How Testing For Covid-19 Works

How the process runs, why we’re not testing everyone who feels ill, and something you can do online immediately and easily to help the fight against the virus.

Testing for Covid-19 isn’t like a pregnancy test. You don’t just pee on a stick, wait a few minutes and get a result. Allow me to explain.

Step 1: Take a sample
To test for Covid-19 you first need the right samples, and these will differ depending on the person and the symptoms they present with. So, the first important thing is whether the right sample is taken by a competent person. To scale up our testing we would have to put resources in to making sure we had enough people trained up to take the swabs. We can do this, but it will take resources away from somewhere else.

For most people, a simple swab can be taken from the mouth and throat, or the back of the nose (check out the video here). For others, we might use sputum, which is the gunk coughed up from the lungs by some patients. For some, the sample might be from a procedure called a bronchoalveolar lavage. To get this sample, someone puts a tube down your mouth or nose into your lungs, squirts some fluid into your lungs, and then collects the fluid back again. Some people have had negative throat and nose swabs but positive bronchoalveolar lavages.

Oh, and guess what. The long cotton-bud thing they use to take the swabs comes from overseas. Again, sourcing them at some point may become an issue.

Laboratory technicians testing samples of virus at a laboratory in Hengyang in China's central Henan province

Step 2: Send samples to the lab
We have several labs around each country all set up to test for the Covid-19 coronavirus, and these labs are also currently doing diagnostic tests for other diseases that aren’t likely to just disappear.

Again, to get greater capacity, people will be being trained up to process and test the samples. If we needed to do more, we could use the labs and scientists in our country’s universities and Research Institutes. They would need proper training though to make sure they were carrying the tests out to the appropriate standard.

Step 3: Extracting the virus
To understand the next step of the test, it helps to know a little more about the virus responsible. Think of it like a bar of chocolate - a filling encased in a layer of chocolate, served up in a wrapper. The filling is the virus’s genetic material, the chocolate its proteins, and the wrapping a layer of lipids. The Covid-19 coronavirus’ genetic material is RNA.

Once you have a sample, next you have to extract the virus’s RNA from all the other stuff – the human cells, the bacterial cells, and any other junk. This is done in a special type of lab using a commercial kit.

Around the world, scientists are trying to develop ways to bypass this step so the test can be run straight from the patient samples.

Step 4: Detecting the Covid-19 coronavirus
After extraction then it’s time to see whether the Covid-19 coronavirus is present in the sample. The test is what is known as a nucleic acid amplification test (NAAT) and is based on detecting unique sequences in the virus’s RNA by a method called reverse-transcription polymerase chain reaction (rRT-PCR). Because the Chinese released the genetic sequence of the virus so quickly, that allowed tests to be developed and the methods released to the world so any country could do the test if it needed to. This is where the US screwed up. They decided to develop their own test instead. And then that ended up not working properly, which lost them valuable time.

This part of the test also uses special reagents and again these are commercially available and imported from overseas. The kit, and a piece of equipment that switches temperatures really fast, turns any RNA present into DNA and then if any of that RNA belonged to the Covid-19 coronavirus it makes loads and loads of copies of it which can be detected. This is what gives a positive test. If none of the RNA belonged to the virus then there shouldn’t be a detectable signal.

The limiting factors at this stage are the availability of the reagents and the amount of virus present in the sample. Too little virus and the test won’t be able to pick it up.
 
As some countries are heading into flu season, they will need to make sure we have enough reagents to be able to do those tests too.

What about reports of ‘hidden’ cases?
A study just published has reported that in the early stages of the Covid-19 outbreak in China, as many as  five to 10 people infectious people were shedding the virus for every one case that was diagnosed. One thing to remember about this study is that it is based on a limited number of cases from early in the outbreak.

Analysis of over 50,000 cases led the WHO and Chinese health officials to conclude that around one out of every six people who gets Covid-19 becomes seriously ill and develops difficulty breathing.

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