RESUMO
Facing the COVID-19 pandemic, testing individuals in order to promptly isolate positive people is one of the key actions. One approach to rapid testing might be to consider the olfactory capacities of trained detection dogs in order to develop a non-invasive, rapid and cheap mass detection approach, through the Volatile Organic Compounds (VOCs) signature of SARS-CoV-2 infection. The goal of this study was to determine the individual values of sensitivity and specificity of trained dogs when performing olfactory detection of COVID-19 on axillary sweat samples. Seven dogs were used to sniff a total of 218 samples (62 COVID-19 positive and 156 COVID-19 negative samples), based on a randomised and double-blinded protocol carried out on olfaction cone line-ups. To ensure a wide olfactory range as close as possible to operational conditions, the samples were retrieved from 13 different sites. Sensitivities varied from 87% to 94% for 6 dogs, and were above 90% for 3 of them. Only one dog, whose sensitivity was 60%, was not selected to subsequently enter the operational stage. Specificities varied from 78% to 92%, with 6 dogs over 85% and 4 dogs over 90%. Based on the calculated sensitivity and specificity for each dog, positive and negative predictive values (PPV and NPV) were calculated according to several prevalence rates of SARS-CoV-2 scenarii, and were compared to PPV and NPV of an "almost perfect" diagnostic tool. For 6 out of the 7 dogs, and for a prevalence rate of SARS-CoV-2 lower or equal than 40%, the NPV of the dogs were virtually the same as the one of the "almost perfect" tool. Along with other studies on olfactory detection of COVID-19 by dogs these positive and encouraging results suggest that olfactory dogs may play an important part in mass COVID-19 pre-testing situations.
RESUMO
This study aimed to evaluate the sensitivity of 21 dogs belonging to different United Arab Emirates (UAE) Ministry of Interior (MOI), trained for COVID-19 olfactory detection. The study involved 17 explosives detection dogs, two cadaver detection dogs and two dogs with no previous detection training. Training lasted two weeks before starting the validation protocol. Sequential five and seven-cone line-ups were used with axillary sweat samples from symptomatic COVID-19 individuals (SARS-CoV-2 PCR positive) and from asymptomatic COVID-19 negative individuals (SARS-CoV-2 PCR negative). A total of 1368 trials were performed during validation, including 151 positive and 110 negative samples. Each line-up had one positive sample and at least one negative sample. The dog had to mark the positive sample, randomly positioned behind one of the cones. The dog, handler and data recorder were blinded to the positive sample location. The calculated overall sensitivities were between 71% and 79% for three dogs, between83% and 87% for three other dogs, and equal to or higher than 90% for the remaining 15 dogs (more than two thirds of the 21 dogs). After calculating the overall sensitivity for each dog using all line-ups, "matched" sensitivities were calculated only including line-ups containing COVID-19 positive and negative samples strictly comparable on confounding factors such as diabetes, anosmia, asthma, fever, body pain, diarrhoea, sex, hospital, method of sweat collection and sampling duration. Most of the time, the sensitivities increased after matching. Pandemic conditions in the U.A.E., associated with the desire to use dogs as an efficient mass-pretesting tool has already led to the operational deployment of the study dogs. Future studies will focus on comparatives fields-test results including the impact of the main COVID-19 comorbidities and other respiratory tract infections.
