Dogs sniff out COVID-19 with high accuracy, study shows

In a recent study published in the Annals of Epidemiology, researchers conducted a systematic review to determine the potential of using canine olfactory senses as a screening tool for the coronavirus disease 2019 (COVID-19).

Study: Canine Olfactory Detection of SARSCoV2Infected Humans – a Systematic Review. Image Credit: Luminoisty-images.com / Shutterstock.com

Background

The COVID-19 pandemic, caused by the emergence of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), resulted in unprecedented cases and deaths worldwide.

The pandemic has also significantly impacted the economic, psychological, political, and cultural aspects of life. The various non-pharmaceutical disease mitigation measures implemented during the pandemic, such as lockdowns in various countries and social distancing measures, have also influenced mental health levels worldwide.

Nevertheless, the pandemic also led to the rapid development of diagnostic and vaccine technologies, with antigen tests and quantitative reverse transcription polymerase chain reaction (qRT-PCR) being employed to screen individuals for COVID-19. While the significant advancements in vaccine technology have been successful in limiting the severity of SARS-CoV-2 infections, the evolution and emergence of the highly evasive Omicron variant and its sub-variants indicate that a combination of pharmaceutical and non-pharmaceutical measures are needed as the COVID-19 pandemic continues to evolve.

About the study

In the present study, researchers investigate the potential for using canine olfactory senses to screen for SARS-CoV-2 infection. Canine olfactory senses are acute and have been utilized for various purposes, including guarding, hunting, and detecting substances and life forms.

Some diseases cause organic compounds to be released that can be detected by the highly sensitive olfactory senses of dogs. This has been used to train dogs to detect hypoglycemia in individuals with diabetes mellitus, epileptic seizures, malaria, cancer, and the presence of Clostridium difficile in fecal samples and Staphylococcus aureus, Escherichia coli, Klebsiella, and Enterococcus in urine samples.

The detection of specific volatile organic compound profiles by dogs to identify diseases provides a rapid and high-throughput disease detection option as compared to conventional approaches. If the dogs are fit-for-purpose and can provide accurate results, they can be used to screen large groups of people before individual tests are administered to confirm infection.

The present systematic review assessed various studies and summarized the findings on the use of dogs to screen for SARS-CoV-2 infections. Two evaluation systems were used to assess the evidence on the fitness-for-purpose of using detection dogs for COVID-19 screening.

The Quality Assessment of Diagnostic Accuracy Studies 2 (QUADAS-2) system evaluates the applicability of the diagnostic accuracy study and risk bias, whereas the other evaluation system examines canine medical scent detection.

Publications that included a study population of SARS-CoV-2-infected individuals or biological samples from individuals with SARS-CoV-2 infection, an intervention or index test consisting of canines or Canis lupus familiaris, and a reference standard or control consisting of samples subjected to PCR testing were included in the review. The examined outcomes included diagnostic sensitivity, accuracy, and specificity.

Results

In the current review, 27 studies from 13 countries were evaluated. Of these studies, QUADAS-2 and the other evaluation system selected four and six studies, respectively, which have high quality and low bias risk.

Canis lupus familiaris could detect, with high specificity and sensitivity, SARS-CoV-2 infections from individuals or biological material.

The specificity and sensitivity ranges of the four studies selected by the QUADAS-2 system were 91% to 100% and 81% to 97%, respectively. Similarly, the specificity and sensitivity ranges of the six studies selected by the general evaluation system were 83% to 100% and 82% to 97%, respectively. Other studies have also reported that canine detection can outperform standard PCR tests with higher specificity.

However, the applicability of dogs to detect SARS-CoV-2 infections and bias risk continue to present concerns. During diagnostic test evaluation, the novelty of the samples and omission of repetition of samples is essential to help dogs distinguish between a generalized COVID-19 odor profile and personal odor profiles of individuals.

Furthermore, since dogs are living beings with varying personalities and behaviors, positive reinforcement during training is an ethical necessity. Additionally, the physiology of the dog and factors such as sex, age, and mental condition can influence the scent work and the olfactory senses.

Conclusions

The study findings indicate that dogs can detect SARS-CoV-2 infections from humans and biological samples with high specificity and sensitivity.

However, procedures to standardize and certify the dogs and ensure the accuracy of the results are essential. Furthermore, the guidelines and legal frameworks that have been used to train dogs to detect explosives should be employed to construct similar guidelines for dogs that detect medical scents.