No worse than laboratory diagnostics

Dogs Detect COVID-19 with Greater Sensitivity Than Antigen Tests

Alina Suleymanova, PCR.news

French scientists have evaluated the effectiveness of detecting SARS-CoV-2 in humans by sniffing dogs.

Currently, coronavius is detected using antigenic or PCR tests. Both procedures require taking a smear from the nasopharynx, which can be associated with some difficulties for some groups of the population, for example, for children. In the case of a PCR test, it is necessary to transport the sample to the place of analysis, and this takes time. Previously, researchers hypothesized that the effect of SARS-CoV-2 on cells may be accompanied by the formation of volatile organic compounds, which are subsequently released from human sweat. It is these substances that dogs can smell.

The study was conducted within the framework of the SALICOV-APHP project dedicated to the search for new approaches to the diagnosis of COVID-19. Dogs from the French Fire Safety Service and the UAE Ministry of the Interior took part in the work. The dogs were trained according to the protocol developed earlier. The duration of training depended on the abilities and level of training of the dog and ranged from three to five to six weeks. During the study, the search for positive sweat samples was carried out in a specially designated room. Tampons soaked in sweat were placed in special metal cones. Dogs sniffed cones and gave a positive signal in case of detection of specific volatile substances (see illustration). The study was blinded: dog handlers did not know the coronavirus status of patients.

Scientists collected sweat samples from 335 patients. In addition, nasopharyngeal swabs and saliva samples were taken for a PCR test and a test for the SARS-CoV-2 antigen. The PCR test is considered the benchmark; its result was positive in 109 patients, including 78 with symptoms and 31 asymptomatic.

Four-legged participants gave a positive signal for 126 patients. 106 of them were also found positive according to the results of the PCR test. Dogs did not detect SARS-CoV-2 in 209 cases, 206 of which were also assessed as negative after PCR. The sensitivity of dogs was 97%, specificity — 91%. In relation to asymptomatic patients, the sensitivity of the dogs' sense of smell was 100%, and the specificity was 94%.

234 patients passed the SARS-CoV-2 antigen test. The authors note that the sensitivity of the canine sense of smell exceeded that for antigenic tests (97% vs. 84%), but the specificity was lower (90% vs. 97%).

Scientists also checked whether human infection with other viruses can affect the sense of smell of dogs. They tested 17 saliva samples from individuals with a negative PCR test, but recognized by dogs as infected, for other respiratory pathogens. Two samples contained other viruses, but it is important to note that these were the NL63 and OC43 coronaviruses.

Thus, dogs can be considered as a fast, non-invasive and fairly reliable screening method for SARS-CoV-2. Potentially, dogs would be a good solution for children or people with nervous system disorders, as well as for airports and other public places. As in the case of antigenic tests, positive results need to be confirmed by PCR analysis. The limitations of the method include the need for proper training and certification of animals and the fear of dogs in humans.

Article by Grandjean et al. Diagnostic accuracy of non-invasive detection of SARS-CoV-2 infection by canine olfaction is published in the journal PLoS ONE.

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