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There are 7 known coronaviruses that can infect people. Three of them are more dangerous, MERS, SARS virus, and this time SARS2 virus.

The virus looks like this. The outer layer of the sphere is the envelope and proteins, and inside is RNA, the full name of RNA, the nucleic acid test, which targets it.

The smallest structure that makes up RNA is called ribonucleotide, and there are four types: A, U, C, and G. The smallest structure that makes up RNA is called ribonucleotide. The smallest structures that make up RNA are called ribonucleotides, and there are 4 types of A, U, C, and G.

The SARS2 virus, which has been sequenced, consists of about 30,000 letters. Sequencing technology has really advanced rapidly over the years, as the SARS virus in 2002 took 5 months to sequence, and this one is said to have taken only 10 days.

If you are interested, you can go to the NCBI website to get the raw data, and everything is very public.

But sequencing is expensive and inefficient, and RNA sequencing is not the nucleic acid test in this case, it is the prerequisite for nucleic acid testing to work. Nucleic acid testing, using real-time polymerase chain reaction, is RT-PCR technology, which cannot measure every letter of the virus, but can determine whether it is present.

To complete the nucleic acid test, three main parties need to work closely together: the physician sampling, the kit development and the laboratory testing.

Firstly the doctor collects the patient's sample, which is a demonstration of collecting a nasopharyngeal swab, which is close and may cause infection. Secondly nucleic acid testing is a very complex biochemical reaction to identify the SARS2 virus, which requires targeted development of kits and completion of production. Finally both patient samples and kits are sent to the laboratory, which comes out with the site, instruments and laboratory staff to complete the test here.

What happens after that, I'll try to present briefly.

Let's assume that this is a sample that does contain the SARS2 virus. The first step is to extract the viral RNA, or nucleic acid, from the sample. However, since RNA is structurally unstable, it needs to be converted into DNA first, using the reverse transcriptase and DNA feedstock provided in the kit.

After reverse transcription is completed, the two strands are separated and the viral message is passed on, after which all reactions are related to this single strand of DNA.

The core of the entire assay is to allow the DNA to continuously replicate itself and accumulate fluorescent signals. To achieve this, let's focus on the kit.

The kit contains primers, DNA feedstock and various reaction enzymes that help the DNA to replicate continuously. The probe in the kit, which has a fluorescent structure on it, is responsible for releasing the fluorescent signal.

First, the probe binds to the DNA, where the fluorescent structure is inhibited from emitting light. Then the DNA starts to replicate itself by the action of polymerase, and the fluorescent structure comes off and starts to emit light.

At the end of the reaction, we get a double-stranded dna and a luminescent body. But this amount is too small for the machine to detect the fluorescence signal. So several more cycles are needed, usually set to 40.

Ideally, if the SARS2 virus is present in the patient sample, there is an S-shaped curve between the number of cycles and the amount of fluorescence, i.e. a positive nucleic acid test. Without or with a small amount of SARS2 virus, there is no similar curve, i.e., a negative nucleic acid test.

So why is there a false negative nucleic acid test?

This is also quite complicated. Let's go back to the three parties that affect nucleic acid testing.

Sampling comes with a lot of uncertainty. Samples from different sites have different success rates, and deep cough sputum from the lower respiratory tract works better compared to a nasopharyngeal swab. The duration of the patient's illness also affects, exactly which days of onset the test has a high success rate, which requires more clinical data for further analysis.

In addition to this, the sampling technique of the person taking the sample, whether the sample is contaminated, and whether it is sent to the laboratory in a timely manner can all affect the success rate.

There may also be problems with the reagent kit. The design level is on one hand, and on the other hand, if the virus is mutated, it may not be identified. Good design but poor production process will not work either. Therefore, more data feedback is needed for optimization.

Finally, the laboratory side, the need for manual operation of the steps are very much, the experimental staff's operating techniques will also affect the test results.

In short, the current nucleic acid test, a large number of steps, and requires close cooperation between multiple parties to complete, some of the problems have not yet been clarified.

In addition, the virus is highly contagious and requires many additional steps for disinfection, wearing various protective equipment, mobility problems and physical discomfort, which makes the test even less efficient.

Since February 6, there are currently 97 laboratories in Hubei Province approved, and the maximum daily testing volume at saturation is only 10,000, while the positive rate of nasopharyngeal swabs is only 30%-50%.

So if we are dealing with a less infectious virus with fewer cases, such a nucleic acid test may be an option.

But in the face of an outbreak, nucleic acid testing is not suitable as a rapid screening tool for patients because of its many steps and time consuming nature.

Compared to MERS and SARS, SARS2 has a lower mortality rate, but is more contagious and infects a larger number of people, so how to do rapid screening and what testing technology to use is critical.

Recently there have been some new testing techniques that have started to be tested, but hopefully there will be good news soon and they will be available as soon as possible.

Interfacing with laboratories is part of my job and I know how hard the testers work and I would like to thank them for their dedication.

Any technology has its limitations, which is something we need to be alert to and keep in mind when applying it to our lives, and of course the process is complex and comes at a cost.

The same is true for the development of vaccines and drugs. In the face of unknown challenges, we hope that new breakthroughs will be made in biogenetic technology.