A new novel coronavirus saliva detection technique that is more accurate and easier than nasal swabs
Since the outbreak of the epidemic, the detection technology of novel coronavirus has made rapid progress. However, at that time, people had to go to the hospital for a nasal swab test that was deep enough to “make the brain itch”, and waited for several days to get the results. Now, the University of Illinois at Urbana Champaign (UIUC), Yale University, Rockefeller University and other universities have independently developed a series of saliva based detection technologies. These tests are less invasive, faster to process, and in some cases more sensitive than nasal tests.
“Although nasal swabs may not be practical in daily use, it is quite easy to provide saliva samples repeatedly,” said Rebecca Lee Smith. He is the infectious disease epidemiologist of UIUC and the scientific adviser of covidshield project, which is the nucleic acid detection project conducted by Brennan.
Covidshield is a polymerase chain reaction (PCR) detection, which is a highly sensitive molecular detection method. It can amplify the genetic material of sars-cov-2 (a novel coronavirus causing covid) to a detectable level. PCR analysis is usually performed in the laboratory, but not all.
After the covidshield saliva sample is delivered to the laboratory, the scientists will put it into a hot tub to kill any existing virus and neutralize saliva components that may interfere with the detection. Then the sample can be amplified. First, “primers” (short fragments of genetic material) are added to the sample. As Smith explained, primers are “a little ‘idea’ of the virus at the RNA [genetic material] level”. RNA from the virus is converted into complementary DNA (cDNA). Finally, the primer will connect itself to the cDNA of the virus and replicate. As this process continues, all cDNAs will be continuously amplified until positive samples can be easily identified and detected.
Covidshield’s method discards the traditional RNA extraction step and uses heating and chemical treatment to release viral RNA. This enables test developers to promise to provide test results within 24 hours. According to Beth Heller, a spokeswoman for shield Illinois, a nonprofit Department of the University of Illinois system, the average turnaround time can be even shorter. “From sample collection to providing test results, we now spend an average of 13 hours,” Beth Heller said.
The time difference between receiving the coronal test and obtaining the results is a key indicator to evaluate the diagnostic method. In addition to the sensitivity of the overall detection, this is also part of the extensive debate about the use of PCR and rapid antigen detection. Antigen detection is mainly based on nasal swabs, although researchers are working to develop an accurate version based on saliva. Antigen detection is to detect the presence of viral antigens by using a special test paper, and viral antigens are viral fragments that cause immune reactions.
Proponents of antigen testing believe that its advantages of speed and low cost make it more suitable as a public health tool. Epidemiologist Michael Mina believes that PCR testing should really be reserved for medical research, especially those tests that must be sent to the laboratory, and should not be used, for example, when doctors diagnose patients. She is currently the chief scientific officer of emed, and has also provided testing advice to US President Joe Biden and his government. The antigen testing methods sold by the company have been certified through the telemedicine platform.
The hypersensitivity of PCR detection is one of the main problems in public health. Mina said: “I don’t want someone to test positive when they are no longer infectious, because if they are positive, I will tell them that they will be isolated for 10 days; if they are no longer infectious and are isolated for 10 days, it will be harmful to public health.”
However, Smith believes that saliva based PCR detection and antigen detection are very different in use cases. Her research team provided the Centers for Disease Control and prevention with strategies on how to use antigen testing. “Saliva based PCR tests are very sensitive and they can actually detect infection before you get infected,” Smith said They are as sensitive or even more sensitive as PCR detection of nasal swabs. This may be particularly effective for the Omicron variant because it replicates more in the mouth and throat than the previous variant.
Smith explained that even if someone is no longer infectious, the PCR of his saliva may still show positive due to the sensitivity of the technology. At this point, antigen testing may be more appropriate to determine when someone is no longer infectious. She added: “I do not recommend any PCR (detection) for withdrawal from isolation, but antigen testing may be very useful in this regard.”
In the early stages of the pandemic, saliva based covid testing required recourse to healthcare professionals. But covidshield and other recently developed saliva testing technologies make testing easier. And this availability has also begun to extend to families: the US Food and Drug Administration (FDA) has approved several emergency use authorizations for self-collection and saliva based PCR testing technology, including a test using covidshield technology. “Self collection” refers to self collection of saliva without the presence of a trained observer. Although they still need to be transported to the laboratory for analysis, this avoids the need to go to the testing site and makes it possible to collect samples at home. According to David Clark, CEO of shield T3, a subsidiary of the University of Illinois systems, the company has recently started to produce covidshield self collection kits, which include all the materials needed to provide samples and send them to the laboratory for testing collection points. Clark said that shield T3 is currently providing kits to schools, universities and some companies on a limited basis. Eventually, he and his team envisioned distributing these kits through vending machines or in the workplace.