Monday, May 30, 2016

Identifying infections by their stench?

Bacteria tend to smell. A classic example is the geosmin-producing Streptomyces species responsible for the nice earthy scent of freshly dug up soil. In general, though, bacteria have unpleasant odours: Just think of cheese, armpits, and poop. Some of the stinkiest bacteria are ones capable of infecting us. The distinctiveness of their disgusting bouquets may provide a means of identifying them. Hippocrates apparently diagnosed tuberculosis (caused by the bacterium Mycobacterium tuberculosis) based on the particularly nasty odour produced by pouring gunk coughed up by an infected patient onto hot coals. Yuck.

Various strains of stinky Clostridium difficile (Source)

Clostridium difficile is the bane of hospitals all over the world. This bacterium tends to infect the intestines of people who have been on certain antibiotics. The antibiotics clear out a large chunk of the bacteria normally inhabiting a person's intestines, allowing C. diff (as it's called) to establish a foothold. The bacterium pumps out toxins which cause damage and disrupt the proper movement of food through the intestines (read: lots of diarrhea). In some cases, the large intestine can become super inflamed, a potentially life-threatening situation. If your guts become filled with C. diff, your poop tends to become watery (snot-like) and smell really bad in a distinctive way. It's commonly described in the scientific literature as an odour similar to horse manure, although a quick search through nursing forum threads such as this one mention, among other things, mouldy bread with a dash of skunk, a hot outhouse, rotting chicken, and a fart mixed with hot decaying roadkill.

Although the specific stench of a C. diff poop is reportedly difficult to miss, the one blinded study I found reported a group of 18 nurses were unable to identify poops from patients with C. diff infections based on their odour. That's not a particularly large sample group though, so it might be useful to do another study with more nurses to confirm these results.


Bartlett JG, Gerding DN. 2008. Clinical recognition and diagnosis of Clostridium difficile infection. Clinical Infectious Diseases 46(Supplement 1):S12-S18. [Full text]

Rao K, Berland D, Young C, Walk ST, Newton DW. 2013. The nose knows not: Poor predictive value of stool sample odor for detection of Clostridium difficile. Clinical Infectious Diseases 56(4):615-616. [Full text]

Sethi S, Nanda R, Chakraborty T. 2013. Clinical application of volatile organic compound analysis for detecting infectious diseases. Clinical Microbiology Reviews 26(3):462-475. [Full text]

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