What does "intermittent detoxification" mean by the new crown? Is multiple nucleic acid tests necessary?

True points:

The "intermittent detoxification" mentioned in the news report is a response to the dynamic infection process of the virus, such as the virus load is getting lower and lower during the process of patient recovery, and the nucleic acid test will sometimes be detectable and sometimes undetectable. In order to more accurately grasp the situation of infected individuals, a more scientific approach is to sample multiple rounds of nucleic acid testing.

Verified by: Han Yue 丨 Postdoctoral Fellow in Virology, University of Cambridge

The Spring Festival is approaching, and the epidemic in Xi'an has touched the hearts of countless people. In recent days, the topic of "intermittent detoxification in a small number of people infected with new crown" has attracted a lot of attention. What's going on here?

1. What is virus detoxification?

First of all, virus detoxification, to explain this phenomenon, but also from the replication cycle of the virus and the ability of virus to spread.

The structure of the virus is actually very simple, usually containing only the protein shell and genetic material nucleic acid (DNA or RNA), and the replication of nucleic acid depends on the host cell. So in order to survive, the virus must infect another organism. Once in an organism, the virus invades a cell that provides the conditions needed to replicate more of the virus. Newly produced virus particles can continue to infect other cells, and the number of viruses in individuals increases exponentially with each round of replication.

In the process of continuous replication of the virus, the longer it takes an individual's immune system to recognize and control this process, the greater the number of viral particles produced and the more intense the battle between the virus and the immune system. Infected individuals end up embodying the battle in the form of symptoms of the disease – fever, fatigue, congestion, vomiting, diarrhea, etc.

Similarly, for covid-19, the main site of early infection of the virus is the respiratory system, especially the cells inside the nose and throat, and then the virus may enter other parts of the body, where they can infect more cell types and cause additional symptoms or complications. But these newly formed viral particles may also have a different fate, they can stay in the nasal cavity and oral secretions of the infected person (a process called virus shedding, the virus shedding), when the infected individual speaks, exhales, eats and performs other normal daily activities, the virus particles are released, thus infecting others.

Under normal circumstances, the virus does not stay in the human body for more than a few weeks, but gradually disappears with the virus clearance process in the infected person's body. As we gained a deeper understanding of the mechanisms by which the virus cleared, the researchers found that the virus persisted in certain populations for longer. There is growing evidence that the virus begins before a patient develops symptoms, peaks when symptoms appear or shortly after they appear, and persists even after symptoms disappear.

To sum up, the detoxification period of the new crown virus is actually the time when the virus continues to replicate and reproduce after infecting the human body, and the detoxification may begin before the symptoms appear, and the detoxification may continue after the symptoms disappear.

2. What does "intermittent detoxification" mean? Is multiple rounds of nucleic acid testing necessary?

It has been reported that multiple rounds of nucleic acid screening are carried out because "a small number of new crown infected people have intermittent detoxification phenomenon", "the new crown virus has a certain incubation period, a small number of infected people have intermittent detoxification phenomenon, and sampling is only a time point, if the sampling is not detoxified or the virus concentration is not enough at that time, below the detection limit, it may not be detected, especially for asymptomatic infected people, the early detoxification level is not high, and the virus concentration in the body is very low."

Strictly speaking, there is no concept of "intermittent detoxification" in medicine, and the process of viral detoxification is not "intermittent". The "intermittent detoxification" mentioned in the report is actually a reaction to the dynamic infection process of the virus.

At present, the new crown virus infection is confirmed by nucleic acid detection (PCR), which is actually an indirect detection of virus exfoliation in nasal and oral secretions. In the early stage of infection, the virus is still in the early stage of replication, the virus content in the nasal cavity and oral secretions is extremely low, may be lower than the detection value, can not be detected by nucleic acid detection; if the operation of the sampling process is not standardized, may not be able to collect the correct sample, can not detect the presence of the virus; it is also possible that in the process of infection, because of the role of the immune system, the content of the virus is suppressed at a very low level in a certain period of time, and the virus cannot be detected, and the nucleic acid is negative. However, it is not excluded that the virus will continue to proliferate in large quantities in the later stage and may be tested positive again. In addition, in the process of patient recovery, the virus will gradually be excreted, and the viral load will become lower and lower, so nucleic acid testing will sometimes be detectable and sometimes cannot be detected.

This also means that the nucleic acid detection results at a single time node do not reflect the entire process of virus infection, in order to more accurately grasp the situation of virus-infected individuals, a more scientific approach is to sample multiple rounds of nucleic acid testing, rather than only at a time point after testing to determine whether an individual is infected with the new crown virus.

This article was edited by Ambergchen

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