Biomedical detection dogs for the identification of SARS-CoV-2 infections from axillary sweat and breath samples ^**

Abstract

A PCR test of a nasal swab is still the “gold standard” for detecting a SARS-CoV-2 infection. However, PCR testing could be usefully complemented by non-invasive, fast, reliable, cheap methods for detecting infected individuals in busy areas (e.g. airports and railway stations) or remote areas. Detection of the volatile, semivolatile and non-volatile compound signature of SARS-CoV-2 infection by trained sniffer dogs might meet these requirements. Previous studies have shown that well-trained dogs can detect SARS-CoV-2 in sweat, saliva and urine samples. The objective of the present study was to assess the performance of dogs trained to detect the presence of SARS-CoV-2 in axillary-sweat-stained gauzes and on expired breath trapped in surgical masks. The samples were provided by individuals suffering from mild-to-severe coronavirus disease 2019 (COVID-19), asymptomatic individuals, and individuals vaccinated against COVID-19. Results: Seven trained dogs tested on 886 presentations of sweat samples from 241 subjects and detected SARS-CoV-2 with a diagnostic sensitivity (relative to the PCR test result) of 89.6% (95% confidence interval (CI): 86.4-92.2%) and a specificity of 83.9% (95% CI: 80.3-87.0%) - even when people with a low viral load were included in the analysis. When considering the 207 presentations of sweat samples from vaccinated individuals, the sensitivity and specificity were respectively 85.7% (95% CI: 68.5-94.3) and 86.0% (95% CI: 80.2-90.3%). The likelihood of a false-positive result was greater in the two weeks immediately after COVID-19 vaccination. Four of the seven dogs also tested on 262 presentations of mask samples from 98 subjects; the diagnostic sensitivity was 83.1% (95% CI: 73.2-89.9) and the specificity was 88.6% (95% CI: 83.3-92.4%). There was no difference (McNemar's test P=0.999) in the dogs’ abilities to detect the presence of SARS-CoV-2 in paired samples of sweat-stained gauzes vs. surgical masks worn for only 10 minutes. Conclusion: Our findings confirm the promise of SARS-CoV-2 screening by detection dogs and broaden the method’s scope to vaccinated individuals and easy-to-obtain face masks, and suggest that a “dogs + confirmatory rapid antigen detection tests” screening strategy might be worth investigating.

Expert considerations and consensus for using dogs to detect human SARS-CoV-2-infections

“…Indeed, a varying collection period was applied depending on the body region across the reviewed COVID-19-detection studies. While a short swabbing of the crook of the arm, wrist, face or neck was sufficient for high diagnostic accuracies with sensitivities and specificities above 91% in three studies (69,70,134), studies that used axillary sweat or other sweat type chose a longer collection period of around 1-20 min (51,117,(184)(185)(186)(187)(188)(189)(190)(191)(192) or even periods of hours in case of clothes (47, 144). However, in most cases these periods were arbitrarily chosen (4).…”

“…For example, Gokool et al provided preliminary evidence that the specific odor persists for months in worn cotton shirts ( 193 ). Sweat samples for COVID-19-detection were stored cooled or at room temperature for around 2 h ( 194 ), 24–72 h ( 70 , 185 – 187 , 189 , 190 , 192 ), 1 week ( 188 ), or even up to 6 months in triple zip-lock plastic bags ( 69 ) before being presented to a dog. In some studies, sweat samples (and clothes) were frozen and then presented to the dogs thawed after longer storage periods in order to preserve VOCs ( 47 , 52 , 117 , 134 , 191 ).…”

Canine real-time detection of SARS-CoV-2 infections in the context of a mass screening event

“…Several studies have shown the ability of medical scent detection dogs to identify samples from SARS-CoV-2 infected individuals with high accuracy, highlighting the role such dogs could play in the management of a pandemic 1–13. Previous research showed that different body fluids, such as saliva, sweat and urine and other sample types like worn face masks are suitable for detection, which suggests that there is a general SARS-CoV-2 infection associated odour that dogs can be trained on 14–16. In addition, our group demonstrated that such dogs were able to differentiate SARS-CoV-2 infection from other acute viral respiratory tract infections 17.…”

“…BMJ Global Health which suggests that there is a general SARS-CoV-2 infection associated odour that dogs can be trained on. [14][15][16] In addition, our group demonstrated that such dogs were able to differentiate SARS-CoV-2 infection from other acute viral respiratory tract infections. 17 However, most of the current data were generated in laboratory settings, rather than in a real-world scenario or lacked the verification of SARS-CoV-2 infections by a PoC-antigen test and real-time quantitative reverse transcription-PCR (RT-qPCR).…”

“…In several studies, dogs demonstrated their capability to distinguish SARS-CoV-2 RT-qPCR positive samples from RT-qPCR negative samples with high diagnostic accuracy regardless of training method or sample type 1–18 31 32. However, most studies were conducted under laboratory conditions with a small number of samples and high artificial prevalences.…”