Pneumococcal Meningitis

Essentials of Diagnosis

Fever, headache, altered mental status.

Meningismus.

Gram-positive diplococci on Gram stain of cerebrospinal fluid.

General Considerations
S pneumoniae is the most common cause of meningitis in adults. Head trauma, with cerebrospinal fluid leaks, sinusitis, and pneumonia may precede it.
Clinical Findings
SYMPTOMS AND SIGNS
The onset is rapid, with fever, headache, meningismus, and altered mentation. Pneumonia may be present. Compared with meningitis caused by the meningococcus, pneumococcal meningitis lacks a rash, and focal neurologic deficits, cranial nerve palsies, and obtundation are more prominent features.
LABORATORY FINDINGS
The cerebrospinal fluid typically has more than 1000 white blood cells per microliter, over 60% of which are polymorphonuclear leukocytes; the glucose concentration is less than 40 mg/dL, or less than 50% of the simultaneous serum concentration; and the protein usually exceeds 150 mg/dL. Not all cases of meningitis will have these typical findings, and alterations in cerebrospinal fluid cell counts and chemistries may be surprisingly minimal, overlapping with those of aseptic meningitis.
Gram stain of cerebrospinal fluid shows gram-positive cocci in 80–90% of cases, and in untreated cases blood or cerebrospinal fluid cultures are almost always positive.
Treatment
Antibiotics should be given as soon as the diagnosis is suspected. If lumbar puncture must be delayed (eg, while awaiting results of an imaging study to exclude a mass lesion), the patient should be treated empirically for presumed meningitis with intravenous ceftriaxone, 2 g, plus vancomycin, 15 mg/kg, plus dexamethasone, 0.15 mg/kg administered concomitantly after blood cultures (positive in 50% of cases) have been obtained. Once susceptibility to penicillin has been confirmed, penicillin, 24 million units intravenously daily in six divided doses, or ceftriaxone, 2 g every 12 hours intravenously, is continued for 10–14 days in documented cases.
The best therapy for penicillin-resistant strains is not known. Penicillin-resistant strains often are cross-resistant to the third-generation cephalosporins as well as other antibiotics. Susceptibility testing is essential to proper management of this infection. Treatment failures have been reported with ceftriaxone or cefotaxime for meningitis caused by strains with penicillin MICs
2 mcg/mL. If the MIC of ceftriaxone or cefotaxime is
0.5 mcg/mL, single-drug therapy with either of these cephalosporins is likely to be effective; when the MIC is
1 mcg/mL, treatment with a combination of ceftriaxone, 2 g intravenously every 12 hours, plus vancomycin, 30 mg/kg/d intravenously in two or three divided doses, is recommended. If a patient with a penicillin-resistant organism is slow to respond clinically, repeat lumbar puncture may be indicated to assess bacteriologic response.
Dexamethasone administered with antibiotic to adults has been associated with a 60% reduction in mortality and a 50% reduction in unfavorable outcomes, primarily in patients with pneumococcal meningitis. It is recommended that adults with acute bacterial meningitis be given 10 mg of dexamethasone intravenously immediately prior to or concomitantly with the first dose of appropriate antibiotic and continued in those with pneumococcal disease every 6 hours thereafter for a total of 4 days. The effect of dexamethasone on outcome of meningitis caused by penicillin-resistant organisms is not known.

Torpy JM et al. JAMA patient page. Pneumococcal diseases. JAMA. 2006 Apr 12;295(14):1730. http://jama.ama-assn.org/cgi/content/full/295/14/1730 [PMID: 16609100]

Weisfelt M et al. Dexamethasone treatment in adults with pneumococcal meningitis: risk factors for death. Eur J Clin Microbiol Infect Dis. 2006 Feb;25(2):73–8. [PMID: 16470361]