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CNS Infections

posted Oct 2, 2014, 8:04 AM by Lucille Torres-Deas   [ updated Oct 6, 2014, 7:14 AM ]

Created by Shirin Attarian, PGY3 during RAT rotation.

 CNS Infection Handout


 Approximately 1.2 million cases of bacterial meningitis occur annually worldwide. Meningitis is among the 10 most common infectious causes of death and is responsible for approximately 135,000 deaths throughout the world each year. Neurologic sequelae are common among survivors.

The major causes of community-acquired bacterial meningitis in adults in developed countries are Streptococcus pneumoniae, Neisseria meningitidis, and, primarily in patients over age 50 to 60 years or those who have deficiencies in cell-mediated immunity, Listeria monocytogenes. The major causes of healthcare-associated bacterial meningitis are staphylococci and aerobic gram-negative bacilli.

Viral infections of the CNS result in the clinical syndromes of aseptic meningitis or encephalitis. The true incidence of these infections is unknown.

A wide variety of different viruses can infect the CNS. A common cause of sporadic encephalitis is herpes simplex virus type 1. Other diagnostic considerations will depend on geographic location (eg, St. Louis encephalitis in North America and Japanese encephalitis in Asia) and epidemiologic clues such as exposure history (eg, bat exposure or dog bite and rabies), regional outbreaks (eg, enterovirus type 71 in Denver, Colorado), and clinical clues such as profound weakness and rash with West Nile. Uncommon causes include varicella-zoster virus, Epstein-Barr virus, HIV, and human herpes virus-6.



The presence or absence of normal brain function is the important distinguishing feature between encephalitis and meningitis. Patients with meningitis may be uncomfortable, lethargic, or distracted by headache, but their cerebral function remains normal. In encephalitis, however, abnormalities in brain function are expected, including altered mental status, motor or sensory deficits, altered behavior and personality changes, and speech or movement disorders. Seizures and postictal states can be seen with meningitis alone and should not be construed as definitive evidence of encephalitis. Other neurologic manifestations of encephalitis may include hemiparesis, flaccid paralysis, and paresthesias.


ü  Elicit a detailed sexual, travel, and exposure history (to both insects and animals).

ü  Carefully examine the patient for generalized rashes and focal neurologic findings.

ü  CSF examination of patients with suspected meningitis or encephalitis is essential for diagnosis.

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Bacterial vs viral meningitis:

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-Bacterial Meningitis:

Risk factors for bacterial meningitis:

• Terminal complement deficiencies (Neisseria)

• Military recruits, college dorms (Neisseria)

• Extremes of age (all types)

• Immunocompromise (all types)

• Splenectomy/Asplenia (all types)

• Skull fractures (Pneumococcus, Haemophilus)

• Neurosurgery (nosocomial pathogens)



·         Endemic in the United States, annual incidence of invasive meningococcal disease varies from 0.5 to 1.5 cases per 100,000.

·         Ages <1 and 16-21

·         Colonizes nasopharyngeal mucosa

·         Transmission via direct contact with large droplet respiratory secretions from patients or asymptomatic carriers

·         10%-15% of cases are fatal and 11%-19% of survivors have permanent hearing loss, mental retardation or other serious sequelae.


Listeria Meningitis:


• Age < 1 month, > age 60, pregnant F, compromised hosts (liver/kidney disease, malignancy, EtOH, etc.)

• Isolated from soft cheeses, deli meats, raw produce

• Neonatal infections from vertical transmissions

• Incubation 11-70 days

• 5th leading cause of bacterial meningitis, highest mortality (15-30%)


Pneumococcal Meningitis/Invasive Pneumococcus:


• Affects infants & young children, AA, Native Americans, elderly, compromised hosts (AIDS)

• Most common cause of bacterial meningitis (58% of cases)

• Mortality 18-26%; 14% of hospitalized adults

• Spread by infected respiratory secretions

• Incubation 1-3 days

• Associations:

– Pneumonia (25%)

– Otitis media/mastoiditis (30%)

– Sinusitis (10-15%)

– Endocarditis (<5%)

– Head trauma with CSF leak (10%)


Haemophilus influenzae type b Meningitis:


• Pleomorphic gram negative coccobacillus (encapsulated or non-encapsulated)

• Since Hib vaccine (1990), nontypeable H. influenzae now causes the majority of invasive disease

• Basilar skull fracture with disruption of sinuses and CSF leak

• Concurrent otitis media or sinusitis

• Asplenia or SS disease

• Other immune deficiency, EtOH, DM


Management algorithm for adults with suspected bacterial meningitis:

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 Recommendations for antimicrobial therapy:

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Duration of antimicrobial therapy:

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Treatment of pneumococcal meningitis

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Adjunctive Steroids – Expert Panel Recommendation:

• For suspected Pneumococcal meningitis:

– Dexamethasone 0.15mg/kg q6h x 2-4 days starting just before or concomitant with first dose of Abx

– Only continue for confirmed Pneumococcus

• Unlikely to improve outcome in patients who have already received Abx

• Data inadequate for steroids in adults with meningitis due to other bacterial pathogens


Isolation precautions: refer to attachment for image

HSV Meningoencephalitis

Herpes encephalitis is the most common cause of fatal sporadic encephalitis in the United States and involves all age groups. In nearly all cases of herpes encephalitis beyond the neonatal period, the etiologic agent is herpes simplex virus type 1 (HSV-1). In neonates, herpes encephalitis may be caused by either HSV-1 or HSV-2. The clinical syndrome is often characterized by the rapid onset of fever, headache, seizures, focal neurologic signs, and impaired consciousness.

• Bimodal distribution (< 20y and > 50y)

• Immune-mediated tissue injury/necrosis, particularly in temporal lobes

• > 90% of patients with have fever + Acute onset focal neurologic signs:

– Altered mentation and level of consciousness

– Cranial nerve deficits

– Hemiparesis or ataxia

– Dysphasia or aphasia

– Focal seizures

• Focal EEG findings in >80%

• Characteristic MRI enhancement in medial temporal lobes


Diagnosis: Lumbar puncture for cerebrospinal fluid analysis and polymerase chain reaction (PCR) testing for HSV in any patient with encephalitis.

-Brain MRI is recommended to assess signs of temporal lobe involvement, which would support the diagnosis. Absence of this finding does not alter decisions regarding empiric therapy. Brain MRI would also eliminate other alternative causes of mental status changes, such as brain abscess.

Treatment: Empiric treatment with Acyclovir (10 mg/kg IV every 8 hours)  is recommended if HSV encephalitis is suspected. Treatment duration is 14 to 21 days.

-Thanks to Dr. Priya Nori for sharing her slides with me.



-Tunkel A R et al. Clin Infect Dis. 2004;39:1267-1284


-Harrison’s Principles of Internal Medicine