Infectious Diseases II

Gram stain and culture: Bacteriologic examination of CSF can provide rapid and reliable

identification of the causative pathogen(s). Although CSF cell count and analysis is the diagnostic

foundation for community-acquired meningitis, CSF culture is the most specific test for health

care–associated meningitis. Of note, immunocompromised patients with meningitis may present

with normal CSF cell counts.

Appropriate empiric antibiotic therapy administered intravenously, targeted against likely pathogens,

and guided by local antibiotic susceptibility patterns should be initiated as soon as possible after bacterial

meningitis is suspected. See Table 3 for common pathogens and recommended empiric therapy.

to bacterial minimum inhibitory concentration (MIC) and antibiotic pharmacodynamic (PD) properties.

Although meningeal inflammation may promote CSF penetration, data are inconsistent regarding its

impact on effective antimicrobial delivery. Furthermore, as meningitis improves, inflammation will

likely improve, and there is currently no way to predict the level of penetration in correspondence to the

severity of the inflammation.

Gram stain can be used to broaden bacterial coverage, but final culture should be reserved for antibiotic

de-escalation and definitive antibiotic regimen.

Role of corticosteroids

Adjunctive corticosteroids may improve outcomes by reducing reactive meningeal inflammation

and neurologic sequelae related to antibiotic-induced bacterial lysis.

Conflicting results are published regarding the effects of systemic corticosteroids on neurologic

sequelae and mortality among patients with bacterial meningitis.

Studies from high-income countries tend to suggest that systemic corticosteroids decrease or trend

toward a decrease in mortality and neurologic sequelae.

with Streptococcus pneumoniae meningitis. However, because corticosteroids must be administered

before the receipt of antimicrobials, it is unlikely that clinicians will know the etiology of the

disease when making the decision for steroids.

The IDSA guidelines recommend administering dexamethasone 0.15 mg/kg every 6 hours for

up to 96 hours, with the first dose administered 10–20 minutes before, or at least concomitant

with, the first dose of antimicrobial therapy. The IDSA guidelines also recommend continuation of

dexamethasone only if cultures show the presence of S. pneumoniae, although this recommendation

is not supported by strong clinical evidence.

Health care–associated meningitis

See Table 3 for recommended empiric treatment of health care–associated meningitis.

In patients with CSF shunts, complete removal of an infected CSF shunt and replacement with an

external ventricular drain combined with intravenous antimicrobial therapy is recommended.

In selected patients with bacterial meningitis after placing a CSF shunt, the IDSA recommends

direct instillation of antimicrobial agents intraventricularly through either an external

ventriculostomy or shunt reservoir. This practice should only be considered in patients with

pathogens that are difficult to eradicate or for those who cannot undergo catheter replacement.

See Table 4 for selected antimicrobial intraventricular dosing. When intraventricular antibiotics

are administered, drains should be clamped for 15-60 minutes to allow antibiotics to equilibrate

throughout the CSF. Antimicrobial agents administered into the CNS should be preservative free.

Dosing and intervals of intraventricular antimicrobial therapy should be adjusted on the basis of the

CSF antimicrobial concentration being 10-20 times the MIC of the causative pathogen, ventricular

size, and daily output from ventricular drain. Given the paucity of pharmacokinetic (PK) data