There are numerous articles out there that dogs are being trained out to sniff out COVID-19, specifically the smells that are given off by the infected as COVID-19 doesn’t have an odor. In some cases, they are also being trained to sniff out COVID-19 smells from infected people in saliva samples. Here are several examples – https://www.smithsonianmag.com/smart-news/helsinki-airport-employs-dogs-sniff-out-signs-covid-19-travelers-sweat-180975923/; https://www.darkdaily.com/german-scientists-train-dogs-to-detect-the-presence-of-covid-19-in-saliva-samples-can-a-canines-nose-be-as-accurate-as-clinical-laboratory-testing/. In the second link, dogs were able to detect COVID-19 infected individuals from saliva samples 94% of the time. Some dogs reach 100% rate from sweat samples. That’s pretty impressive either way. I know with the sweat samples, the dogs were sniffing several containers, only one of which had a sweat sample. The advantage is the dogs may detect a COVID-19 individual before the person realizes they have it. The smells are given off
This could be a great way to test large numbers of people without having to wait for lab results. According to this article – https://slate.com/technology/2020/08/covid-19-sniffing-dogs.html, it’s the “volatile organic compounds” given off. Different conditions give off specific “volatile organic compounds” and you could use separate dogs trained to recognize each disease. There are some other issues mentioned in this article that could come into play.