Infections of the Central Nervous System

📋 Key Information Summary

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CNS infections are neurological emergencies — empirical antibiotics (and aciclovir for suspected encephalitis) must not be delayed for imaging or lumbar puncture if there is clinical deterioration or contraindications to immediate LP.
Bacterial meningitis in Australian adults is most commonly caused by Neisseria meningitidis and Streptococcus pneumoniae; in neonates, Group B Streptococcus, Listeria monocytogenes and E. coli predominate.
Classic CSF findings in bacterial meningitis: turbid appearance, raised opening pressure (>25 cmH₂O), WBC >1000/µL (neutrophil predominant), low glucose (<2.2 mmol/L or CSF:serum ratio <0.4), raised protein (>1 g/L).
Empirical adult treatment for bacterial meningitis: IV ceftriaxone 2 g Q12H + IV dexamethasone 0.15 mg/kg Q6H for 4 days (started before or with the first antibiotic dose). Add IV ampicillin 2 g Q4H if Listeria risk (>50 years, immunocompromised, pregnancy).
Dexamethasone reduces mortality and neurological sequelae in pneumococcal meningitis — administer before or with the first dose of antibiotics and continue for 4 days.
Viral meningitis is most commonly enteroviral; CSF shows lymphocytic pleocytosis, normal glucose, mildly raised protein. It is usually self-limiting and managed with supportive care.
HSV encephalitis is the most important treatable cause of encephalitis — start IV aciclovir 10 mg/kg Q8H immediately on clinical suspicion; do not wait for MRI or PCR results. A negative CSF HSV PCR within 72 hours of onset does not exclude diagnosis.
Autoimmune encephalitis (especially anti-NMDA receptor) should be considered when infectious causes are negative — presents with psychiatric symptoms, seizures, movement disorders, and autonomic instability. First-line immunotherapy: IV methylprednisolone + IV immunoglobulin or plasma exchange.
Brain abscess presents with progressive headache, focal neurological deficit, and fever; CT with contrast or MRI is the imaging modality of choice. Empirical therapy: IV ceftriaxone + IV metronidazole ± vancomycin if MRSA risk.
CT before LP: required if immunocompromised, history of CNS disease, new-onset seizures, papilloedema, GCS <12, focal neurological deficit, or age ≥65 years. Do not delay antibiotics while awaiting CT or LP.
Public health notifications: bacterial meningitis (N. meningitidis, Haemophilus influenzae) is notifiable in all Australian states/territories — notify the local public health unit and arrange chemoprophylaxis for close contacts.
Aboriginal and Torres Strait Islander populations have significantly higher rates of invasive meningococcal and pneumococcal disease; lower vaccination coverage, remote geography, and delayed presentation contribute to worse outcomes.

Introduction & Australian Epidemiology

Infections of the central nervous system (CNS) encompass a spectrum of conditions including meningitis, encephalitis, and brain abscess. These represent some of the most time-critical diagnoses in medicine, where delays in treatment of even a few hours can result in death or devastating neurological disability. The approach to CNS infections in Australian practice is shaped by the country's unique epidemiology, including higher burdens of disease in Aboriginal and Torres Strait Islander populations, geographically remote communities with limited specialist access, and distinct antimicrobial resistance patterns.

Key Australian epidemiological data:

Invasive meningococcal disease: approximately 200–350 notifications per year nationally, with serogroup B now predominant following the success of the serogroup C conjugate vaccine programme. Peak incidence is in children <5 years and young adults 15–24 years (Australian Government Department of Health, National Notifiable Diseases Surveillance System).
S. pneumoniae remains the leading cause of bacterial meningitis in adults in Australia, with case fatality rates of 15–25%. The introduction of conjugate pneumococcal vaccines into the National Immunisation Programme (NIP) has reduced paediatric cases significantly.
Viral meningitis accounts for the majority of meningitis presentations in Australia, with enteroviruses being the predominant aetiology, peaking in late summer and autumn.
HSV encephalitis has an incidence of approximately 1–2 per million population per year in Australia, with significant morbidity even with antiviral treatment.
Brain abscess is relatively uncommon (2–4 per 100,000 per year) but carries a mortality of 10–20% even with modern treatment.
Aboriginal and Torres Strait Islander Australians experience rates of invasive pneumococcal disease 5–8 times higher than non-Indigenous Australians and invasive meningococcal disease rates approximately 3–4 times higher, particularly in remote Northern Territory and Western Australian communities (AIHW, RHDAustralia).

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Time-critical intervention: In suspected bacterial meningitis or encephalitis, empirical treatment must be administered within 30 minutes of clinical suspicion. Do not delay treatment for CT or lumbar puncture when these cannot be performed promptly. Administer IV dexamethasone and ceftriaxone (± ampicillin ± aciclovir) immediately and arrange urgent LP once the patient is stabilised.

Bacterial Meningitis

Organisms by Age Group and Risk Factors

Population	Common Organisms	Risk Factors
Neonates (<1 month)	Group B Streptococcus (GBS), E. coli (K1 capsule), Listeria monocytogenes	Prematurity, maternal GBS colonisation, chorioamnionitis
Infants (1–3 months)	GBS, E. coli, Listeria, S. pneumoniae, N. meningitidis	Complement deficiency, asplenia
Children (3 months – 18 years)	N. meningitidis (B > W), S. pneumoniae	Complement deficiency, cochlear implants, CSF leaks
Adults (18–50 years)	S. pneumoniae, N. meningitidis	Sinusitis, otitis media, mastoiditis, alcoholism, CSF leak
Older adults (>50 years)	S. pneumoniae, Listeria monocytogenes, Gram-negative bacilli	Immunosuppression, diabetes, alcoholism, neurosurgery
Immunocompromised	Listeria, Gram-negatives, S. pneumoniae, Cryptococcus neoformans	HIV/AIDS, transplant, corticosteroids, biologics
Post-neurosurgery / VP shunt	Staphylococci (coagulase-negative, S. aureus), Gram-negatives, Propionibacterium	CSF shunts, drains, craniotomy

CSF Findings — Bacterial vs Viral vs Fungal

Parameter	Bacterial Meningitis	Viral Meningitis	Fungal / TB
Appearance	Turbid / purulent	Clear	Clear to slightly turbid
Opening pressure	>25 cmH₂O (often >30)	Normal to mildly raised	Often raised (>25)
WCC (cells/µL)	>1000 (neutrophil predominant)	10–500 (lymphocyte predominant)	100–500 (lymphocyte predominant, mixed in TB)
Glucose	Low (<2.2 mmol/L); CSF:serum <0.4	Normal (≥2.2 mmol/L); CSF:serum >0.6	Low in TB and cryptococcal; CSF:serum <0.4
Protein	Raised (>1 g/L, often >3)	Mildly raised (0.5–1.0 g/L)	Raised (>1 g/L in TB)
Gram stain	Positive in 60–90%	Negative	AFB positive in ~30% TB; India ink positive in cryptococcal
Latex agglutination / PCR	Positive for bacterial antigens / PCR	Enterovirus PCR positive in >85%	Cryptococcal antigen; TB PCR (GeneXpert MTB/RIF)

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Partially treated meningitis: Prior antibiotic use can alter CSF findings, converting the picture from classic bacterial to a "partially treated" pattern with lower WCC, less neutrophil predominance, and normal glucose. If clinical suspicion remains high, continue empirical treatment and use CSF PCR (e.g., multiplex PCR) to identify the causative organism.

Empirical Treatment — Bacterial Meningitis

Adults (18–50 years, community-acquired, no risk factors for resistant organisms)

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Ceftriaxone

Rocephin® · Cephalosporin (3rd generation)

Adult dose 2 g IV Q12H (some guidelines Q24H — use Q12H for meningitis)

Paediatric dose 100 mg/kg/day IV in 1–2 divided doses (max 4 g/day)

Duration 7–10 days (meningococcal 7 days; pneumococcal 10–14 days)

Renal adjustment No adjustment required (biliary excretion predominant)

PBS status ✔ PBS General Benefit

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Dexamethasone

Various · Corticosteroid (adjunctive)

Adult dose 0.15 mg/kg IV Q6H for 4 days (commence before or with first antibiotic dose)

Paediatric dose 0.15 mg/kg IV Q6H for 4 days (infants and children ≥2 months)

Duration 4 days (discontinue if non-pneumococcal aetiology confirmed)

Renal adjustment No adjustment required

PBS status ✔ PBS General Benefit

Older Adults (>50 years) or Immunocompromised — Add Listeria Cover

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Ampicillin

Various · Penicillin (aminopenicillin)

Adult dose 2 g IV Q4H (in addition to ceftriaxone + dexamethasone)

Paediatric dose 75–100 mg/kg/day IV divided Q6H (max 12 g/day)

Duration 21 days for Listeria meningitis

Renal adjustment Reduce dose if eGFR <30 mL/min — extend interval to Q6–8H

PBS status ✔ PBS General Benefit

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Listeria risk groups (add ampicillin): Age >50 years, pregnancy, immunosuppression (corticosteroids, transplant, biologics), chronic liver disease, diabetes mellitus, alcohol use disorder, HIV/AIDS. If penicillin allergy (anaphylaxis), use IV trimethoprim-sulfamethoxazole 5/25 mg/kg Q6–8H instead.

Post-Neurosurgical / VP Shunt / Healthcare-Associated Meningitis

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Vancomycin

Various · Glycopeptide

Adult dose 25–30 mg/kg IV loading dose (max 2 g), then 15–20 mg/kg Q8–12H; target trough 15–20 mg/L

Duration 10–14 days (longer for retained hardware)

Renal adjustment Dose reduce per AUC-guided monitoring (target AUC/MIC 400–600)

PBS status ✔ PBS General Benefit

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Cefepime

Maxipime® · Cephalosporin (4th generation)

Adult dose 2 g IV Q8H (covers Pseudomonas and Enterobacter spp.)

