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Meningitis: Inflammation of the meninges, the membranes covering the brain and spinal cord

Encephalitis: Inflammation of the brain parenchyma



  • Bacteria:

    • Group B Streptococcus (52%)

    • Escherichia coli and other gram-negative bacilli (rods) (27%)

    • Listeria monocytogenes (6%)

    • Anaerobes (3%)

    • Other gram-positive organisms (7%): enterococci, Streptococcus pneumoniae, staphylococci

    • Other gram-negative organisms (5%): Haemophilus influenzae, Neisseria meningitides, Pseudomonas

  • Viruses: Herpes simplex virus (HSV), human herpesvirus 6 (HHV-6), enteroviruses, arboviruses, human immunodeficiency virus (HIV), adenovirus, varicella zoster virus (VZV), Epstein-Barr virus (EBV), cytomegalovirus (CMV), measles, mumps, rubella, influenza, parainfluenza, parvovirus B19, rotavirus, others


  • Bacteria:

    • S. pneumoniae and N. meningitidis (90%–95%)

    • Other organisms: H. influenzae, Salmonella species, group B Streptococcus, L. monocytogenes, anaerobes

  • Viruses: Enteroviruses, arboviruses, HSV, HHV-6, HIV, adenovirus, VZV, EBV, CMV, measles, mumps, rubella, influenza, parainfluenza, parvovirus B19, rotavirus, zoonotic diseases, arthropod-borne diseases, others


  • Mycoplasma tuberculosis: Consider based on history of exposure

  • Fungi: Immunocompromised patients

  • Parasites and protozoa: Consider based on history of exposure

  • Rabies: Consider based on history of exposure

Enteroviruses account for 85% to 95% of viral meningoencephalitis in which an etiologic agent is identified.



  • Fever of unknown origin

  • Vomiting, poor feeding, failure to thrive (FTT)

  • Apnea or respiratory distress

  • Altered mental status: irritability or lethargy

  • Signs of increased intracranial pressure (ICP): bulging fontanelle

  • Focal neurologic deficits

  • Seizures

  • Petechiae/purpura or rash

  • Shock


  • Fever: almost always present

  • Nausea/vomiting

  • Headache, photophobia

  • Back pain

  • Altered mental status

  • Focal neurologic deficits

  • Seizures

  • Signs of increased ICP: papilledema (if present, look for brain abscess, venous sinus thrombosis, and subdural fluid collection/empyema)

  • Signs of meningeal irritation: positive Kernig's and Brudinski's signs

  • Petechiae/purpura or rash

  • Shock



  • Serum tests: abnormal white blood cell (WBC) count (leukocytosis or leukopenia), prominence of atypical lymphocytes (EBV), viral studies

  • Cerebrospinal fluid (CSF) studies: cell count, WBC differential, glucose, protein, Gram stain, culture, viral studies (enterovirus polymerase chain reaction [PCR], HSV PCR, etc.), acid-fast bacillus AFB stain, tuberculosis culture – See Table 44-1

  • Blood culture: positive in 80% to 90% of patients with suspected bacterial meningitis who were not pretreated with antibiotics

  • Nasopharyngeal swab: For viral studies

TABLE 44-1

Cerebrospinal Fluid Analysis

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