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New C. difficile testing protocol at Salem Health

17 Feb 2019

By: Jasmin Chaudhary M.D.

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Beginning Feb. 18, 2019, Salem Health lab will introduce a new C. diff testing protocol. Our current testing protocol uses a stand-alone PCR-NAAT test (Polymerase chain reaction-nucleic amplification assay test), which detects the gene for C. diff toxin A and B. Unfortunately, this test cannot tell us if the gene is producing active toxin or not. It has a high sensitivity for detecting the gene in general, but poor positive predictive value for detecting active toxin production which would be clinically significant. This often leads to overdiagnosis, increased hospital stays, and may lead to unnecessary treatment. In light of this, we have elected to adopt a multi-analyte approach to testing based on IDSA (Infectious Disease Society of America) and ESCMID (European Society of Clinical Microbiology and Infectious Disease) guidelines.

Salem Health lab will now reflex all positive PCR-NAAT results to a rapid diagnostic toxin A/B test that has been brought on-site. There is no need to order any additional tests. Negative PCR tests will not reflex. Based on studies, this approach increases the positive predictive value for true C. diff cases. Patients who are positive by PCR and positive for toxin are deemed to have true C. diff disease. Patients with positive PCR, but negative toxin, may be carriers and may have alternate causes for diarrhea. Clinical correlation is recommended. Based on NHSN (CDC’s National Healthcare Safety Network) reporting criteria, patients with a negative toxin test will be deemed “carriers” and will not be classified as true C. diff infection.

Patients awaiting C diff test results, and all those with a positive PCR should be placed in contact plus precautions to prevent transmission.  Contact plus precautions can be removed if PCR results are negative.  Patients with positive PCR results, regardless of toxin A/B results should remain in contact plus precautions until they are diarrhea-free for 72 hours because colonized patients or “carriers” still contribute to transmission.  At that time, we are advising a terminal clean of the room prior to removal of isolation, and we currently UV light these rooms post-terminal clean. Patients will likely require moving to another room during the terminal clean. 

Thank you for your cooperation. The most important thing we can do is to send off the test for C. diff when it is clinically appropriate. In addition, we hope that by switching to a multi-analyte approach, we will better able to identify true cases of C. diff infection.

LAB7105 C.DIFFICIILE BY PCR WITH REFLEX TOXIN ASSAY. Positive pcr results will continue to be called.

Toxin confirmation is done before 9 a.m. Positives are not called.

For more information please feel free to contact Julie Koch, Infection Prevention Manager and Jasmin Chaudhary, Infection Prevention Medical Director.