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CPE Screening
We are grateful to Dr Andrew Dodgson, Consultant Microbiologist, Public Health
England and Central Manchester Hospitals NHS Foundation Trust
Educational Workshops 2016
Keynote
Terminology
• CPECarbapenemase Producing Enterobacteriaceae
• CRE Carbapenem Resistant Enterobacteriaceae
• CPOCarbapenemase Producing Organism
• CRO Carbapenem Resistant Organism
Classification of carbapenemases
• Class A (serine based)• KPC, GES, SME, NMC, IMI
• Class B (metallo‐enzymes)• NDM, IMP, VIM, GIM, SIM, SMP, L1, BCII, Ccra
• Class D (serine)• OXA
Queenan and Bush, CMR 2007
Classification
• Chromosomal– Class A
• SME, NMC, IMI
– Class B• BCII, L1, Ccra
• Plasmid– Class A
• KPC, GES
– Class B• NDM, IMP
– Class D• OXA
Queenan and Bush, CMR 2007
What’s worth worrying about?
• All of them?• The “Big 5”
– KPC– VIM– NDM– IMP– OXA‐48 like
Diversity
• Molecular characteristics
• Substrate profile• Activity against carbapenems
• Host species…….
• Compare with MRSA
Implications for:• Detection• Therapy• Control?
Global Distribution‐KPC
From: Lee et al., Front Microbiol. 2016 Jun 13;7:895
Global Distribution‐NDM
From: Lee et al., Front Microbiol. 2016 Jun 13;7:895
Global Distribution‐OXA‐48
From: Lee et al., Front Microbiol. 2016 Jun 13;7:895
http://www.ecdc.europa.eu/en/healthtopics/antimicrobial_resistance/database/Pages/map_reports.aspx
A UK Perspective
Number of isolates referred from UK hospital microbiology laboratories confirmed as carbapenemase‐producing Enterobacteriaceae by AMRHAI, 2003−2014.
Klebsiella pneumoniae Carbapenemase (KPC)
• 1st described from an isolate in a surveillance project from 19961
• Plasmid mediated• Disseminated throughout eastern seaboard during early 2000’s
• Rate of carbapenem resistance in K. pneumoniae from NY went from 0.1% to 22% between 1999‐20062
1Yigit et al. Antimicrob Agents Chemother. 2001 Apr;45(4):1151-61. 2Landman et al. J Antimicrob Chemother. 2007 Jul;60(1):78-82.
Control‐What can we do?
• Find carriers• Screening
• Isolate carriers• Eliminate vectors
• Hand hygiene• Clean equipment
• Clean environment • Change host environment
• Antibiotic policy
Control
Screening
• Who, when & how often?– On Admission– Any patient who in the last 12 months has:
• Been an inpatient in a hospital abroad OR • Been an inpatient in a UK hospital known to have had problems with spread of carbapenemase‐producing Enterobacteriaceae
OR • Previously been colonised or had an infection with carbapenemase‐producing Enterobacteriaceae or close contact with a person who has, if known
– 3 screens 48hrs apart
MIC’s of Carbapenemase producers
ECOFF S I RErta >0.125 ≤0.5 1 >1
0.5->64Imi >1 ≤2 4-8 >8
0.5->64Mero >0.125 ≤2 4-8 >8
0.25-64
Miriagou et al. Clin Microbiol Infect. 2010 Feb;16(2):112‐22.
Detection‐problems
MIC Determined by:• Presence, amount & type of carbapenemase• Porin loss• Presence & amount of other β‐lactamases (ESBL & AmpC)
Detection‐problems
Carbapenem resistance ≠ Carbapememase
ANDCarbapenemase ≠ Carbapenem
resistance
Detection Methodologies
Considerations:• Clinical sample vs. Screening samples• Prevalence
– Sporadic– Outbreak– Endemic
An approach to clinical samples
• Test ALL significant Enterobacteriaceae against a carbapenem
• Ertapenem most sensitive (least specific)– Problems with Enterobacter
• Speciate• Work up all showing non‐susceptibility• Don’t rely on expert rules of automated systems to identify potential CPE
Screening Methods
• Faecal sample or rectal swab– Need adequate sample if rectal swab* (~50% increased positivity rate,
for swabs with visibly faecal material, vs without)
• Enrichment vs. direct• Medium?