Duration 10–14 days

Renal adjustment Reduce to 1 g Q8H if eGFR 30–60; 1 g Q12H if eGFR 11–29

PBS status Authority Required

Pathogen-Specific Directed Therapy

Organism	First-Line	Duration	Notes
N. meningitidis	Ceftriaxone 2 g IV Q12H	7 days	Penicillin G 4 MU IV Q4H if confirmed sensitive. Notify public health. Contact prophylaxis: ciprofloxacin 500 mg PO single dose or ceftriaxone 250 mg IM single dose.
S. pneumoniae	Ceftriaxone 2 g IV Q12H	10–14 days	Add vancomycin if MIC ≥1 mg/L or ceftriaxone resistance is suspected. Adjunctive dexamethasone strongly recommended.
Listeria monocytogenes	Ampicillin 2 g IV Q4H (or penicillin G 4 MU IV Q4H)	21 days	Cephalosporins have no Listeria activity. Add gentamicin 5–7 mg/kg IV OD for synergy in severe disease.
GBS (neonatal)	Penicillin G 50,000 U/kg IV Q8H (neonate) + gentamicin for synergy	14–21 days	Vary by gestational age — consult neonatal dosing guidelines.
Haemophilus influenzae	Ceftriaxone 2 g IV Q12H	7–10 days	Notify public health. Contact prophylaxis for household contacts: rifampicin 600 mg (adults) or 10 mg/kg (children) PO BD for 4 days.
S. aureus (MRSA)	Vancomycin 15–20 mg/kg Q8–12H (trough 15–20 mg/L)	14 days minimum	Consider rifampicin 600 mg PO/IV BD as adjunct for retained hardware. CA-MRSA increasingly relevant in remote NT/Qld communities.

Chemoprophylaxis for Close Contacts

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N. meningitidis contacts: Ciprofloxacin 500 mg PO single dose (adults) OR ceftriaxone 250 mg IM single dose (adults) / 125 mg IM single dose (children <12 years). Must be given within 24 hours of case identification. Rifampicin 600 mg PO BD for 2 days is an alternative but is not preferred due to interactions and compliance.

Viral Meningitis

Viral meningitis is the most common form of meningitis in Australia, accounting for the majority of cases presenting to emergency departments. It is generally self-limiting, with excellent prognosis in immunocompetent individuals, but requires careful differentiation from bacterial meningitis and early encephalitis.

Aetiology

Enteroviruses (coxsackievirus, echovirus, enterovirus 71, EV-D68) — cause >85% of viral meningitis cases; peak in late summer and autumn in Australia.
Herpes simplex virus type 2 (HSV-2) — the most common viral cause of recurrent lymphocytic meningitis (Mollaret meningitis); accounts for approximately 5% of cases.
Varicella zoster virus (VZV) — can cause meningitis with or without concurrent shingles.
HIV — may present as acute meningitis seroconversion illness; always consider and test.
Arboviruses — Murray Valley encephalitis virus, Kunjin/West Nile virus, Ross River virus, and Japanese encephalitis virus (emerging in northern Australia) can cause meningitis or encephalitis.
Mumps — now rare in Australia due to MMR vaccination, but still seen in under-vaccinated populations.

Clinical Features

Acute onset headache, fever, photophobia, neck stiffness, nausea and vomiting.
No focal neurological deficits (distinguishes from encephalitis).
No altered level of consciousness (if present, consider encephalitis or bacterial meningitis).
May have concurrent symptoms of viral illness: rash (enteroviral), pharyngitis, diarrhoea, myalgia.

CSF Findings

Clear CSF, normal opening pressure (or mildly raised).
WCC 10–500 cells/µL, lymphocyte predominant (early may be neutrophil predominant — repeat LP in 8–12 hours if initial CSF was neutrophil-predominant).
Normal glucose (CSF:serum ratio >0.6).
Protein mildly raised (0.5–1.0 g/L).
Enterovirus PCR positive in ≥85% of CSF samples during peak season.

Management

ℹ️

Key principle: Viral meningitis is managed supportively. However, always treat empirically for bacterial meningitis until CSF results are available, and start IV aciclovir if HSV meningitis or encephalitis cannot be excluded. IV aciclovir can be discontinued once HSV PCR is negative (provided there is no encephalitic component).

Supportive care: analgesia (paracetamol, codeine), antiemetics, IV fluids if dehydrated.
IV aciclovir 10 mg/kg Q8H if HSV meningitis suspected (continue until CSF HSV-2 PCR result known).
HSV-2 meningitis treatment (if confirmed): IV aciclovir 10 mg/kg Q8H for 7–10 days, or valaciclovir 1 g PO TDS for 7–10 days if mild and tolerating oral intake.
Recurrent HSV-2 meningitis (Mollaret): prophylactic valaciclovir 500 mg PO daily long-term.

Encephalitis & Autoimmune Encephalitis

Infectious Encephalitis

Encephalitis is defined as inflammation of the brain parenchyma, characterised by altered consciousness or personality change, seizures, or focal neurological signs, in combination with CSF, EEG, or neuroimaging evidence of inflammation. It is distinguished from meningitis by the presence of brain dysfunction (not just meningeal irritation).

