Background: Sniffer dogs have been shown to detect certain chemical particles and to help diagnose many diseases and complications, such as colorectal cancer, melanoma, bladder cancer, and even dangerous states such as hypoglycemia in DM-1 patients. With the spread of COVID-19 throughout the world and the need to have a real-time screening of the population, especially in crowded places, this study aimed to investigate the applicability of these sniffer dogs.
Methods: This study was done in two phases. In the first step, three dogs (including one German shepherd, one German black, one Labrador) were intensively trained by the classical conditioning method for seven weeks. Human specimens were obtained from the throat culture and pharyngeal secretions of both definitely positive and negative COVID-19 participants. During the first seven weeks, each dog underwent the conditioning process for averagely 1000 times. In the verification process, 80 pharyngeal secretion samples consisting of 26 positive samples of hospitalized patients and 54 negative samples of hospitalized patients for other medical reasons were provided to the training team in a single-blind manner. The verification test was done using three dogs (Lexi, Sami, and Kozhi). Another similar conditioning process was done using COVID-19 patients’ clothes and masks and the verification test was done using 50 positive and 70 negative samples by three other trained dogs (one Labrador, one Border gypsy, and one Golden retriever).
Results: In the pharyngeal secretions verification test, the sniffer dogs showed 65% sensitivity and 89% specificity. In this process, they could identify 17 out of the 26 true positive samples and 48 out of the 54 true negative samples. According to the results, the positive predictive value and negative predictive value for this experiment were 74% and 84%, respectively. In the next verification test for the patients’ face masks and clothes, 43 out of the 50 positive samples were correctly identified by the dogs. Moreover, out of the 70 negative samples, 65 samples were correctly found to be negative by the canines. The sensitivity of this method was as high as 86% and its specificity was 92.9%. In addition, the positive and negative predictive values were 89.6% and 90.3%, respectively.
Conclusion: Dogs are capable of being trained as the identifier of people with COVID-19 by detecting their odor and can be used as a reliable tool in limited screening.