Bacterial Meningitis

Meningitis can be acute, subacute, or chronic. In otherwise healthy children, the three most common organisms causing acute bacterial meningitis are Streptococcus pneumoniae, Neisseria meningitidis, and Haemophilus influenzae type b (Hib). Isolation of an organism other than these three organisms from the CSF of a child older than 2 months always requires an explanation or evaluation for unusual host susceptibility. Children with cochlear implants, asplenia, HIV infection, or CSF leak from basilar skull or cribriform fracture are at greater risk for pneumococcal meningitis. Deficiencies in terminal components of complement lead to greater risk for meningococcal infection (Saez-Llorens and McCracken, 2008). In adults, the common etiologic agents of acute meningitis include S. pneumoniae, N. meningitidis, and Listeria monocytogenes.

Patients with acute meningitis most often present with fever, headache, meningismus, and altered mental status. Infants can present with nonspecific symptoms such as inconsolable crying, irritability, nausea, vomiting, and diarrhea. Lethargy, anorexia, and grunting respirations indicate a critically ill infant. Older children may complain of headache, vomiting, back pain, myalgia, and photophobia; may be confused or disoriented; and may verbalize specifically that the neck is stiff or sore. Seizures are noted in up to 20% to 30% of children before hospital admission or early in the course of the illness.

In contrast, patients with subacute or chronic meningitis may have the same symptoms with a much more gradual onset, lower fever, and associated lethargy and disability. Mycobacterium tuberculosis, Treponema pallidum (syphilis), Borrelia burgdorferi (Lyme disease), and fungi (e.g., Crypto-coccus neoformans, Coccidioides spp.) are the most common agents (Tunkel et al., 2010).

Physical examination should look for papilledema, middle ear and sinus infections, petechiae (common with N. meningitidis), nuchal rigidity, and in infants, a bulging fontanel. Blood cultures should be taken. A lumbar puncture (LP) for CSF analysis should be done as soon as possible. A brain CT scan before LP is not necessary if the patient has no evidence of immunocompromise, CNS disease, new seizure, papilledema, altered consciousness, or focal neurologic deficit, and if a subarachnoid hemorrhage is not suspected. If neuroimaging is necessary, blood cultures should be taken and antibiotics given before the study; a delay in administration of antibiotics leads to a worse outcome. CSF should be sent for cell count, WBC differential, glucose, protein, and Gram stain with culture. Acid-fast bacilli stain and cryptococ-cal antigen may be obtained when indicated.

Empiric antibiotics for the initial treatment of bacterial meningitis are listed in Table 16-20, but these should be tailored to the isolated organisms whenever possible. Adjunctive dexamethasone is recommended for children and infants with Hib meningitis, but not if they have already received antibiotics. In adults, adjunctive dexamethasone is recommended for pneumococcal meningitis (Tunkel et al., 2004). Close contacts of patients with N. meningitidis should receive rifampin, 20 mg/kg (not to exceed 600 mg) twice daily for 2 days, or ciprofloxacin, 500 mg as a single dose, or ceftriaxone, 250 mg IM as a single dose. Unimmunized persons exposed to H. influenzae meningitis should receive rifampin (Turkel et al., 2010). Pregnant women should not receive rifampin or doxycycline.

A repeat LP should be done if no clinical response is seen after 48 hours of appropriate antibiotic therapy, particularly for patients with resistant pneumococcal disease and those who received dexamethasone. Neonates with gram-negative bacilli and patients with ventriculoperitoneal (VP) shunts require documentation of CSF sterility. The duration of antimicrobial therapy is 7 days for patients with N. meningitidis or Hib, 10 to 14 days for pneumococcal meningitis, and 14 to 21 days for Streptococcus agalactiae.

Table 16-20 Empiric Antibiotics for Initial Treatment of Bacterial Meningitis

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