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HSV encephalitis is a medical emergency. IV aciclovir must be started immediately on clinical suspicion — within 30 minutes if possible. Every hour of delay in aciclovir initiation increases mortality and morbidity. Mortality without treatment exceeds 70%; even with treatment, ~20% die and ~50% have significant neurological sequelae.

Common Causes of Encephalitis in Australia

Category	Organism / Cause	Key Features
Herpes viruses	HSV-1 (most common sporadic cause), HSV-2, VZV, HHV-6, CMV, EBV	HSV-1: temporal lobe involvement, olfactory hallucinations, personality change, aphasia. MRI: temporal lobe oedema/haemorrhage.
Arboviruses	Murray Valley encephalitis virus (MVEV), Kunjin virus, Japanese encephalitis virus (JEV), West Nile virus	JEV emerged in SE Australia in 2022; associated with pig farms and Culex mosquitoes. MVEV in northern WA and NT during wet season.
Enteroviruses	Enterovirus 71, EV-A71	Brainstem encephalitis in children, associated with hand-foot-and-mouth disease.
Measles, mumps	Measles morbillivirus, mumps virus	Rare in vaccinated populations. Measles SSPE is delayed (years).
Rabies / ABLV	Australian bat lyssavirus (ABLV)	Exposure to bat bites/scratches in Australia. Post-exposure prophylaxis essential. Extremely rare but nearly always fatal.
Bacterial	Mycoplasma pneumoniae, Rickettsia, Coxiella burnetii (Q fever)	May present with encephalitis as part of systemic infection.

Empirical Treatment for Suspected Encephalitis

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Aciclovir

Zovirax® · Antiviral (anti-herpes)

Adult dose 10 mg/kg IV Q8H (based on ideal body weight; use adjusted body weight if obese)

Paediatric dose 20 mg/kg IV Q8H (>3 months); 20 mg/kg IV Q12H (neonates)

Duration 14–21 days for HSV encephalitis; 7–10 days for other herpesvirus

Renal adjustment eGFR 25–50: 10 mg/kg Q12H; eGFR 10–25: 10 mg/kg Q24H; eGFR <10: 5 mg/kg Q24H

Key monitoring Ensure adequate IV hydration (≥1 L/1.73 m²/day); monitor serum creatinine Q48H; risk of crystalline nephropathy

PBS status ✔ PBS General Benefit

In addition to IV aciclovir, empirical treatment should include IV ceftriaxone + ampicillin (if Listeria risk) to cover bacterial meningitis until CSF results are available.

Autoimmune Encephalitis

Autoimmune encephalitis is an increasingly recognised cause of encephalitis that mimics infectious encephalitis but is mediated by auto-antibodies against neuronal surface or intracellular antigens. It is estimated to account for 10–20% of encephalitis cases previously labelled as "idiopathic" in Australian tertiary centres.

Key Autoimmune Encephalitis Syndromes

Antibody	Demographics	Clinical Features	Association
Anti-NMDA receptor	Young women (median 21 years); also children and older adults	Psychiatric symptoms (psychosis, agitation), seizures, orofacial dyskinesias, autonomic instability, decreased consciousness, hypoventilation	Ovarian teratoma (50–60% of adult women)
Anti-LGI1	Older adults (median 60 years), M>F	Faciobrachial dystonic seizures, rapidly progressive cognitive decline, hyponatraemia	Rare tumour association
Anti-CASPR2	Older adults, M>F	Neuromyotonia, neuropathic pain, Morvan syndrome, cognitive decline	Thymoma
Anti-AMPAR	Older adults	Limbic encephalitis, memory loss, psychiatric symptoms	SCLC, thymoma, breast cancer
Anti-GABA-B receptor	Older adults	Prominent seizures, limbic encephalitis	SCLC (50%)
Anti-GAD65	Young to middle-aged adults	Stiff-person spectrum, cerebellar ataxia, seizures	Type 1 diabetes, thymoma

When to Suspect Autoimmune Encephalitis

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Subacute onset (weeks to months) of working memory deficits, altered mental status, or psychiatric symptoms.
New-onset seizures (especially faciobrachial dystonic seizures), movement disorders (orofacial dyskinesias, chorea), or autonomic dysfunction.
CSF with lymphocytic pleocytosis (but can be normal in up to 50% of anti-LGI1/anti-NMDA receptor cases).
Infectious encephalitis workup is negative or partially negative.
Consider in any patient with new psychiatric symptoms + seizures or movement disorder, particularly in young women (anti-NMDA receptor) or older men with hyponatraemia (anti-LGI1).

Treatment of Autoimmune Encephalitis

First-Line Immunotherapy

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Methylprednisolone

Solu-Medrol® · Corticosteroid

Adult dose 1 g IV daily for 3–5 days, then oral prednisolone 1 mg/kg/day tapered over 6–8 weeks

PBS status ✔ PBS General Benefit

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Intravenous Immunoglobulin (IVIg)

Privigen®, Intragam P®

Adult dose 0.4 g/kg/day IV for 5 days (total 2 g/kg) — given concurrently with or sequentially after methylprednisolone

PBS status Authority Required

Second-line immunotherapy (for refractory cases or inadequate response to first-line at 2 weeks): Rituximab 375 mg/m² IV weekly for 4 weeks, and/or cyclophosphamide 750 mg/m² IV monthly for 6 months. Specialist rheumatology/immunology input is essential.

