9.1 Bacterial, Viral & Fungal Meningitis

Bacterial, Viral, and Fungal Meningitis

Meningitis is the inflammation of the meninges, the protective membranes surrounding the brain and spinal cord, specifically the pia mater and the arachnoid mater, as well as the subarachnoid space containing cerebrospinal fluid (CSF). Understanding the nuances between bacterial, viral, and fungal etiologies is critical for the neuroscience nurse, as bacterial meningitis constitutes a life-threatening neurological emergency requiring immediate and aggressive intervention, whereas viral meningitis generally follows a self-limiting course.

Bacterial Meningitis

Bacterial meningitis is a rapidly progressive and potentially fatal infection. The most common causative pathogens in adults include Streptococcus pneumoniae (pneumococcus) and Neisseria meningitidis (meningococcus). Other pathogens, such as Listeria monocytogenes, are more frequently seen in neonates, the elderly, and immunocompromised individuals. Pathogens typically access the CNS via hematogenous spread from a primary infection site (e.g., respiratory tract) or through contiguous spread from adjacent structures (e.g., otitis media, sinusitis), or via direct inoculation (e.g., skull fractures, neurosurgical procedures).

Clinical Manifestations

The classic triad of bacterial meningitis includes headache, fever, and nuchal rigidity (stiff neck). However, all three are present in only about 44% of adults. Patients often exhibit altered mental status ranging from confusion to coma, photophobia, and signs of meningeal irritation.

Two key physical examination findings point to meningeal irritation:

• Kernig's sign: Resistance and pain with extension of the patient's leg from a flexed position.
• Brudzinski's sign: Involuntary flexion of the hips and knees when the patient's neck is passively flexed.

In cases of N. meningitidis, patients may present with a characteristic petechial or purpuric rash, indicative of meningococcemia, which can rapidly progress to disseminated intravascular coagulation (DIC) and septic shock (Waterhouse-Friderichsen syndrome).

Diagnostics and CSF Findings

Diagnosis hinges on lumbar puncture (LP) and CSF analysis. A CT scan of the head should precede LP in patients with papilledema, focal neurological deficits, new-onset seizures, severely altered level of consciousness, or an immunocompromised state to rule out a space-occupying lesion and prevent brain herniation.

Classic Bacterial CSF Findings:

• Opening pressure: Elevated (often > 20 cm H2O)
• WBC count: Markedly elevated (> 1000/mcL), predominantly polymorphonuclear leukocytes (PMNs) or neutrophils.
• Protein: Elevated (> 100 mg/dL), reflecting increased capillary permeability and breakdown of the blood-brain barrier.
• Glucose: Decreased (< 40 mg/dL, or CSF-to-serum glucose ratio < 0.4), as bacteria and leukocytes consume glucose.
• Gram stain and culture: Positive for the offending organism in the majority of untreated cases.

Medical Management and Nursing Interventions

Time is brain. Treatment must not be delayed for diagnostic procedures if bacterial meningitis is strongly suspected. Empiric therapy typically involves vancomycin (to cover resistant S. pneumoniae) plus a third-generation cephalosporin like ceftriaxone or cefotaxime (to cover N. meningitidis and susceptible S. pneumoniae). Ampicillin is added for adults over 50 or those with impaired cellular immunity to cover Listeria.

Corticosteroids, specifically dexamethasone, are strongly recommended. They should be administered 10 to 20 minutes before or concurrently with the first dose of antibiotics. Dexamethasone attenuates the inflammatory response in the subarachnoid space triggered by bacterial lysis, significantly reducing the risk of neurological complications, most notably sensorineural hearing loss.

Isolation Precautions: The nurse must immediately initiate droplet precautions for patients with suspected bacterial meningitis, particularly for N. meningitidis and H. influenzae, continuing until the patient has received 24 hours of appropriate and effective antibiotic therapy.

Viral (Aseptic) Meningitis

Viral meningitis is the most common form of meningitis. Enteroviruses (e.g., coxsackievirus, echovirus) are responsible for the vast majority of cases. Other culprits include Herpes Simplex Virus (HSV), HIV, and arthropod-borne viruses (arboviruses).

The clinical presentation is similar to bacterial meningitis—fever, headache, photophobia, and stiff neck—but generally less severe. Patients rarely exhibit profound alterations in consciousness or focal neurological deficits unless there is concurrent encephalitis.

Classic Viral CSF Findings:

• WBC count: Mild to moderate elevation (10-1000/mcL), predominantly lymphocytes.
• Protein: Normal to mildly elevated (< 100 mg/dL).
• Glucose: Usually normal (> 45 mg/dL).
• Gram stain: Negative.

Management is primarily supportive, emphasizing rest, hydration, antipyretics, and analgesics. If HSV is suspected, antiviral therapy (acyclovir) is initiated pending PCR results. Most patients recover completely within 7 to 10 days.

Fungal Meningitis

Fungal meningitis is indolent and typically affects immunocompromised hosts, such as patients with advanced HIV/AIDS, organ transplant recipients, or those on chronic immunosuppressive therapy. Cryptococcus neoformans is a frequent cause, often acquired through inhalation of spores from bird droppings.

Symptoms develop insidiously over weeks to months. The CSF profile typically shows a lymphocytic pleocytosis, elevated protein, and low glucose. Diagnosis is confirmed via India ink stain, fungal culture, or detection of cryptococcal antigen in the CSF.

Treatment is prolonged and complex, often involving an induction phase with intravenous amphotericin B and flucytosine, followed by a consolidation and maintenance phase with oral fluconazole. Nursing care focuses on monitoring for severe side effects of antifungal agents, particularly the nephrotoxicity and electrolyte imbalances associated with amphotericin B, and managing intracranial pressure, which can be profoundly elevated in cryptococcal meningitis, often necessitating serial lumbar punctures or the placement of a lumbar drain or ventriculoperitoneal shunt.

In all cases of meningitis, the neuroscience nurse's vigilance in monitoring neurological status, maintaining appropriate isolation, managing fever to reduce cerebral metabolic demands, and mitigating increased intracranial pressure remains the cornerstone of comprehensive care.