INFECTIOUS SYNDROMES

Meningitis

Classification: Inflammation of the meninges and cerebrospinal fluid, with bacterial meningitis requiring immediate empiric treatment (Fiske & Bloch, 2019; Norris, 2020).

Key diagnostic discriminator: Fever, headache, neck stiffness, altered mental status, or meningococcal-type rash should prompt rapid blood cultures, cerebrospinal fluid evaluation when safe, and immediate empiric therapy when bacterial disease is suspected (Fiske & Bloch, 2019; Smetana, 2012).

Clinical priority: Purpura, shock, altered consciousness, new seizure, focal deficit, papilledema, or Cushing physiology signals immediate danger (Fiske & Bloch, 2019; World Health Organization, 2025).

Etiology and risk factors

  • Etiology varies by age, exposure, immune status, vaccination, anatomy, and neurosurgical history. Key community bacterial pathogens include Streptococcus pneumoniae and Neisseria meningitidis; Listeria risk rises with older age, pregnancy, and impaired cellular immunity (Fiske & Bloch, 2019; Norris, 2020).
  • Neonatal pathogens include group B streptococci, enteric gram-negative bacilli, and Listeria. Viral, fungal, mycobacterial, spirochetal, medication-related, neoplastic, and autoimmune meningitis also occur (Fiske & Bloch, 2019; Norris, 2020).

Pathophysiology

  • Organisms reach the meninges through hematogenous spread, contiguous infection, trauma/procedure, or direct inoculation. Replication in cerebrospinal fluid triggers cytokines and neutrophilic inflammation (Fiske & Bloch, 2019; Norris, 2020).
  • Blood-brain barrier permeability, cerebral edema, vasculitis/thrombosis, impaired autoregulation, and reduced perfusion cause increased intracranial pressure and neurologic injury. Rapid bacterial lysis can transiently intensify inflammation (Fiske & Bloch, 2019; Norris, 2020).

Clinical manifestations

  • Fever, severe headache, neck stiffness, photophobia, nausea/vomiting, lethargy/confusion, seizure, focal deficit, or cranial-nerve abnormality. The classic triad is not present in every patient (Fiske & Bloch, 2019; Smetana, 2012).
  • Meningococcemia may produce petechiae or nonblanching purpura, shock, and disseminated intravascular coagulation. Infants and older adults may present nonspecifically (Fiske & Bloch, 2019; Smetana, 2012).
  • Papilledema, declining consciousness, Cushing response, or new focal deficit suggests raised intracranial pressure or herniation risk (Fiske & Bloch, 2019; Smetana, 2012).

Findings that argue against or redirect

  • Absence of neck stiffness or normal mental status does not exclude bacterial meningitis (Fiske & Bloch, 2019; Smetana, 2012).
  • Normal cerebrospinal fluid very early or after partial antibiotic treatment is possible; interpret the entire pattern and microbiology (Fiske & Bloch, 2019; Smetana, 2012).
  • Focal neurologic deficit, papilledema, new seizure, or marked impaired consciousness redirects the immediate sequence toward brain imaging before lumbar puncture, without delaying antibiotics (Fiske & Bloch, 2019; Smetana, 2012).

Diagnostic evaluation

  • Obtain blood cultures and perform lumbar puncture as soon as possible, preferably before antimicrobials, unless a contraindication or reason for deferral is present. Cerebrospinal fluid studies include opening pressure, cell count and differential, protein, glucose with paired serum glucose, Gram stain, culture with susceptibility testing, and targeted molecular testing (Fiske & Bloch, 2019; World Health Organization, 2025).
  • Do not obtain cranial imaging routinely before lumbar puncture. Image first when there is severely impaired consciousness, focal neurologic deficit, cranial-nerve deficit, papilledema, a new-onset seizure in an adult, or severe immunocompromise (Fiske & Bloch, 2019; World Health Organization, 2025).
  • If lumbar puncture is deferred, collect blood cultures and start empiric treatment before imaging. Do not delay therapy for imaging or cerebrospinal fluid collection when bacterial meningitis is suspected (Fiske & Bloch, 2019; World Health Organization, 2025).

Expected diagnostic and laboratory findings

  • Typical bacterial pattern: elevated opening pressure, neutrophilic pleocytosis, high protein, low glucose or low CSF:serum glucose ratio, and possible positive Gram stain/culture/PCR (Fiske & Bloch, 2019; World Health Organization, 2025).
  • Typical viral pattern: lymphocytic pleocytosis, normal glucose, and modest protein elevation. Tuberculous/fungal disease often has lymphocytes, high protein, and low glucose. Overlap occurs (Fiske & Bloch, 2019; World Health Organization, 2025).
  • Definitive diagnosis is organism detection by culture or validated molecular testing; a compatible CSF pattern may remain presumptive when prior therapy reduces yield (Fiske & Bloch, 2019; World Health Organization, 2025).

Differential diagnosis

  • Encephalitis: altered behavior, seizures, focal deficits, and brain parenchymal involvement may dominate; CSF and MRI help distinguish, but overlap is common (Fiske & Bloch, 2019; Smetana, 2012).
  • Subarachnoid hemorrhage: thunderclap headache, blood/xanthochromia, and vascular imaging rather than infectious CSF pattern (Fiske & Bloch, 2019; Smetana, 2012).
  • Migraine: recurrent stereotyped headache with normal neurologic/infectious assessment (Fiske & Bloch, 2019; Smetana, 2012).
  • Brain abscess or parameningeal infection: focal deficits or source, imaging lesion, and possibly less prominent meningeal CSF findings (Fiske & Bloch, 2019; Smetana, 2012).

Treatment and management

  • Start age-, host-, and setting-appropriate empiric intravenous antibiotics immediately when bacterial meningitis is suspected. For community-acquired disease, ceftriaxone or cefotaxime is foundational; add ampicillin or amoxicillin when Listeria risk is present, including age over 60 years, pregnancy, or immunocompromise (Fiske & Bloch, 2019; World Health Organization, 2025).
  • Give intravenous corticosteroid with the first antibiotic dose when acute bacterial meningitis is suspected in a non-epidemic setting, then discontinue it if cerebrospinal fluid findings are not consistent with bacterial meningitis (Fiske & Bloch, 2019; World Health Organization, 2025).
  • Provide airway, seizure, perfusion, intracranial-pressure, and electrolyte support. Use droplet precautions for suspected meningococcal disease and arrange prompt chemoprophylaxis for qualifying close contacts through public-health guidance (Fiske & Bloch, 2019; World Health Organization, 2025).

Additional complications and red flags

  • Antibiotic timing takes priority over complete diagnostic certainty in suspected bacterial meningitis (Fiske & Bloch, 2019; World Health Organization, 2025).

Content last reviewed:

References

Fiske, C. T., & Bloch, K. C. (2019). Infectious diseases. In G. D. Hammer & S. J. McPhee (Eds.), Pathophysiology of disease: An introduction to clinical medicine (8th ed.). McGraw-Hill Education.

Norris, T. L. (2020). Porth’s essentials of pathophysiology (5th ed.). Wolters Kluwer.

Smetana, G. W. (2012). Headache. In M. C. Henderson, L. M. Tierney, Jr., & G. W. Smetana (Eds.), The patient history: An evidence-based approach to differential diagnosis (2nd ed.). McGraw-Hill.

World Health Organization. (2025). WHO guidelines on meningitis diagnosis, treatment and care. https://www.who.int/publications/i/item/9789240108042