CSF shunt infections and their microbiological diagnosis Dr Roger Bayston MMedSci FRCPath University Hospital, Nottingham.

CSF shunt infections and their microbiological diagnosis

Dr Roger BaystonMMedSci FRCPath

University Hospital, Nottingham

Hydrocephalus

• Caused by obstruction of CSF pathways • Can occur at any age• Can follow meningitis (Incl TBM)

haemorrhage (SAH, PVH etc)

trauma

tumours

congenital malformations

intrauterine infections

Examples

• Congenital hydrocephalus

Diagnosis:

Hydrocephalus due to toxoplasmosis in utero

Hydrocephalus shunts

Direction of flow

Routes of shunting

Ventriculoperitoneal Ventriculoatrial

Definition of shunt infection

• External: infection around the outside of the shunt. Failure to heal, or post-operative wound breakdown. Not a true shunt infection but a surgical wound infection.

• Internal: colonisation of the inner surfaces of the shunt tubing with or without involvement of the cerebral ventricles.

External “shunt infection”

Internal (true) shunt infection

Post -op erythema, swelling

Bacteria growing on inside of shunt catheter

About 5% of infections

About 95% of infections

Incidence of shunt infection• Cited as “10% of operations”

• But: children and adults: 3-6%

Infants ≤ 6mo old, 10 - 25%

Medical consequences• Ventriculitis• Secondary infection from EVD• Frequent relapse and need for re-operation• Loculated ventricles

Often presents as distal obstruction

•Peritonitis•Peritoneal cysts, abscesses •Loss of absorptive capacity

Causative organisms

• Staphylococcus epidermidis (and other CoNS)• S aureus (some MRSA)• Propionibacterium acnes• Coryneforms• Other gram positives• Gram negatives• Candida

Pathogenesis of shunt infections

• Adherence of bacteria to inner surface of shunt

• Bacterial proliferation (slow!)

• Biofilm development

Pathogenesis of shunt infection

Time

shunt surface

Conditioning film

Biofilm

Exopolymer “slime” or PIA

mic 1mg/L

mic >500mg/Lmic >50mg/L

Biofilm formation in shunts

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Staphylococci, SEM X 16300

Staphylococci, SEM X 5400

Why are biofilm phenotypes less susceptible to antibiotics?• Nutrient depletion leads to problems with

energy generation and transport• This causes phenotype change to conserve

energy• All non - essential functions are down -

regulated• These include cell wall synthesis, protein

synthesis and DNA replication

• This state is “dormant” or “SCV”

SCVs (Dormant biofilm phenotypes)

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SCVs usually revert to

“textbook” appearance after a

few subcultures

They are identical on APIStaph and

PFGE

SCVs from a recent VA case

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Blood culture

Sub BA 48hr

CSF broth subculture

BA O/N

Gram film from fluid in removed shunt

Longstanding shunt infections can give direct gram films showing pleomorphism and uneven staining

Diagnosis of VP shunt infection

• ≤ 6mo since operation• Positive CRP• Return of hydrocephalus (distal obstruction)• Erythema over catheter track• Positive shunt tap (Gram stain! and culture)• Pyrexia

Laboratory diagnosis

• Blood culture - but rarely positive in VP

In VA, usually positive in early stages but often negative in late - presenting infections.

Problems with contaminants• Serology: ASET for VA infections, not VP

CRP for VP infections• Shunt tap: can give normal CSF

CRP in VP shunt infection

Operation 5 days 10 days 15 days +

10mg/L

Examination of removed shunts

Method A• Shunt examined carefully• Any pus or tissue on outside sampled• Outside surface cleaned with a steret• Fluid from inside of each component aspirated• Gram film, aerobic + anaerobic culture, up to 7 days (more if bacteria

seen)

Method B

• Place removed shunt catheters into TSB, shake and incubate O/N then subculture onto BA

Examination of removed shunts: does the method make a difference?

Organisms Method A Method BCoNS 4 22S aureus 1 3Coryneform 0 1Mixed 1 7Gram film only +ve 2Negative 25 1

Total 34 34

Clinically infected shunt 8 8

Examination of removed shunts: does the method make a difference?

Organisms Method A Method BCoNS 4 22S aureus 1 3Coryneform 0 1Mixed 1 7Gram film only +ve 2Negative 25 1

Total 34 34

Clinically infected shunt 8 8

Prevention: Prophylactic antibiotics?• Commonly used (85% of UK surgeons)

• Usually iv cephalosporin or gentamicin

• Neither reaches CSF !

• Most staphylococci resistant !

• No statistically valid trials!

No evidence of efficacy

(BSAC Working Party on Neurosurgical Infection)

Possible use of antimicrobial biomaterial

Antimicrobial shunts

Bacteria adhere to the shunt, then die

Early clinical experience with antibacterial shunts

• Approx 30,000 used worldwide• Expected infections: approx 3000• Reported so far (4.5yrs): 46

Three clinical trials reported so far:

•Govender et al 2003: J Neurosurg 99:831-839:Gram positive infection rate reduced from 16.7% to zero

•Aryan et al 2005: Child’s Nerv Syst 21: 56-61:Infection rate reduced from 15.2% to 3.1% (1 case)

•Scubbe et al 2005 (conference report):Infection rate reduced from 9% to 2% (291 cases, p=0.025)

The End