Tumour treatment: In anti-NMDA receptor encephalitis, ovarian teratoma removal is critical and should be pursued urgently with pelvic MRI and/or ultrasound in all women. In older adults, screen for underlying malignancy (CT chest/abdomen/pelvis, PET-CT if indicated).

Brain Abscess & Subdural Empyema

A brain abscess is a focal collection of pus within the brain parenchyma, surrounded by a vascularised capsule. A subdural empyema is a collection of pus between the dura mater and arachnoid mater. Both are neurosurgical emergencies that require a combined approach of antimicrobial therapy, neurosurgical drainage, and identification/treatment of the underlying source.

Aetiology & Predisposing Factors

Source / Route	Common Organisms	Proportion
Contiguous spread (sinusitis, otitis media, mastoiditis, dental infection)	Streptococci (viridans group, S. milleri group), Bacteroides, Fusobacterium, Prevotella	~40%
Haematogenous (endocarditis, pulmonary AV malformations, dental infection)	Streptococci, S. aureus, Gram-negatives	~25%
Post-traumatic / post-neurosurgical	S. aureus, coagulase-negative staphylococci, Gram-negatives	~15%
Cryptogenic (no identified source)	Mixed flora common	~20%
Immunocompromised (HIV, transplant)	Toxoplasma gondii, Nocardia, Aspergillus, Cryptococcus	Variable

Clinical Presentation

Headache — progressive, often severe and unremitting; the most common presenting symptom (70–90%).
Fever — may be absent in up to 50% of cases, especially in partially treated or immunocompromised patients.
Focal neurological deficit — depends on location (hemiparesis, dysphasia, cerebellar signs, cranial nerve palsies).
Seizures — focal or generalised, occur in 25–35% of cases.
Nausea and vomiting — raised intracranial pressure.
Papilloedema — if present, indicates significant raised ICP — contraindication to LP.
Subdural empyema — rapid clinical deterioration, high fever, focal deficits, signs of raised ICP; progresses faster than brain abscess and has higher mortality (15–30%).

Investigations

CT brain with IV contrast — ring-enhancing lesion(s). Sensitivity ~95% for abscesses >1 cm. Low sensitivity in early cerebritis phase.
MRI brain with gadolinium — superior sensitivity; DWI (diffusion-weighted imaging) distinguishes abscess (restricted diffusion) from tumour (facilitated diffusion). Preferred if available and patient is stable.
CT / MR venogram — if dural sinus thrombosis is suspected (especially with adjacent sinusitis).
Blood cultures — positive in 20–30% of cases.
Stereotactic aspiration / surgical drainage — essential for microbiological diagnosis (Gram stain, culture, acid-fast stain, fungal culture, PCR). Abscess fluid is superior to blood cultures for organism identification.
Immunocompromised patients — also test for Toxoplasma IgG, Nocardia culture, Aspergillus galactomannan/β-D-glucan, HIV test if not already known.

⚠️

Do NOT perform lumbar puncture in suspected brain abscess or subdural empyema. LP in the setting of a space-occupying lesion risks cerebral herniation and is of limited diagnostic value. Diagnosis is made by neuroimaging and aspiration.

Treatment

Empirical Antimicrobial Therapy (Community-Acquired, Immunocompetent)

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Ceftriaxone

Rocephin® · 3rd-generation cephalosporin

Adult dose 2 g IV Q12H

PBS status ✔ PBS General Benefit

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Metronidazole

Flagyl® · Nitroimidazole (anti-anaerobic)

Adult dose 500 mg IV Q8H (excellent CNS and abscess penetration)

Duration 4–8 weeks total (IV for 2–4 weeks, then switch to oral if clinical improvement)

Renal adjustment No adjustment required

PBS status ✔ PBS General Benefit

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Vancomycin

Various · Glycopeptide

Adult dose 25–30 mg/kg loading dose, then 15–20 mg/kg Q8–12H (trough 15–20 mg/L) — add if MRSA risk (post-neurosurgical, CA-MRSA in remote communities)

PBS status ✔ PBS General Benefit

Neurosurgical Management

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Surgical drainage is indicated for:

Abscess >2.5 cm in diameter.
Abscess in the posterior fossa (risk of brainstem compression).
Significant mass effect with midline shift.
Failure to improve on antibiotics after 1–2 weeks.
Multiloculated or gas-containing abscess.
Subdural empyema — always requires urgent surgical evacuation.

Stereoactic aspiration (CT-guided) is the preferred initial approach. Open craniotomy may be needed for multiloculated abscesses or empyemas. Serial aspirations may be required.

