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CSF shunt infections and their microbiological diagnosis

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Title: CSF shunt infections and their microbiological diagnosis


1
CSF shunt infections and their microbiological
diagnosis
  • Dr Roger Bayston
  • MMedSci FRCPath
  • University Hospital, Nottingham

2
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

3
Examples
  • Congenital hydrocephalus

Diagnosis
Hydrocephalus due to toxoplasmosis in utero
4
Hydrocephalus shunts
Direction of flow
5
Routes of shunting
Ventriculoperitoneal
Ventriculoatrial
6
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.

7
External shunt infection
Post -op erythema, swelling
About 5 of infections
Internal (true) shunt infection
Bacteria growing on inside of shunt catheter
About 95 of infections
8
Incidence of shunt infection
  • Cited as 10 of operations
  • But children and adults 3-6
  • Infants 6mo old, 10 - 25

9
Medical consequences
  • Ventriculitis
  • Secondary infection from EVD
  • Frequent relapse and need for re-operation
  • Loculated ventricles
  • Peritonitis
  • Peritoneal cysts, abscesses
  • Loss of absorptive capacity

Often presents as distal obstruction
10
Causative organisms
  • Staphylococcus epidermidis (and other CoNS)
  • S aureus (some MRSA)
  • Propionibacterium acnes
  • Coryneforms
  • Other gram positives
  • Gram negatives
  • Candida

11
Pathogenesis of shunt infections
  • Adherence of bacteria to inner surface of shunt
  • Bacterial proliferation (slow!)
  • Biofilm development

12
Pathogenesis of shunt infection
Exopolymer slime or PIA
mic 1mg/L
Biofilm
mic gt50mg/L
mic gt500mg/L
Conditioning film
shunt surface
Time
13
Biofilm formation in shunts
Staphylococci, SEM X 5400
Staphylococci, SEM X 16300
14
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

15
SCVs (Dormant biofilm phenotypes)
SCVs usually revert to textbook appearance
after a few subcultures They are identical on
APIStaph and PFGE
16
SCVs from a recent VA case
Blood culture Sub BA 48hr
CSF broth subculture BA O/N
17
Gram film from fluid in removed shunt
Longstanding shunt infections can give direct
gram films showing pleomorphism and uneven
staining
18
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

19
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

20
CRP in VP shunt infection
10mg/L
Operation 5 days 10 days 15 days
21
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

22
Examination of removed shunts does the method
make a difference?
  • Organisms Method A Method B
  • CoNS 4 22
  • S aureus 1 3
  • Coryneform 0 1
  • Mixed 1 7
  • Gram film only ve 2
  • Negative 25 1
  • Total 34 34

Clinically infected shunt 8 8
23
Examination of removed shunts does the method
make a difference?
  • Organisms Method A Method B
  • CoNS 4 22
  • S aureus 1 3
  • Coryneform 0 1
  • Mixed 1 7
  • Gram film only ve 2
  • Negative 25 1
  • Total 34 34

Clinically infected shunt 8 8
24
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)

25
Possible use of antimicrobial biomaterial
26
Antimicrobial shunts
Bacteria adhere to the shunt, then die
27
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 99831-839
  • Gram positive infection rate reduced from 16.7
    to zero
  • Aryan et al 2005 Childs 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,
    p0.025)

28
The End
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