Infectious Diseases II
Bacterial meningitis has community-acquired or health careβassociated epidemiology; health careβ
associated meningitis is usually associated with neurotrauma or neurosurgical procedures.
people. The incidence has been decreasing, likely because of increased vaccination against common
pathogens. The incidence of nosocomial bacterial meningitis varies depending on the mechanism of
neuro-anatomic disruption and ranges from 1.5% of patients undergoing craniotomy to 25% of post-
trauma patients with basilar skull fracture.
Delayed CSF sterilization beyond 24 hours is a risk factor for subsequent neurologic sequelae, including
intracranial hypertension, seizures, and permanent neurologic deficit. Clinical presentations of septic
shock, altered mental status, and seizures are associated with worse outcomes. Additional complications
include respiratory failure and hyponatremia.
Crude mortality for community-acquired meningitis is 19%β37%, whereas mortality for health careβ
associated meningitis is generally lower, particularly if associated with a reversible procedure or
removable device.
The clinical diagnosis of meningitis is nonspecific and difficult to distinguish from that of other
infections. Although headache, fever, neck stiffness, and altered mental status are present in almost
95% of patients with community-acquired meningitis, fever and a decreased level of consciousness are
the most consistent clinical features in patients with health careβassociated meningitis.
analysis, as well as Gram stain and culture, is necessary for definitive diagnosis. Neuroimaging with
head computed tomography to detect prelumbar brain shift and risk of brain herniation should be done
before lumbar puncture in patients with suspected cranial mass (e.g., immunosuppressed, papilledema,
history of CNS disease, new-onset seizure, and focal neurologic deficit).
Opening pressure during lumbar puncture is usually increased in bacterial meningitis; it is usually
in the range of 200 to 500 cm H2O (normal opening pressure in adults: 10β20 cm H2O).
Cell count and fluid analysis
Community-acquired bacterial meningitis can be differentiated from other causes of
meningitis (e.g., viral, aseptic). In general, bacterial meningitis is associated with CSF that is
predominantly neutrophilic and has lower glucose concentration. Strong predictors of bacterial
meningitis include:
| (a) | CSF glucose less than 40 mg/dL |
|---|---|
| (b) | Ratio of CSF to blood glucose less than 0.6 |
| (c) | CSF protein greater than 220 mg/dL |
| (d) | CSF WBC greater than 100 to 1000 cells/ΞΌL |
| (e) | CSF leukocyte count greater than 2000 cells/mm3 |
| (f) | CSF neutrophil count greater than 1180 cells/mm3 |
ii.
The diagnostic utility of CSF cell count and fluid analysis in health careβassociated meningitis
is unknown but is likely limited because of concomitant reasons for local inflammation related
to devices or recent procedures. In the presence of CSF drains or recent history of neurosurgery,
new headache, nausea, lethargy, and/or change in mental status may be a sign of new CNS
infection. Neither normal CSF analysis nor negative Gram stain may exclude the presence of
an infection. Elevated CSF lactate concentration may be useful to distinguish meningitis from
other infectious sources.