Adjunctive Measures

Corticosteroids: Dexamethasone is NOT routinely recommended for brain abscess. Consider only if significant mass effect and risk of herniation, and in consultation with neurosurgery. Dexamethasone may impair abscess capsule formation and reduce antibiotic penetration.
Antiepileptic drugs: Prophylactic levetiracetam 500–1000 mg PO/IV BD is commonly used for 3–6 months. Discontinue if no seizures occur and EEG is normal. (PBS: General Benefit)
DVT prophylaxis: Low-molecular-weight heparin (enoxaparin 40 mg SC daily) once post-operative haemorrhage risk is acceptable.
Treatment of source: Simultaneously manage the primary source (e.g., mastoidectomy for otogenic abscess, dental extraction, sinus surgery, treatment of endocarditis).

Monitoring and Follow-Up

Serial MRI or CT brain every 2–4 weeks to assess abscess resolution.
Duration of antibiotics: typically 4–8 weeks total (guided by clinical response, CRP/ESR trends, and imaging). Some guidelines recommend continuing antibiotics until the abscess cavity has reduced to <1 cm.
Monitor inflammatory markers (CRP, ESR) weekly.
Neuropsychological assessment for long-term cognitive follow-up.
Seizure recurrence risk — long-term AED may be needed if seizures occurred during acute illness.

Risk Stratification & Severity Scoring

Bacterial Meningitis — Glasgow Meningococcal Septicaemia Prognostic Score

While various prognostic scores exist, the following clinical features identify high-risk patients requiring intensive care admission:

Lower Risk

Community-Onset, Immunocompetent

GCS 15, no sepsis criteria, no petechial rash, no coagulopathy, no focal deficits. CSF with classic bacterial meningitis pattern but patient appears well.

Setting: Inpatient ward with close monitoring

Moderate Risk

Deteriorating or Comorbid

GCS 12–14, tachycardia, hypotension responding to fluids, petechiae without purpura, focal neurological signs. Age >60, immunocompromise, alcohol use disorder.

Setting: HDU / ICU with close neurological monitoring

High Risk

Meningococcal Septicaemia / Cerebral Oedema

GCS <12, septic shock, purpura fulminans, DIC, seizures, signs of raised ICP (papilloedema, Cushing response), impending herniation. Rapidly progressive deterioration.

Setting: ICU with intubation capability, neurosurgical consult

Encephalitis — Clinical Decision Points

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ICU admission criteria for encephalitis: GCS ≤12, seizures (especially status epilepticus), respiratory compromise, autonomic instability (anti-NMDA receptor encephalitis), raised ICP. Patients with suspected HSV encephalitis should be managed in a monitored environment for at least the first 48–72 hours of aciclovir therapy.

Investigations

Essential Lumbar puncture with CSF analysis Cell count and differential, glucose (paired serum glucose), protein, Gram stain, culture, bacterial antigen testing, multiplex PCR (bacterial/viral). Send 3–4 tubes. Opening pressure measurement is essential. Available at all Australian hospitals. MBS item 138 (LP) and MBS items for CSF analysis.

Essential CSF multiplex PCR panel Detects HSV-1, HSV-2, VZV, enterovirus, N. meningitidis, S. pneumoniae, Listeria, E. coli K1, Haemophilus, GB viruses. Turnaround 2–6 hours in most tertiary centres; 12–24 hours in regional labs. Sensitivity >95% for HSV encephalitis when collected >72 hours after onset.

Essential Blood cultures (2 sets) Before antibiotics if possible. Positive in 50–70% of N. meningitidis cases and 30–40% of pneumococcal meningitis. Available at all hospitals.

Essential CT brain (± IV contrast) Required BEFORE LP in patients with focal deficits, seizures, GCS <12, papilloedema, immunocompromise, age ≥65. With contrast: ring-enhancing lesion in brain abscess. Available at all Australian hospitals and most regional centres.

Available MRI brain with gadolinium Superior for HSV encephalitis (temporal lobe hyperintensity on DWI/FLAIR), brain abscess characterisation, and leptomeningeal enhancement. Typically available at metropolitan centres within 4–6 hours; regional transfer may be needed.

Available CSF autoimmune antibody panel Anti-NMDA receptor, anti-LGI1, anti-CASPR2, anti-AMPAR, anti-GABA-B, anti-GAD65 antibodies. CSF is preferred over serum. Sent to reference labs (e.g., Royal Melbourne Hospital Neuroimmunology Laboratory). Turnaround 5–14 days. Consider sending early even if infection suspected.

Available CT / MRI with venogram If dural sinus thrombosis suspected (adjacent sinusitis, mastoiditis). Available at metropolitan centres.

Specialist Stereotactic brain biopsy / aspiration For brain abscess >2.5 cm or failing medical therapy. Performed by neurosurgery. Essential for microbiological diagnosis of abscess contents. Available at tertiary neurosurgical centres (transferred from regional if needed).

Available EEG (electroencephalography) Supports diagnosis of encephalitis (temporal lobe periodic discharges in HSV, generalised slowing). Status epilepticus detection. Available at most tertiary and some regional centres with neurology support.

