CNS infections-part 2

• Many bacteria can cause meningitis.

Age of onset Common Less common
Neonate Gram-negative bacilli (Escherichia coli, Proteus etc.)
Group B streptococci Listeria monocytogenes
Pre-school child Haemophilus influenzae Mycobacterium tuberculosis
Neisseria meningitidis
Streptococcus pneumoniae
Older child and adult Neisseria meningitidis
Streptococcus pneumoniae Listeria monocytogenes
Mycobacterium tuberculosis
staphylococcus aureus (skull fracture)
Haemophilus influenzae
elderly Streptococcus pneumoniae
Neisseria meningitidis
Gram-negative bacilli Listeria monocytogenes

• Streptococcus pneumoniae is the most common cause of bacterial meningitis, followed by Neisseria meningitidis.
• The meningococcus and other common causes of meningitis are normal commensals of the upper respiratory tract. New and potentially pathogenic strains are acquired by the air-borne route, but close contact is necessary.
• The organism invades through the nasopharynx, producing septicemia that is usually associated with pyogenic meningitis.
• In pneumococcal and Haemophilus infections there may be an associated otitis media. Pneumococcal meningitis may be associated with pneumonia and occurs especially in older patients and alcoholics, as well as those with asplenia.
• Listeria monocytogenes can cause meningitis in the immunosuppressed, diabetics, alcoholics, pregnant women, as well as in the extremes of age.

Clinical features
• Headache, drowsiness, fever and neck stiffness are the usual presenting features.
• In severe bacterial meningitis the patient may be comatose and later there may be focal neurological signs.
• Meningococcal meningitis may be associated with a purpuric rash.

Investigations:

Symptoms& signs of meningitis
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Blood culture, throat swab
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Empirical antibiotics
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Brain CT scan to exclude space occupying lesions
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Lumbar puncture

• In bacterial meningitis the CSF is cloudy (turbid) due to the presence of many neutrophils, so called septic meningitis.
• Gram stain and culture of CSF may allow identification of the organism.
• Polymerase chain reaction (PCR) techniques can be used on both blood and CSF to identify bacterial DNA.





CSF character Normal Viral Pyogenic Tuberculosis
Appearance Crystal-clear Clear/turbid Turbid/purulent Turbid/viscous
Mononuclear cells
(Lymphocyte) < 5/ mm3 10-100/ mm3 < 50 mm3 100-300 mm3
Polymorph cells
(neutrophil) Nil Nil 200-300/mm3 0-200/mm3
Protein 0.2-0.4 g/L 0.4-0.8 g/L 0.5-2.0 g/L 0.5-3.0 g/L
Glucose ? 60% blood glucose ? 60% blood glucose < 60% blood glucose < 60% blood glucose

Management:
• If bacterial meningitis is suspected, parenteral (i.v.) empirical antibiotics should be given immediately before the cause of meningitis is known.

Antibiotics Used in Empirical Therapy of Bacterial Meningitis

Indication Antibiotic
Preterm infants to infants <1 month Ampicillin + cefotaxime
Infants 1–3 mos Ampicillin + cefotaxime or ceftriaxone
Immunocompetent children >3 mos and adults <55 Cefotaxime or ceftriaxone + vancomycin
Adults >55 and adults of any age with alcoholism or other debilitating illnesses Ampicillin + cefotaxime or ceftriaxone + vancomycin
Hospital-acquired meningitis, posttraumatic or postneurosurgery meningitis, neutropenic patients, or patients with impaired cell-mediated immunity Ampicillin + ceftazidime + vancomycin
Patients with a clear history of anaphylaxis to
?-lactams Chloramphenicol 25 mg/kg i.v. 6-hourly
plus
Vancomycin 1 g i.v. 12-hourly

• The antibiotic regimen may be modified after identifying the infecting organism.
• Duration of antibiotic treatment depends on the infecting organism, but usually for 2-3 weeks.
• Adjunctive corticosteroid therapy is useful in both children and adults. Dexamethasone (10 mg intravenously) should be administered 20 min before or concurrent with the first dose of antibiotics and the same dose is repeated every 6 h for 4 days.
• Household and other close contacts of patients with meningococcal infections, especially children, should be given 2 days of oral rifampicin (age 3-12 months 5 mg/kg 12-hourly, > 1 year 10 mg/kg 12-hourly, and adults 600 mg 12-hourly). In adults, a single dose of 500 mg of ciprofloxacin is an alternative.

Prognosis:
In general, the risk of death from bacterial meningitis increases with
(1) decreased level of consciousness on admission,
(2) Onset of seizures within 24 h of admission,
(3) Signs of increased ICP
(4) Young age (infancy) and age >50
(5) Delay in the initiation of treatment.
(6)Decreased CSF glucose concentration (<40 mg/dL)
(7) Markedly increased CSF protein concentration (>300 mg/dL)