A 69-year-old man is discharged home from the hospital after a 10 day admission during which he underwent surgery for a benign tumor and received prophylactic antibiotics. Approximately 24 hours after discharge from the hospital, he experiences one day of diffuse watery diarrhea. Here are some gross and microscopic pictures of his colonic mucosa:

Which of the following organisms most likely caused these findings?

A. Shigella
B. Clostridium difficile
C. Yersinia enterocolitica
D. Salmonella

(Scroll down for the answer)

The answer is B. The photograph above shows pseudomembranous colitis, a condition caused by C. difficile infection, or “C. diff” for short. C. difficile colitis is also known as antibiotic-associated diarrhea, because it often colonizes a patient after antibiotic treatment wreaks havoc on the patient’s normal gut flora, making the way for this resilient bug. Toxins released by the bacteria result in compromise of the mucosa and apoptosis of the epithelial cells.

How is a “pseudomembrane” different from a real membrane, you might ask? While a “real” membrane is a thin layer of tissue overlaying or dividing some other tissue, the pseudomembrane here is just a layer of junk sitting on top of the colonic mucosa, and is composed of sloughed-off epithelial cells, neutrophils, and cellular debris. When enough of this stuff accumulates, it makes a sheet which covers most of mucosal surface of the colon and looks like a membrane.

The histology of C. diff is some of the most exciting in gastrointestinal pathology, because the neutrophils tend to “erupt” from the crypts, leading to the description “volcano crypts.” Needless to say, it is never a good thing when inflammatory cells are spilling from the colonic crypts like lava.

Who is at risk for C. diff? Risk factors include a compromised immune system, extended antibiotic treatment, and even just hospitalization, since C. diff is really easy to transfer from patient to patient. In fact, up to 30% of all hospitalized adults may be colonized with C. diff! Despite this, most carriers are asymptomatic.

When C. diff does cause problems, patients present with a characteristic watery diarrhea, which may be accompanied by fever, increased white blood count, crampy pain, and dehydration (from all the diarrhea). Bloody diarrhea is uncommon, which can help in ruling out other nasty bugs like Shigella and some types of E. coli, which do cause bloody diarrhea.

How do we detect C. diff in the lab? The most effective way is to detect the bacterial toxin in the stool. Standard treatments include metronidazole, with vancomycin for severe cases, but some strains are developing resistance even to that. Reinfection is also common. The bacteria are resistant to alcohol-based hand sanitizers, so anyone in contact with patients must wash their hands with soap and water, old-school style. Some patients with hard-to-treat C. diff have benefited from fecal transplant, which is a win-win situation for all parties involved!

* A huge thanks to Michelle Stoffel, MD PhD, PGY2 Pathology Resident at the University of Wisconsin, for yet another great case and informative, easy-to-read post! (Check out her other awesome case here.)

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