Most current tests for SARS-Cov-2 (the virus that causes the disease Covid19) are based on using a technique called PCR to look for genetic information specific to that virus, such as stretches of the genes it has for making proteins that it needs but we don’t have. There’s not much of this viral info, so scientists have to make lots of copies of it and use sensitive methods to detect it.

In PCR (Polymerase Chain Reaction), short pieces of DNA called primers are used to specify a region of the viral genome to copy. Fluorescent probes bind to the copies and let off light which allows scientists to see copies as they get made – if they get made that is. You can’t make copies of something that isn’t there, so if scientists see fluorescence above a threshold set for background “noise,” a sample is considered positive for the virus – but if the fluorescence stays below the threshold, in the noise region, the sample is considered negative (although tests usually check for at least 2 targets to be really sure). 

One “slight inconvenience” when it comes to SARS-Cov-2 is that it is a single-stranded RNA virus – it stores and transmits its genetic blueprint (genome) in the form of a single strand of RNA instead of double-stranded DNA like we have. But PCR works by making copies of DNA. So, after scientists extract the viral RNA from patient samples they convert it to DNA form in a process called reverse transcription before doing the copying. Thankfully, this is fairly easy, and it’s the extraction part that is the biggest time (and “needed things”) hold-up. Speaking of which, if you are a scientist with extraction kits to spare check out this page on the RNA society’s website to see how you can help:  

So the basic premise of the test is – doctor collects patient sample (often taken by swabbing the nose and/or throat) and sends it to a lab and then the lab scientists:

  1. extract the RNA
  2. reverse transcribe that RNA into DNA form in preparation for copying
  3. copy it and copy it and copy it… and detect the copies as they’re made

Social distancing

If you want to help out all those doctors and scientists performing the tests, lower how many tests they need to do! In addition to washing your hands (and leaving some things on the store shelves for others…) you can practice what’s referred to as “social distancing” – basically avoiding large gatherings and unesscesqary trips & taking things “virtual” whenever possible (like holding teleconference meetings instead of in-person ones). The main goal of this “mitigation” strategy is to slow the spread of the virus so that our health care system doesn’t get overwhelmed with a whole flood of cases coming all at once. Social distancing is a way to “flatten the curve” (graph of number of cases over time) so that our hospitals don’t run out of equipment like respirators and even beds. 

And slowing the spread is especially important for helping those most vulnerable to getting serious disease from it (serious pneumonia) as opposed to just the mild symptoms most people experience (such as dry cough and fever). Those at highest risk are people who are older, have pre-existing health conditions (lung disease, heart disease, diabetes, etc.), and/or a compromised immune system. I’m sure that every person reading this post has friends and/or family members that meet those criteria, and I hope you’ll think of them when contemplating whether to go to some big event (assuming it hasn’t been cancelled). 

Leave a Reply

Your email address will not be published.