneumoniae disease. Given the success of routine

childhood vaccination programs, over the past 25 years,

the median age of a patient diagnosed with meningitis has

risen from 15 months to 42 years of age.

Aseptic meningitis is due to inflammation from other

causes such as drugs, rheumatologic conditions, or nonbacterial infections. Most cases are caused by viral (the

most common overall causes of meningitis) or mycobacterial infections. Of the viral etiologies, enteroviruses and

echoviruses are the most common, but herpes simplex

virus (HSV) is an important pathogen.

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CHAPTER 35

Encephalitis i s a n infection of the brain parenchyma

causing inflammation within the CNS. Viral pathogens

include HSV, which is the most treatable cause of encephalitis. In the acute care setting, it can be difficult to distinguish encephalitis from severe cases of bacterial meningitis,

as patients' signs and symptoms may be similar.

CLINICAL PRESENTATION

.... History

The classic triad of meningitis includes fever, neck stiffness, and altered mental status, but all of these are present

together in less than half of adult patients with bacterial

meningitis. Patients may also experience seizure. Many of

the symptoms are nonspecific, such as headache, nausea

and vomiting, and neck pain, making accurate diagnosis

challenging.