Scent-detecting dogs have long been used to sniff out medical conditions ranging from low blood sugar and cancer to malaria, impending seizures, and migraines – not to mention explosives and narcotics.
Recently, the sensitivity of the canine nose has been tested as a strategy for screening for SARS-CoV-2 infection in schoolchildren showing no outward symptoms of the virus. A pilot study led by Carol A. Glaser, DVM, MD, of the California Department of Public Health in Richmond, found that trained dogs had an accuracy of more than 95% for detecting the odor of volatile organic compounds, or VOCs, produced by COVID-infected individuals.
The authors believe that odor-based diagnosis with dogs could eventually provide a rapid, inexpensive, and noninvasive way to screen large groups for COVID-19 without the need for antigen testing.
“This is a new program with research ongoing, so it would be premature to consider it from a consumer’s perspective,” Dr. Glaser said in an interview. “However, the data look promising and we are hopeful we can continue to pilot various programs in various settings to see where, and if, dogs can be used for biomedical detection.”
In the lab and in the field
In a study published online in, Dr. Glaser’s group found that after 2 months’ training on COVID-19 scent samples in the laboratory, the dogs detected the presence of the virus more than 95% of the time. Antigen tests were used as a comparative reference.
In medical terms, the dogs achieved a greater than 95% accuracy on two important measures of effectiveness: sensitivity – a test’s ability to correctly detect the positive presence of disease – and specificity – the ability of a test to accurately rule out the presence of disease and identify as negative an uninfected person.
Next, the researchers piloted field tests in 50 visits at 27 schools from April 1 to May 25, 2022, to compare dogs’ detection ability with that of standard laboratory antigen testing. Participants in the completely voluntary screening numbered 1,558 and ranged in age from 9 to 17 years. Of these, 56% were girls and 89% were students. Almost 70% were screened at least twice.
Overall, the field test compared 3,897 paired antigen-vs.-dog screenings. The dogs accurately signaled the presence of 85 infections and ruled out 3,411 infections, for an overall accuracy of 90%. In 383 cases, however, they inaccurately signaled the presence of infection (false positives) and missed 18 actual infections (false negatives). That translated to a sensitivity in the field of 83%, considerably lower than that of their lab performance.
Direct screening of individuals with dogs outside of the lab involved circumstantial factors that likely contributed to decreased sensitivity and specificity, the authors acknowledged. These included such distractions as noise and the presence of excitable young children as well environmental conditions such as wind and other odors. What about dog phobia and dog hair allergy? “Dog screening takes only a few seconds per student and the dogs do not generally touch the participant as they run a line and sniff at ankles,” Dr. Glaser explained.
As for allergies, the rapid, ankle-level screening occurred in outdoor settings. “The chance of allergies is very low. This would be similar to someone who is out walking on the sidewalk and walks by a dog,” Dr. Glaser said.
Last year, aof almost 4,000 adults tested six dogs trained to detect differences in VOCs between COVID-infected and uninfected individuals. Given samples from both groups, the dogs were able to distinguish between infected and uninfected samples with a sensitivity for detecting the virus ranging from 82% to 94% and a specificity for ruling it out of 76% to 92%. And they were able to smell the VOCs even when the viral load was low. The study also tested organic sensors, which proved even more accurate than the canines.
According to lead author James G. Logan, PhD, a disease control expert at the London School of Hygiene & Tropical Medicine in London, “Odour-based diagnostics using dogs and/or sensors may prove a rapid and effective tool for screening large numbers of people. Mathematical modelling suggests that dog screening plus a confirmatory PCR test could detect up to 89% of SARS-CoV-2 infections, averting up to 2.2 times as much transmission compared to isolation of symptomatic individuals only.”
Funding was provided by the Centers for Disease Control and Prevention Foundation (CDCF) to Early Alert Canines for the purchase and care of the dogs and the support of the handlers and trainers. The CDCF had no other role in the study. Coauthor Carol A. Edwards of Early Alert Canines reported receiving grants from the CDCF.