– Abx supplemented Mac or CLED– Mac or CLED with Carb disc– Commercial chromogenic
• Molecular
*Shorten, et al. JHI, 2016.
Screening Methods
• CDC method• 10ug Imi disc dropped in to 5ml TSB• Overnight incubation• Plated on to Mac
• Comparison of CDC and direct plating on Mac with 10ug Erta disk (≤27mm zone) *
– CDC, sens 65.6%, spec 49.6%– Direct, sens 97.0%, spec 90.5%
*Lolans et al, JCM 2010
CLED + Erta
ESBL Chromogenic + Erta
Negative Positive
Chromogenic media
• A number of formulations available• Difficult to critically assess performance• Likely to be optimised for KPC in particular• For example: 302 Turkish Pt’s screened (all who were +ve had OXA‐48)– CDC Method 58% sens, 95% spec– chromID Carba 58% sens, 99% spec– chromID OXA‐48 76% sens, 99% spec.
Zarakolu et al., ECCMID 2014
Molecular screening methods
• In‐House PCR• Commercial PCR
– A number available (Check‐Direct, EasyPlex, Cepheid)
– Variations in platform, cost, genes detected.– Direct comparisons not available
Molecular screening methods
• Potential advantages– Sensitivity– Turn around time– Genotype known immediately
• Disadvantages– COST– Lack of isolate for sensitivity/typing– Won’t detect novel/unusual mechanisms– Equipment/training
Molecular screening methods
Comparison of commercial PCR vs culture1:• Sens 96.6%, Spec 98.6%, PPV 95.3%, NPV 99%.• Results available in 32‐48 mins.UK experience2:• 67,801 samples tested by in‐house or commercial PCR, PCR +ves then cultured
• Only 81.7% of PCR +ve found to be culture +ve
1Tato, et al. JCM, 2016, 54(7):1814‐9. 2Shorten, et al. JHI, 2016.
Laboratory Methods
• Disc susceptibility– Interpretation, inoculum.
• E‐test– Microcolonies, interpretation
Detection Methods
• BSAC– Interpretation, inoculum.
• E‐test– Microcolonies, interpretation
• Automated systems (e.g. VITEK)– Variable performance, “expert” rule base may miss some
– e.g. may not call a carbapenemase unless all ceph’s resistant also
Confirmatory testing
Locally:• Is it needed?• Is it reliable?• Does it make a difference?
– Clinically?– Infection Control?
Confirmatory tests
• Modified Hodge Test• Phenotypic• Not specific to one enzyme• Within the capabilities of most labs• Subjective (to a degree)
“Cloverleaf test”
Negative MHT
Positive MHT
Synergy testing
Mechanism Carb + clav Carb + boronic acid
Carb + EDTA R to temocillin
MBL ‐ ‐ +++ +/‐
KPC +/‐ +++ ‐ +/‐
OXA‐48 ‐ ‐ ‐ +++
Confirmatory testing
PCR• Gold standard• Reference test• Commercial systems available• Recently published comparison
– no difference in performance between 3 commercial assays
Findlay et al., JAC, 2015; 70(5):1338‐42.
An unanswered question
Can we robustly determine loss of carriage?Do we rescreen patients known to be previously positive when readmitted?
– What does a negative mean?– Genuine or below limit of detection?– PCR more believable than culture?
Summary
• CPE represent a heterogenous group of species and mechanisms
• Laboratory detection from clinical specimens may require a high index of suspicion
• No one screening method will tick ALL the boxes