Pathogens most frequently involved in immunocompetent adults are Streptococcus pneumoniae (“pneumococcus,” ~50%) and Neisseria meningitidis (“meningococcus,” ~25%). Predisposing factors for pneumococcal meningitis include infection (pneumonia, otitis, sinusitis), asplenia, hypogammaglobulinemia, complement deficiency, alcoholism, diabetes, and head trauma with CSF leak. Listeria monocytogenes is a consideration in pregnant women, individuals >60 years, alcoholics, and immunocompromised individuals of all ages. Enteric gram-negative bacilli and group B streptococcus are increasingly common causes of meningitis in individuals with chronic medical conditions. Staphylococcus aureus and coagulase-negative staphylococci are causes following neurosurgical procedures, especially shunting procedures for hydrocephalus.
Presents as an acute fulminant illness that progresses rapidly in a few hours or as a subacute infection that progressively worsens over several days. The classic clinical triad of meningitis is fever, headache, and nuchal rigidity (“stiff neck”). Mental status changes occur in >75% of pts and vary from lethargy to coma. Nausea, vomiting, and photophobia are also common. Seizures occur in 20-40% of pts. Raised intracranial pressure (ICP) is the major cause of obtundation and coma. The rash of meningococcemia begins as a diffuse maculopapular rash resembling a viral exanthem but rapidly becomes petechial on trunk and lower extremities, mucous membranes and conjunctiva, and occasionally palms and soles.
The CSF profile is shown in Table 191-1. CSF bacterial cultures are positive in >80% of pts, and CSF Gram's stain demonstrates organisms in >60%. A 16S rRNA conserved sequence broad-based bacterial PCR can detect small numbers of viable and nonviable organisms in the CSF and is useful for diagnosis in pts pretreated with antibiotics and when Gram's stain and CSF cultures are negative. When positive, more specific PCR tests for individual organisms can be obtained. The latex agglutination (LA) test for detection of bacterial antigens of S. pneumoniae, N. meningitidis, Haemophilus influenzae type b, group B streptococcus, and Escherichia coli K1 strains in the CSF is being replaced by the CSF bacterial PCR assay. The Limulus amebocyte lysate assay rapidly detects gram-negative endotoxin in CSF and thus is useful in diagnosis of gram-negative bacterial meningitis; false-positives may occur but sensitivity approaches 100%. Petechial skin lesions, if present, should be biopsied. Blood cultures should always be obtained.
Includes viral meningoencephalitis, especially herpes simplex virus (HSV) encephalitis (see below); rickettsial diseases such as Rocky Mountain spotted fever (immunofluorescent staining of skin lesions); focal suppurative CNS infections including subdural and epidural empyema and brain abscess (see below); subarachnoid hemorrhage (Chap. 18. Subarachnoid Hemorrhage); and the demyelinating disease acute disseminated encephalomyelitis (ADEM, Chap. 190. Multiple Sclerosis).
Treatment: Acute Bacterial Meningitis
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Moderate or severe sequelae occur in ~25% of survivors; outcome varies with the infecting organism and can include decreased intellectual function, memory impairment, seizures, hearing loss and dizziness, and gait disturbances.
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