Breath testing is a fast, non-invasive method that is based on the presence of specific volatile organic compounds (VOCs) in exhaled breath:
- human breath contains more than three thousand different compounds including large number of volatile organic compounds (VOCs)
- exhaled VOCs may originate from two main sources: exogenous volatiles that are present in sampling material or inhaled (or absorbed through the skin) and then exhaled and those endogenously produced by different biochemical processes including those that are released during cancer cell metabolism
- there are several lines of evidence showing that metabolic pathways in cancer cells produce different volatile compounds (or at least a different pattern of them) than in noncancerous tissue. These effects have been observed in a variety of different cancer types including lung, breast and malignant melanomas.
- the wide variety of confounding sources makes the application of standardised breath sampling and analysis critically important (1,2)
Canine based sensing of 'smellprints' have also been applied:
- dogs and smelling cancerous lesions:
- dogs had an accuracy of 99% in discriminating between smells from exhaled breath of patients with lung cancer and controls. The stage of cancer, age of patients, smoking habit or the most recently eaten meal did not influence the dog’s diagnostic performance (3)
- dogs and smelling infections:
- studies have proven the canines' acuity to detect persons with malaria (4), bacterial, and viral infections (5,6)
- with respect to detection of viruses - compared to bacteria, viruses have no own metabolism, and therefore VOCs are released by infected body cells as a result of metabolic host processes rather than related to the virus itself
- in a study related to the detection of COVID-19 (SARS-CoV-2) (7)
- 8 detection dogs were trained for 1 week to detect saliva or tracheobronchial secretions of SARS-CoV-2 infected patients in a randomised, double-blinded and controlled study
- dogs were able to discriminate between samples of infected (positive) and non-infected (negative) individuals with average diagnostic sensitivity of 82.63% (95% confidence interval [CI]: 82.02-83.24%) and specificity of 96.35% (95% CI: 96.31-96.39%). During the presentation of 1012 randomised samples, the dogs achieved an overall average detection rate of 94% (+/-3.4%) with 157 correct indications of positive, 792 correct rejections of negative, 33 incorrect indications of negative or incorrect rejections of 30 positive sample presentations
- the study authors concluded that preliminary findings indicate that trained detection dogs can identify respiratory secretion samples from hospitalised and clinically diseased SARS-CoV-2 infected individuals by discriminating between samples from SARS-CoV-2 infected patients and negative controls
Reference:
- (1) Horváth I, Lázár Z, Gyulai N, Kollai M, Losonczy G. Exhaled biomarkers in lung cancer. Eur Respir J 2009;34:261-75.
- (2) Szulejko JE, McCulloch M, Jackson J, McKee DL, Walker JC, Solouki T. Evidence for cancer biomarkers in exhaled breath. IEEE Sensors J 2010;10:185-210.
- (3) Editorial. Lung cancer. Lung Cancer 2010;68: 127-128.
- (4) Guest C et al. Trained dogs identify people with malaria parasites by their odour. Lancet Infect Dis. 2019 Jun; 19(6):578-580
- (5) Taylor MT et al. Using Dog Scent Detection as a Point-of-Care Tool to Identify Toxigenic Clostridium difficile in Stool.Open Forum Infect Dis. 2018 Aug; 5(8):ofy179.
- (6) Angle TC et al. Real-time detection of a virus using detection dogs. Front. Vet. Sci. 2016;2:1-6. doi: 10.3389/fvets.2015.00079
- (7) Jendmy P et al. Scent dog identification of samples from COVID-19 patients - a pilot study. BMC Infect Dis. 2020; 20: 536.