saliva based COVID-19 detection

The test, described in a preprint manuscript posted Friday on the online archive MedRxiv.org, is designed for widespread screening to help identify asymptomatic individuals. Research shows people infected with the virus but with no obvious symptoms make up as many as 70% of cases and can still spread disease. In this new test, a user spits in a tube, adds a solution to stabilize it then closes the lid and hands it off to testing staff. They process it through a simple system requiring little more than pipettes, a heating source and an enzyme mixture.

If the sample turns from pink to yellow, the test is positive. If it doesn't, it's negative.

"Every test that has been approved to date requires that the sample, even if it's saliva, be processed in a clinical diagnostic lab or at a doctor's office, using sophisticated equipment. That can take up to nine days right now," 

The test is based on a 20-year-old technology known as reverse transcription loop-mediated isothermal amplification (RT-LAMP) previously used, for instance, to screen mosquitoes for the Zika virus in remote regions of South America.

Once a sample is collected, it is heated to liberate any viral genome present in the test liquid. This sample is then added to three tubes, each containing a custom enzyme mixture which, when heated to a certain temperature, undergoes a chemical reaction when the genetic material from SARS-CoV-2 is detected. That's the virus that causes COVID-19.

The authors note that the test is slightly less sensitive than those performed in clinical labs

 

아래는 논문에서 발췌한 내용

The assay has a limit of detection of 100 virions per microliter

RT-LAMP is fast (typically < 1 hour from sample to result), robust to sample contaminants in crude specimen preparations, and requires no sophisticated equipment. RT-LAMP assays amplify nucleic acids at a constant temperature, requiring only inexpensive equipment that divorces them from clinical laboratories altogether

These assays 1) are specific because they employ four to six primers for each amplification reaction which in principle reduces off-target effects when compared to PCR, 2) are robust in that they can produce on the order of 10 to the power of 9 copies of the target in an hour-long reaction (Notomi et al., 2000), and 3) can be performed anywhere because they simply require pipettors and a heating source

 

Off target effect? 표적 유전자의 염기서열과 유사한 염기서열에도 변이를 일으킬 수 있다.

 

Protocol

 

reference

 Nicholas R. Meyerson et al. A community-deployable SARS-CoV-2 screening test using raw saliva with 45 minutes sample-to-results turnaround, (2020). DOI: 10.1101/2020.07.16.20150250