csf shunt infections and their microbiological diagnosis dr roger bayston mmedsci frcpath university...
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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