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Screening for Resistant
Organisms
Dr Koh Tse Hsien
Singapore General Hospital
How do you detect resistant
organisms?
Passive surveillance
Normal lab resultsNo extra work or costMay only pick up tip of the iceberg (20%)
Active surveillanceScreeningPicks up colonizationExtra work and cost
Why screen?
There is a problem
resistant bacteria affects patient morbidity and
mortality
infections with resistant bacteria increase costs
There is an intervention
isolation of patient
clearance of carriage
empirical treatment
What to screen
Vancomycin-resistant Enterococcus (VRE)
Methicillin-resistant Staphylococcus aureus(MRSA)
Extended-spectrum cephalosporin resistantEnterobacteriaceae
Carbapenemase-producingEnterobacteriaceae (CPE)
etc..
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How to screen
Culture
Selective agar
Non-culture
PCR
Selective agars
Antibiotic content allows selection of
resistance phenotype
Chromogenic indicator may allow presumptiveidentification
Takes at least 24 hours
Enrichment broth step?
Labor intensive
Allows isolation of strain for typing studies
PCR
May be more sensitive
Faster time to result
May be technically complex
Expensive
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MRSA Pooled nose, axilla, (throat), and perineal
swab
http://www.bd.com/ds/productCenter/215084.asp
http://www.bio-rad.com/
Enrichment or no enrichment?
Adding MRSA broth (ThermoScientific)
increased detection by 50% in SGH samples
But adds one extra days incubation to confirmpositive
http://www.rapidmicrobiology.com/news/603h120p.JPG
PCR
http://www.bd.com/geneohm/english/products/max/instrument/
http://www.cepheid.com/tests-and-reagents/clinical-ivd-test/xpert-mrsa
http://www.roche.com/products/product-details.htm?type=product&id=109
http://www.cepheidondemand.com/Summer-2011/cover-story.php
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David, M. Z. et al. 2010. Clin. Microbiol. Rev. 23(3):616-687
FIG. 2. Hypothetical virulence factors in USA300 and other CA-MRSA strains
VRE
Stool or rectal swab
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Vitek II
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Magnapure
Qiagen DNA minikit
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CPE
Stool or rectal swab
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5ml TSB+Meropenem disk
Meropenem 10 gdisk
MacConkey Agar with Imipenem DiskImipenem
Chromagar KPC
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ChromID ESBL
Cefpodoxime
MAST Adatabs
MacConkey +Meropenem 1 mg/L ChromID CARBA
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Direct from stool
Questions to ask yourself beforestarting surveillance
What is the target population?
Which resistant organisms do you want to
identify?
Which method?
What body sites to sample?
How long are you going to survey?
Admission surveillance or periodic surveillance?
Who pays? Is there will and money to intervene?
Modified from Best Practices in MDRO Screening and Control by Richard A van Enck