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Download New national guidelines for laboratory diagnosis of C.difficile infection
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New national guidelines for laboratory diagnosis of C.difficile infection • Enzyme immunoassays (EIAs) are not suitable as standalone tests • 2 step testing now required – Step 1. Screen using GDH (detects all C.difficile strains including non-toxigenic/non-pathogenic strains) – Step 2. Perform an EIA for toxin – Optional 3rd step. Perform PCR to further characterise GDH +ve, toxin –ve results i.e to determine whether patient is carrying potentially toxin producing C.difficile – Optional step 3 is included in the new NUH algorithm Next Interpreting toxin and PCR results • Positive toxin results – Patient’s diarrhoea may be due to infection with C.difficile – refer to C.difficile treatment guidelines – Patient is a cross-infection risk (if diarrhoea on-going) • Positive PCR results – PCR will only be done on toxin assay –ve samples – Patient’s diarrhoea is not likely to be due to C.difficile infection BUT patient is carrying C.difficile with the potential capability of making toxin – Patient is a cross-infection risk (if diarrhoea on-going) Next New diagnostic algorithm for C.difficile infection - NUH April 2012 Step 1. Screen liquid stool sample using GDH Test Positive Negative = C.difficile toxin Negative Step 2. Perform assay for C.difficile toxin Negative = C.difficile toxin Negative Positive = C.difficile toxin Positive Step 3. Perform PCR assay for C.difficile toxin genes on GDH +ve toxin assay –ve samples PCR Negative PCR Positive Patient is not a cross-infection risk Unlikely that C.difficile infection is cause of diarrhoea BUT patient is a cross-infection risk to others Next Results GDH screen negative C.difficile toxin assay not required PCR for toxin genes not required Example 1 NOTIS Report Next Results GDH screen positive C.difficile toxin assay negative PCR for toxin genes negative Example 2 NOTIS Report Next Results GDH screen positive C.difficile toxin assay negative PCR for toxin genes positive Example 3 NOTIS Report Next Results GDH screen positive C.difficile toxin assay positive (PCR for toxin genes not required) Example 4 NOTIS Report Next Results GDH screen positive C.difficile toxin assay negative PCR result awaited NOTIS Report (Interim) Example 5
