Odors and Infections

Many illnesses are associated with distinct odors. Especially those caused by infectious or opportunistic microbes inside the body or on its surfaces.  Body odor of someone infected with C. difficile, for example, can appear "swampy", Rotavirus gives sharply sweet putrid smell that some people associate with wet dogs. H. pylori can create a range of foul odors, and pseudomonas infections can smell like grapes and bitter almonds. 

Infections like C. difficile are usually linked to a general imbalance of the intestinal microbiota, often referred to as dysbiosis. This means that the odors could be coming from several microbial species, hence could be different for different individuals. Does it mean odor-based diagnostics will never be enough specific?

Not according to a 2-year-old beagle from Netherland, named Cliff. After just a little over two months of training, the beagle learned to identify the C. diff toxin by sniffing people or their samples. During one test, he was able to identify 25 out of 30 infected patients and 265 of 270 non-infected individuals. He also correctly identified 50 of 50 C. diff positive stool samples and 47 of 50 samples from people that did not have this infection. That's sensitivity of 100% for samples and 83-93% for sniffing the air around the patients, and a specificity of 94-100%! And it took him less than 10 minutes to accurately perform 300 diagnostic tests.  

Dogs already do the dirty work with detecting molds. They can examine an office building with 200 rooms in just 8 hours, a task that would take us several days of measuring  moisture, probably without any result. Electronic noses would be of great help and many years of research are finally being translated into useful technologies - to be integrated with refrigerators and mobile phones. But until we are able to build smart devices to detect odors without labor-intensive dog training, perhaps we could train our own nozzles. Studies have shown we do get better with practice. 


REFERENCES

Bomers MK, van Agtmael MA, Luik H, van Veen MC, Vandenbroucke-Grauls CM, & Smulders YM (2012). Using a dog's superior olfactory sensitivity to identify Clostridium difficile in stools and patients: proof of principle study. BMJ (Clinical research ed.), 345 PMID: 23241268

Poulton J, Tarlow MJ. (1987) Diagnosis of rotavirus gastroenteritis by smell. Arch Dis Child. 1987 Aug;62(8):851-2. PMID: 3662595

Arnaud Tognetti, Megan N Williams, Nathalie Lybert, Mats Lekander, John Axelsson, Mats J Olsson, Humans can detect axillary odor cues of an acute respiratory infection in others, Evolution, Medicine, and Public Health, Volume 11, Issue 1, 2023, Pages 219–228, https://doi.org/10.1093/emph/eoad016