Available Serum cryptococcal antigen (CrAg), HIV serology CrAg lateral flow assay is rapid (15 minutes), highly sensitive/specific. HIV testing should be offered to all patients with unexplained encephalitis or cryptococcal meningitis. Available at all Australian pathology services.

When CT is Required Before Lumbar Puncture

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Perform CT brain before LP if ANY of the following are present:

Immunocompromised state
History of CNS disease (mass lesion, stroke, focal infection)
New-onset seizures (within 1 week)
Papilloedema
GCS <12 or fluctuating consciousness
Focal neurological deficit (excluding cranial nerve palsy)
Age ≥65 years

Do not delay antibiotics while waiting for CT — administer IV ceftriaxone, dexamethasone (± ampicillin ± aciclovir) immediately.

Special Populations

🤰 Pregnancy

Increased Listeria risk: Pregnancy is an independent indication for adding ampicillin to empirical meningitis therapy.

Aciclovir: Safe in pregnancy (Category B3). Treat HSV encephalitis aggressively — maternal mortality is high without treatment.

Dexamethasone: Generally recommended in bacterial meningitis in pregnancy (benefit outweighs risk). Short courses are not associated with teratogenicity.

Valproate: Avoid for seizure prophylaxis (teratogenic). Use levetiracetam instead.

Metronidazole: Avoid in first trimester if possible; acceptable in second/third trimester for serious infections.

LP in pregnancy: Safe at all gestations. May need lateral decubitus position in third trimester. Monitor for post-dural puncture headache.

👶 Paediatrics

Neonatal meningitis (<1 month): Empirical therapy: ampicillin + cefotaxime (or gentamicin). Ceftriaxone is avoided in neonates due to biliary sludging and bilirubin displacement. Duration: 21 days for GBS, ≥21 days for Gram-negative bacilli.

Infants 1–3 months: Ampicillin + ceftriaxone (covers Listeria, GBS, Gram-negatives, meningococcus, pneumococcus).

Children >3 months: Ceftriaxone 100 mg/kg/day (max 4 g) ± dexamethasone (0.15 mg/kg Q6H for 4 days; most beneficial in H. influenzae meningitis).

HSV encephalitis in neonates: Aciclovir 20 mg/kg IV Q8H for 21 days (longer course than adults due to higher relapse risk).

Anti-NMDA receptor encephalitis: Important differential in children presenting with new-onset psychiatric symptoms, seizures, and movement disorders. Paediatric ovarian teratoma is rare but must be excluded in girls.

Enteroviral meningitis: Common and usually benign in children. Supportive care only. Ensure CSF enterovirus PCR is sent to avoid unnecessary prolonged antibiotic courses.

👴 Elderly (≥65 years)

Higher Listeria risk: Always add ampicillin to empirical regimen in patients >50 years.

Gram-negative bacilli: More common causative organisms in the elderly, including E. coli, Klebsiella spp.

Atypical presentation: Meningism may be absent. Confusion and delirium may be the only presenting feature.

Higher mortality: Case fatality rates for bacterial meningitis are 30–40% in the elderly, compared to 10–15% in younger adults.

Renal dose adjustment: Renal impairment is common — adjust aciclovir, gentamicin, vancomycin dosing. Use estimated GFR for calculations.

Dexamethasone: Benefit in pneumococcal meningitis persists in the elderly — continue unless contraindicated.

🫘 Renal Impairment

Aciclovir: Significant nephrotoxicity risk. Reduce dose: eGFR 25–50 → 10 mg/kg Q12H; eGFR 10–25 → 10 mg/kg Q24H; eGFR <10 → 5 mg/kg Q24H. Ensure aggressive IV hydration. Haemodialysis removes aciclovir — supplemental dose post-dialysis.

Vancomycin: Dose adjust per AUC-guided dosing (target AUC/MIC 400–600). Therapeutic drug monitoring essential.

Gentamicin: Use extended-interval dosing with therapeutic drug monitoring. Avoid if possible in severe CKD.

Ceftriaxone: No adjustment required (biliary elimination).

Penicillins (ampicillin, penicillin G): Reduce dose and/or extend interval if eGFR <30 mL/min.

IVIg (autoimmune encephalitis): Use with caution — risk of acute kidney injury, especially with sucrose-containing formulations. Prefer sucrose-free products (e.g., Privigen®).

🫁 Hepatic Impairment

Valproate: Contraindicated in significant hepatic impairment (encephalitis seizure prophylaxis). Use levetiracetam or phenytoin instead.

Metronidazole: Use with caution; risk of hepatotoxicity. Monitor LFTs.

Ceftriaxone: Avoid in neonates with hyperbilirubinaemia. In adults with severe liver disease, biliary elimination may be impaired — monitor closely (though dose adjustment not usually required).

Chronic liver disease increases Listeria susceptibility — always add ampicillin in this population.

🛡️ Immunocompromised

Broader empirical coverage required: Add ampicillin (Listeria), consider vancomycin, and add antifungals if clinical suspicion (fluconazole for Cryptococcus, voriconazole for Aspergillus). Consider Toxoplasma coverage in HIV with CD4 <100 (sulfadiazine + pyrimethamine).

