Bacterial Meningitis

Question 1

Definition of bacterial meningitis

Answer 1

Inflammation of the meninges due to a bacterial infection

Question 2

Epidemiology of bacterial meningitis

Answer 2

Incidence of bacterial meningitis in Western countries is 0.7 to 0.9 per 100,000. Incidence in African countries is 10 to 40 per 100,00 persons per year.

Question 3

Risk factors for bacterial meningitis

Answer 3

Strong:
Advanced age
Crowding 
Exposure to pathogens (within household or close contact) Ask about source of infection such as otitis media or contact with a person who has had suspected sepsis
Immunocompromising consitions 
Cranial anatomical defects/ventriculoperitoneal shunt 
Cochlear implant
Sickle cell disease 

Weak:
Contiguous infection: sinusitis, pneumonia, mastoiditis + otitis media

Question 4

Aetiology of bacterial meningitis

Answer 4

1. Strep pneumoniae = most common cause. Introduction of pneumococcal conjugate vaccine has decreased incidence significantly.
2. Listeria monocytogenes = common cause of bacterial meningitis in patients using immunosuppresive drugs, people who misuse alcohol + patients with diabetes mellitus
3. Zoonotic causesof bacterial meningitis is rare but important to consider.
   Strep suis = assoc. w raw pork meat
   Caprocytophagia canimorsus = assoc. w dogs
   Campylobacter fetus = cattle
   Strep equi = horses

Question 5

Pathophysiology of bacterial meningitis

Answer 5

Bacteria reach CNS by haemoptysis spread (most common route) or by direct extension from a contiguous site –> bacteria multiples quickly once they have entered the subarachnoid space. Bacterial components in CSF induce production of various inflammatory mediators –> enhances influx of leukocytes into CSF –> leads to cerebral oedema and elevated ICP which contribute to neurological damage and even death

Question 6

Hx and Exam of bacterial meningitis

Answer 6

1. Headache
2. Neck stiffness
3. Fever
4. Altered mental status
5. Vomiting
6. Confusion
7. Photophobia
8. Seizures
9. Risk factors

Other diagnostic factors:

1. Focal neurological signs
   - dilated non-reactive pupil
   - abnormalities of ocular motility
   - abnormal visual fields
   - gaze palsy, arm or leg drift
   - suggests an increase in ICP
2. Abnormal eye movement - cranial nerve palsy (III,IV,VI), increase in ICP
3. Facial nerve palsy CNVII may be damaged due to increased ICP and inflammation
4. CN VIII may be damaged due to increased ICP and inflammation
5. Rash - petechial or purpuric
6. Papilloedema: signs of increased ICP. Enlarged blind spot may be present when examining visual fields
7. Kernig’s sign: pain in lower back or back of thigh on extension of knee when hip flexed to a right angle
8. Brudzinski’s sign: forced flexion of neck elicits a reflex flexion of this hips. Alternative sign is passive flexion of the leg on one side causing contralateral flexion of the opposite leg.

Question 7

Investigations of bacterial meningitis

Answer 7

1. Blood culture = positive blood culture
2. Serum pneumococcal + meningococcal PCR = positive for specific antigen
3. Serum urea, creatinine + electrolytes = acidosis, hypokalemia, hypocalcemia, hypomagnesemia, hyponatremia may indicate tuberculosis meningitis
4. Blood glucose = hypoglycemia or hyperglycemia
5. FBC: leukocytosis, anaemia, thrombocytopenia
6. VBG = shock may be indicated by a lactate concentration of > 4mmol/L
7. LFTs = raised LFTs
8. Serum HIV = +ve (may be -ve in seroconversion illness)
9. Coagulation screen = evidence of DIC, increased PT, increased fibrin, degradation products of D-dimer, low fibrinogen or antithrombin levels
10. Serum procalcitonin = elevated or normal
11. Serum CRP = high CRP
12. CSF protein = usually elevated
13. CSF lactate = > 35mg/dL suggests bacterial or viral cause
14. CSF glucose = if conc. is <12,5mmol/L (<45mg/dL) or <40% of simultaneously measured serum glucose in bacterial meningitis
15. CSF microscopy = gram +ve or gram -ve
16. CSF cell count = polymorphnuclear pleocytosis w WBC > 1.0x 10^9 in untreated bacterial meningitis
17. CSF PCR for pneumococcus = may be positive

Question 8

Management of Bacterial meningitis

Answer 8

Initial Mx:
<60 years + immunocompotent:
Supportive care, corticosteroid (dexamethasone), empiric abx: ceftriaxone/cefotaxime 2nd line: chloramphenicol. Consider abx cover for penicillin resistant pneumoocci consider tx for unusual pathogens.

> 60 years or immunocompetent:
Supportive care, corticosteroid (dexamethasone), empiric abx: ceftriaxone/cefotaxime 2nd line: chloramphenicol PLUS abx cover for listeria monocytogenes: amoxicillin or trimethoprim/sulfamethoxazole
Consider abx cover for penicillin resistant pneumoocci consider tx for unusual pathogens.

CONFIRMED bacterial meningitis:
1. B. meningitis caused by haemophilus influenzae
1st line: 10 day course of ceftriaxone or cefotaxime
2nd line: moxifloxacin
PLUS supportive care PLUS corticosteroid: dexamethasone

2. B. meningitis caused by enterobacteriae
   Abx: 1st line: 21 day course of ceftriaxone/cefotaxime/chloramphenicol
   2nd line: meropenem PLUS supportive care
3. B. meningitis caused by strep pneumoniae
   1st line: ceftriaxone/cefotaxime/benzylpenicillin/ chloramphenicol PLUS supportive care and corticosteroid (dexamethasone)
4. B. meningitis caused by Listeria monocytogenes
   1st line: amoxicillin
   2nd line: trimethoprim/sulfamethoxazole
   PLUS supportive care

5.B. meningitis caused by staph aureus
Non-MRSA penicillin sensitive:
1st line: Flucloxacillin/flucloxacillin-flucloxicillin AND rifampicin/fosformycin
2nd line: MRSA-vancomycin sensitive:
vancomycin and rifampicin OR MRSA vancomycin-resistant or contraindicated: Linezolid OR MRSA-vancomycin resistant: Linezolid and rifampicin PLUS supportive care

6. B. meningitis caused by mycobacterium tuberculosis
   1st line: Abx
7. Neisseris meningitis: see meningococcal disease
8. Unconfirmed clinically suspected bacterial meningitis
   PLUS continue empiric abx, supportive care, corticosteroid: dexamethasone