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Am Fam Physician. 2002;65(6):1173-1176

The remarkable success of universal childhood immunization for Haemophilus influenzae type B and the recent introduction of an infant regimen for Streptococcus pneumoniae vaccination are shifting the epidemiology of meningitis from a childhood disease to one that occurs mainly in adults. Older adults are not the most common age group affected by meningitis, but their higher rate of morbidity and atypical presentation make for unique challenges. Choi presents an updated review of bacterial meningitis in older adults.

While viral etiologies for meningitis are common in younger adults, these relatively benign agents are much less frequent among older persons. The most common bacterial causes of meningitis in the elderly are S. pneumoniae, Listeria monocytogenes, gram-negative bacilli (especially Escherichia coli and Klebsiella pneumoniae), and Streptococcus agalactiae (group B Streptococcus). Neisseria meningitidis and H. influenzae are not common.

OrganismAntibiotic (total daily dosage)
Unknown (suspected diagnosis)*Cefotaxime, 8 to 12 g, or ceftriaxone, 4 g, plus ampicillin, 12 g
Streptococcus pneumoniae
MIC: ≤ 0.1 μg per mLPenicillin G, 20 to 24 million units
MIC: 0.1 to 1.0 μg per mLCefotaxime, 8 to 12 g, or ceftriaxone, 4 g
MIC: ≥ 1.0 μg per mLVancomycin, 2 g, plus ceftriaxone, 4 g
Listeria monocytogenesAmpicillin, 12 g, plus an aminoglycoside: gentamicin, tobramycin, 3 to 5 mg per kg
Neisseria meningitidesPenicillin G, 20 to 24 million units, or ampicillin, 12 g
Haemophilus influenzaeCefotaxime, 8 to 12 g, or ceftriaxone, 4 g
Enterobacteriaceae (gram-negative bacilli)Cefotaxime, 8 to 12 g, or ceftriaxone, 4 g†

The less common occurrence of the typical presenting symptoms of meningitis among older adults requires a higher index of suspicion to successfully detect infection. The author notes, however, that at least one classic finding is present in more than 99 percent of cases. Meningitis is very unlikely in an older patient without fever, neck stiffness, or confusion. The author advocates obtaining a lumbar puncture in most cases, unless there is concern for possible cerebral herniation from known or suspected brain tumor, abscess, or brain edema from a recent stroke. In such cases, a computed tomographic scan of the brain may be warranted before lumbar puncture is considered.

The cerebrospinal fluid (CSF) findings that strongly predict a bacterial cause include a white blood cell count greater than 500 per mm3 (500 × 106 per L), a differential with greater than 85 percent polymorphonuclear leukocytes, and a CSF glucose level that is less than one third of the serum value. Gram stain can often identify the causative organism and thus guide initial therapy, but it is less reliable for detection of Listeria and gram-negative bacilli, which are important causes of bacterial meningitis in older adults.

Drug-resistant S. pneumoniae and the possibility of Listeria infection complicate the choice of initial therapy (see the accompanying table). The author suggests using ceftriaxone or cefotaxime, plus ampicillin (for Listeria infection), if the Gram stain does not show streptococcal infection. Vancomycin is substituted for ampicillin if streptococcal organisms are visible on the stain. Use of steroids as adjunctive therapy is not routinely recommended, unless there is evidence of increased intracerebral pressure.

Given the higher morbidity in older patients with meningitis, even with prompt treatment, the author notes that preventive measures are obviously important. Previous immunization with the adult pneumococcal vaccine is not completely effective in preventing meningitis but appears to cut the risk by at least one half. Listeriosis is usually caused by contaminated food. A vaccine for group B streptococcal infection is in research but is intended for prevention of neonatal disease, and trials in older adults are not ongoing.

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