Paul E. Sax, MD is the Editor-in-Chief, Journal Watch HIV/AIDS Clinical Care, Clinical Director of the Division of Infectious Diseases at Brigham and Women's Hospital, and Professor of Medicine at Harvard Medical School.
If you’re confused about the best way to diagnose C diff these days, welcome to the club. There are all kinds of tests out there, and no uniform approach between labs. Our lab actually does three tests — and will do a fourth (the classic cytotoxicity assay) if you request it.
The result? Chaos, confusion, and lots of queries.
For an example, here’s an email from a colleague:
Hey Paul — my patient had diarrhea after antibiotics, so I sent a C diff. Not sure what to tell her about the result, which I’ve pasted below. (She’s better now by the way with no treatment.)
Specimen Type: STOOL
C. DIFFICILE ANTIGEN/TOXIN ASSAY – Final
RESULTS PENDING PCR ANALYSIS.
TOXIGENIC CLOSTRIDIUM DIFFICILE QUALITATIVE BY PCR – NEGATIVE
Audrey — the lab does two rapid tests initially — antigen and toxin assay. She had a positive antigen (indicating the presence of the organism) but a negative toxin (not all C diff produces toxin). So the PCR was done as a more sensitive and specific test for toxin, and this was negative. Strongly suggests she does not have active C diff. No treatment required. Paul
Yes, this is tricky. Some labs go right to PCR as the first step, but this is more expensive — but it sure would eliminate the confusion.
Or we could just start using dogs. As demonstrated in this paper, and summarized in Journal Watch ID by Stephen Baum, a trained dog does a terrific job of diagnosing people with C diff, even without a specimen:
A 2-year-old male beagle was trained to identify the odor of toxin-producing C. diff and to sit or lie down on detection of this scent. In preliminary testing involving 50 positive and 50 negative stools, the dog’s sensitivity and specificity were 100% …[In further testing done in the hospital], the dog correctly identified 25 of the 30 case-patients (sensitivity, 83%) and 265 of the 270 controls (specificity 98%).
The most amazing thing about this study is not only the performance of the poop-sniffing dog, but the fact that he most likely enjoyed doing it. He’s a dog, after all.
Don’t believe me? Just Watch these two video clips. First, one from the BMJ paper (let’s hope that the beagle took his HIPAA training class seriously):
And second, this Cat vs. Dog short, which clearly demonstrates (around 1 minute in) why a dog is eager to help us diagnose C diff: