Chapter 128: Central Nervous System Infections

KEY CONCEPTS

• The four most common causative pathogens of acute community-acquired bacterial meningitis in the United States are Streptococcus pneumoniae, group B Streptococcus, Neisseria meningitidis, and Haemophilus influenzae type b, although routine vaccinations are having a dramatic effect on the incidence and distribution of these pathogens.

• In cases of bacterial meningitis, initial findings can include (a) presenting signs and symptoms: fever, headache, nuchal rigidity (the classic triad), Brudzinski’s or Kernig’s sign, and altered mental status; and (b) abnormal cerebrospinal fluid (CSF) chemistries: elevated white blood cell (WBC) count (>1,000 cells/mm³ [1.0 × 10⁹/L]), elevated protein (>50 mg/dL [500 mg/L]), and decreased glucose levels (<45 mg/dL [2.5 mmol/L]).

• Main microbiologic tests that should be obtained include Gram stain and culture of the CSF and blood. In patients with negative CSF Gram stain and culture, molecular testing such as polymerase chain reaction (PCR) has additive value in the pathogen(s) identification.

• Three primary goals of treatment in meningitis include (a) eradication of infection, (b) amelioration of signs and symptoms, and (c) prevention of the development of neurologic sequelae, such as seizures, deafness, coma, and death.

• When selecting antibiotics, the clinician must consider the antibiotic concentration at the site of infection and the spectrum of antibacterial activity. Empirical choices should be based on age, predisposing conditions, vaccination history, comorbidities, and local susceptibility patterns.

  (a) Either ceftriaxone or cefotaxime with vancomycin is a reasonable initial choice for empirical coverage of community-acquired meningitis in adult patients. (b) Meningitis due to Listeria monocytogenes is more common in infants and elderly. Therefore, ampicillin—with or without gentamicin—should be empirically added to antimicrobial regimens in these age groups.

• Empirical coverage with an appropriate antibiotic should be started as soon as possible when clinical suspicion of meningitis exists. If there is a delay in obtaining a lumbar puncture (even 30-60 minutes), or if the patient is to undergo neuroimaging, the first dose of antibiotic(s) should not be withheld.

• Antibiotic dosages for the treatment of meningitis should be optimized to ensure adequate CNS therapeutic concentrations.

• The duration of antibiotic treatment for acute bacterial meningitis has not been standardized. However, it is generally based on the causative organism and the individual case, and may range from 7 to 21 days.

• Close contacts and relatives of the index case should be assessed for appropriate chemoprophylaxis and vaccinations, particularly for N. meningitidis and H. influenzae meningitis.

• Steroid treatment includes dexamethasone of 0.15 mg/kg per dose given four times daily for 2 to 4 days in infants and children with proven or strongly suspected H. influenzae type b meningitis. Steroids should be started 10 to 20 minutes prior to, or at least concomitant with, the first dose of antibiotics.