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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