They are believed to be able to detect various volatile organic compounds released during various metabolic processes in the body, including those resulting from bacterial, viral and parasitic infections. coincide.
Preliminary data show that
Dogs can be trained to detect samples from COVID-19 patients within weeks, with a level of accuracy comparable to that of a standard PCR test.
.
Although promising, these laboratory data results need to be replicated under real-world conditions. Therefore, the researchers trained four dogs to sniff out SARS-CoV-2 in the spring of 2020. Each dog had previously been trained to sniff out illegal drugs, dangerous goods, or cancer.
Dogs can identify COVID-19 patients
To test the detection ability of the dogs,
420 volunteers each provided four swab samples. Each of the four dogs had skin samples sniffed from 114 volunteers who tested positive for SARS-CoV-2 in the PCR swab test and from 306 who tested negative.
Samples were randomly presented to each dog for seven trials.
Overall, the diagnostic accuracy for all sniffed samples was 92%: combined sensitivity (accuracy in detecting people with COVID-19) and specificity (accuracy in detecting COVID-19 patients). currently people who do not have COVID-19) are 92% and 91%, respectively.
Only slight differences were observed between dogs: the best performance was 93% in sensitivity and 95% in specificity; The lowest had a sensitivity of 88% and a specificity of 90%. These dogs identified passengers with COVID-19 faster than any other test.
About 28 of the positive samples came from people without symptoms. Only one was incorrectly identified as negative and two were not sniffed, meaning that 25 out of 28 animals (just over 89%) were correctly identified as positive: lack of symptoms appeared. Does not affect the activity of the dog.
The four dogs then went to work sniffing 303 incoming passengers at Helsinki-Vantaa International Airport, Finland, between September 2020 and April 2021.
Each passenger must also undergo a PCR swab test.
PCR and sniffer results matched 296 out of 303 (98%) real samples. Dogs correctly identified samples as negative in 296 of 300 (99%) PCR-negative swab tests and identified 3 PCR-positive cases as negative.
After reevaluation with clinical and serological data, one person is considered negative for SARS-CoV-2, another is positive for SARS-CoV-2, and one result may be positive. with post-infection PCR.
Similarly, dogs that indicated four negative PCR cases were positive. All of these people were assessed as negative for SARS-CoV-2 or without any cases of COVID-19.
Because the prevalence of SARS-CoV-2 among passengers at the airport was relatively low (less than 0.5%), 155 samples from people who tested positive for PCR were also given to dogs.
The dogs were correctly identified just under 99% of them as positive. If these “spike” samples were included in the real-life study, the performance of the dogs would reach a sensitivity of 97% and specificity of 99%.
Research based on obtained data
Based on these results, a study was performed and calculated the ratio of true positive results (PPV) and rate of true negative results (NPV) in two hypothetical scenarios reflecting The prevalence of SARS-CoV-2 in the population was 40% and 1%.
For a prevalence rate of 40%, they estimate a PPV of 88% and an NPV of 94.5%. This means that the information provided by sniffing dogs increases the likelihood of detection by about 90%.
On the other hand, for a population prevalence of 1%, they estimated a PPV of just under 10% and an NPV of less than 100%.
In both cases, the researchers say the high NPV supports the use of sniffer dogs for detection, with the goal of excluding those who do not need PCR testing.
And they suggest that “dogs can be used both in locations with high SARS-CoV-2 prevalence, such as hospitals (for pre-screening patients and staff), as well as in locations with low infection rates, such as airports or harbors (for pre-screening of passengers).” They say this will significantly save time and resources on passenger detection infected with COVID-19 in the airport.
The researchers acknowledge that the sniffer dogs also detect other substances that could misidentify these as positive for SARS-CoV-2. They say that the required storage time of the training and the spiked samples can also affect the viability of volatile organic compounds.
An important finding is
Sniff dogs were less successful at correctly identifying the alpha variant (COVID-19 infection), as they had been trained to detect the wild type
. But the researchers say that this identification only shows how good the dogs are at distinguishing between different scents.
“This observation is remarkable because it demonstrates the powerful discriminatory power of scent-bearing dogs. The implication is clear that training samples must include all epidemiologically relevant variations. . Our preliminary observations show that dogs injected with a virus can be retrained to detect within hours of its variants.”
Source: Medindia