Cryptococcal meningitis: Suspect in HIV with CD4 <100, presenting with subacute headache, raised ICP. CSF CrAg is diagnostic. Treatment: amphotericin B (liposomal) + flucytosine for 2 weeks, then fluconazole 400 mg daily for 8 weeks, then 200 mg daily maintenance.

CMV encephalitis: Consider in transplant recipients and advanced HIV. Ganciclovir 5 mg/kg IV Q12H + foscarnet 90 mg/kg IV Q12H.

Brain abscess in immunocompromised: Consider Nocardia, Toxoplasma, Aspergillus. Brain biopsy is often required. Empirical treatment should include trimethoprim-sulfamethoxazole (Nocardia, Toxoplasma) and/or voriconazole (Aspergillus).

IRIS (immune reconstitution inflammatory syndrome): In HIV patients starting ART, paradoxical worsening of CNS infection may occur. Manage with corticosteroids and continue ART.

Aboriginal and Torres Strait Islander Health

Aboriginal and Torres Strait Islander Australians experience a disproportionately high burden of CNS infections compared with non-Indigenous Australians. This disparity is driven by a combination of higher rates of bacterial colonisation, lower vaccination coverage, higher prevalence of comorbidities (chronic kidney disease, rheumatic heart disease, diabetes), remote geography limiting access to timely care, and systemic barriers to healthcare access.

Invasive pneumococcal disease

Aboriginal and Torres Strait Islander Australians have 5–8 times higher incidence of invasive pneumococcal disease compared with non-Indigenous Australians, with higher rates of serotypes not covered by the 13-valent conjugate vaccine. The 23-valent polysaccharide vaccine (Pneumovax 23®) is recommended for all Indigenous adults ≥50 years and ≥15 years with risk factors (NHMRC Australian Immunisation Handbook).

Invasive meningococcal disease

Rates are approximately 3–4 times higher in Indigenous Australians, particularly serogroup W in the Northern Territory. MenB vaccine (Bexsero®) and MenACWY vaccine (Nimenrix®) are funded on the NIP for Aboriginal and Torres Strait Islander children in specific jurisdictions — check state/territory schedules.

Remote and rural access

Many Aboriginal and Torres Strait Islander communities are in remote or very remote areas with limited access to CT/MRI, lumbar puncture capability, neurosurgical services, and ICU. Evacuation for suspected CNS infection may involve delays of several hours. Primary care clinicians in remote clinics must be empowered to initiate empirical antibiotics and dexamethasone immediately on clinical suspicion and arrange urgent retrieval.

CA-MRSA in remote communities

Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA), particularly the Panton-Valentine leucocidin (PVL)-positive clone, has high prevalence in remote Northern Territory and Western Australian communities. Consider vancomycin in empirical brain abscess regimens in these populations.

Delayed presentation

Aboriginal and Torres Strait Islander patients with CNS infections are more likely to present at a later stage of disease with worse clinical outcomes. Delays are related to geographical distance, cultural factors, previous negative healthcare experiences, and limited availability of culturally safe services. Primary care providers in Indigenous health should maintain a low threshold for empirical treatment.

Cultural safety in acute care

Patients from remote communities may require family support and cultural liaison services when evacuated for treatment. Avoidance behaviours are common — ensure culturally safe communication, use of interpreters where English is not the first language (many Indigenous Australians speak a first language other than English), and involve Aboriginal and Torres Strait Islander health workers in the care team. Respect Sorry Business and kinship obligations.

⚠️

Practical recommendation for remote primary care: In any Aboriginal or Torres Strait Islander patient presenting with fever, headache, neck stiffness, altered consciousness, or new seizures in a remote clinic, administer IV/IM ceftriaxone 2 g (adults) or 50 mg/kg (children), IV dexamethasone 0.15 mg/kg, and IV aciclovir 10 mg/kg (if encephalitis suspected) immediately. Do not delay treatment to arrange transfer. Document and contact retrieval services simultaneously.

📚 References

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6. Brouwer MC, Tunkel AR, van de Beek D. Brain abscess. N Engl J Med. 2024;390(12):1085-1095. doi:10.1056/NEJMra2307415
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8. Australian Government Department of Health and Aged Care. The Australian Immunisation Handbook. 12th ed. Canberra: Australian Government Department of Health and Aged Care; 2024. Available at: https://immunisationhandbook.health.gov.au
9. Australian Institute of Health and Welfare (AIHW). Aboriginal and Torres Strait Islander Health Performance Framework. Canberra: AIHW; 2023. Available at: https://www.aihw.gov.au/reports-data/population-groups/aboriginal-torres-strait-islander-people
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13. Communicable Diseases Network Australia (CDNA). Guidelines for the Early Clinical and Public Health Management of Meningococcal Disease in Australia. Canberra: Australian Government Department of Health; 2017.
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15. NT Government Department of Health. Central Australian Rural Practitioners Association (CARPA) Standard Treatment Manual. 8th ed. Alice Springs: CARPA; 2022. [Reference for remote primary care management of CNS infections in Indigenous communities]