Acute Bacterial Meningitis

Definition

• Bacterial infection of the subarachnoid space

Microbiology in Adult Meningitis

Etiology

(30-60%)

Most common cause in adults.

Look for distant infection (eg, Osier's triad meningitis.

pneumonia, endocarditis). Drug-resistant S. pneumoniae (DRSP):

40% PCN-resistant (20% intermed.; 15-20% high) • 10% 3rd gen. ceph.-resistant (5% intermed.; < 5% high) even intermed. resistance problematic for Rx of meningitis

N. meningitidis

(10-35%)

Primarily in children and young adults; may be associated with petechiae or purpura. Deficiencies in terminal complement predispose to recurrent meningococcemia & rarely, meningitis.

H. influenzae

(<5%)

1 incidence in children because of H. influenzae type b vaccine. Look for predisposing factors in adults (eg. CSF leak, recent neurosurgical procedure, trauma, mastoiditis).

L. monocytogenes (5-10%)

Seen in elderly, alcoholics, or patients with malignancy, immunosuppression, or iron overload. Outbreaks associated with contaminated milk, cheese, coleslaw, raw vegetables. Despite name, often associated with poly-predominant pleocytosis.

GNRs (1-10%)

Usually nosocomial or postprocedure or in elderly or i mmu nosuppressed.

Staphylococci (5%)

Seen with indwelling CSF shunt (S. epidermidis) or following neurosurgery or head trauma (S. aureus).

Mixed infection

Suspect parameningeal focus or CSF leak.

Clinical manifestations (NEjm 2006:354:14)

• Headache (87%). stiff neck (83%). and photosensitivity

• 2 of 4 (fever. HA. stiff neck, a MS) present in 95%

• Presentation may be atypical in elderly and immunocompromised, with primarily lethargy and confusion, and no fever

Physical exam

• Nuchal rigidity (Se 30%). Kernig's sign (Pt supine, hip flexed at 90". knee flexed at

90°; ® if passive extension of knee results in resistance). Brudzinski's sign (Pt supine and limbs supine: - if passive neck flexion - involuntary hip and/or knee flexion) nb. Kernig's and Brudzinski's signs * in only 5% of Pts (OD 200245:46)

• • Focal neuro findings ( 30%: hemiparesis. aphasia, visual field cuts. CN palsies)

• • Funduscopic findings: papilledema, absent venous pulsations

• • Rash: maculopapular, petechial, or purpuric Diagnostic studies

• Blood cultures

• Consider head CT to r/o mass effect before LP if presence of high-risk feature (age

60 y. immunocompromised, h/o CNS disease, new onset seizure. A MS. focal neuro findings): absence of all these has NPV 97%; however, should be noted that in Pts wI mass effect, herniation may occur even w/o LP and may not occur even w/ LP (nejm 2001:345:1727)

• Lumbar puncture <n£}M 2006:355 e12): CSF Gram stain has 60-90% Se: cx has 70-85% Se

CSF Findings in Meningitis

Condition

Appearance

Pressure (cm)

WBC/mm1 Prtdom type

Glc (mg/dl)

(mg/dl)

Normal

Clear

9-18

0-5 lymphs

50-75

15-«

Bacterial

Cloudy

18-30

100-10.000

•45

100-1000

poys

TB

Cloudy

18-30

-500

<45

100-200

lymphs

Fungal

Cloudy

18-30

■300 fjmphs

<■15

40-300

Aseptic

Clear

9-18

■ 300

50-100

50-100

potys fymphs

• Additional CSF studies depending on clinical suspicion: acid-fast smear and ex. India ink preparation, cryptococcal antigen, fungal ex. PCR (eg. of HSV. VZV. enteroviral). cytology

Treatment of Meningitis

Clinical scenario Normal adult

Empiric treatment guidelines*

Ceftriaxone 2 g IV q12h + Vancomycin 1 g IV q12h

(nb. Cftx in case PCN-resistant 5. pneumo; Vanco, which has poorer CSF penetration, in case Cftx-resistant S. Pneumo) If 50 y old: * Ampicillin 2 g IV q4h for listeria TMP/SMX * vancomycin if ^-lactam allergic

Immunocompromised

Ampicillin • ceftazidime ■ vancomycin • acyclovir

CSF shunts, recent neurosurgery, or head trauma

Vancomycin ■ ceftazidime

Empiric antibiotics should be started as soon as possible. If concerned about * ICP, obtain BCx -» start empiric abx -. obtain head CT - LP (if not contraindicated); yield of CSF fluid unlikely to be changed if obtained w/in 4h of initiation of abx.

Corticosteroids: Dexamethasone 10 mg IV q6h ■ 4 d -. : neuro disability & mort. by 50% w / 5. pneumo & GCS 8-11. Must start before or w/1 st dose of abx inejm 200U47 1S49)

Prophylaxis: rifampin (600 mg PO bid < 2 d) or ciprofloxacin (500 mg PO • 1) or ceftriaxone (250 mg IM x 1) for close contacts of Pi w/ meningococcal meningitis.

•When possible, organism-directed Rx. guided by suscept. or local patterns of drug resistance should be used.

•When possible, organism-directed Rx. guided by suscept. or local patterns of drug resistance should be used.

Prognosis

• For community-acquired S. pneumo more 19-37%; 30% have long-term neuro sequelae

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