According to a study published in the BMJ Global Health Journal, trained sniffer dogs can accurately identify airport passengers infected with SARS-CoV-2, the virus that causes COVID-19. This method of detection can be valuable, not only in the early stages of an epidemic when other resources may not yet be available, but also to help contain an ongoing epidemic, the researchers said.
One key finding was that dogs were less successful in identifying the alpha variant because they were trained to identify wild species. It just shows how good dogs are at distinguishing between different scents, they say Dogs are thought to be able to detect individual volatile organic compounds released during various metabolic processes in the body, including those produced by bacteria, viruses and parasites. Infection
Researchers at the University of Helsinki and the University of Helsinki Hospital in Finland trained four dogs in 2020 to sniff SARS-CoV-2. Each dog was previously trained to sniff out illicit drugs or dangerous products or cancer. To test the dog’s detection skills, 420 volunteers each provided four skin swab samples.
The four dogs each sniffed skin samples from 114 volunteers who tested positive for SARS-CoV-2 in the PCR swab test, and 306 who tested negative. Samples were randomly presented to each dog in seven trial sessions. The diagnostic accuracy of all sniffed samples was 92 percent: the combined sensitivity – the accuracy of identifying infected people – was 92 percent and the combined specificity – the accuracy of detecting without infection – was 91 percent.
Some of the 26 positive samples came from people who had no symptoms, the researchers said. Only one was incorrectly marked as negative and two were not sniffed, meaning that 25 out of 28 (more than 89 percent) were correctly marked as positive. : Lack of symptoms doesn’t seem to affect dog performance, they say.
Four dogs were then used to sniff out 303 passengers arriving at Helsinki-Vantaa International Airport in Finland between September 2020 and April 2021. A PCR swab test was also performed on each passenger. PCR and sniffer results matched 296 out of 303 (98 percent) real-life samples. The dogs accurately identified the sample as negative in 296 of the 300 (99 percent) PCR-negative swab tests and identified three PCR-positive cases as negative, the researchers said.
After re-evaluation with clinical and serological data, one was judged to be SARS-CoV-2 negative, one SARS-CoV-2 positive and one possibly post-infectious positive PCR test result, they said. Similarly, the dogs indicated four PCR negative cases as positive. These were judged to be SARS-CoV-2 negative. Because the prevalence of SARS-CoV-2 among airport passengers was relatively low (less than 0.5 percent), 155 samples from people who tested positive in the PCR swab test were also presented to dogs.
Dogs correctly identified positive as below 99 percent of them If these ‘spike’ samples had been included in real-life studies, dogs’ performance would have reached a sensitivity of 97 percent and a specificity of 99 percent, the researchers said.
Based on these results, they calculated the ratio of True Positive Outcome (PPV) and True Negative Outcome (NPV) in two hypothetical situations, reflecting the population prevalence of SARS-CoV-2 at 40 percent and 1 percent. Outbreaks of 40 percent, they estimated PPV at 88 percent and NPV at 94.5 percent This means that the information provided by the dog increases the probability of detection by about 90 percent Population trends are 1 percent, on the other hand, they estimate PPV is just under 10 percent and an NPV is just under 100 percent.
In both cases, high NPV supports the use of sniffer dogs for screening, with the aim of excluding people who do not require PCR swab testing, the researchers said. “Dogs can be used in both high prevalence of SARS-CoV-2, such as in hospitals (for prescribing patients and staff), as well as in low-trend sites, such as airports or ports (for prescribing passengers),” they said. .
Researchers have acknowledged that dogs trained to sniff out other substances may mistakenly identify these substances as SARS-CoV-2 positive. The required storage duration of training and spiked samples can affect the effectiveness of volatile organic compounds, they said.