Recently, the epidemic situation in many parts of the country has been sporadic, and the epidemic prevention and control situation in Shanghai is still grim, and many places have organized large-scale and high-frequency nucleic acid testing.
Every time the result is negative, why do you need to continue testing? Is it necessary to continue to do nucleic acid testing on a high frequency now?
▲Data chart Wu Junjie photo
Race with nucleic acid testing and viruses
For hundreds of years, the basic principles of controlling infectious diseases have not changed: control the source of infection, cut off transmission routes, and protect susceptible people.
Why do nucleic acids continuously?
Zhao Jing, an expert at the Shanghai Working Group of the Comprehensive Group of the Joint Prevention and Control Mechanism of the State Council, said in a recent interview with the media that the purpose of carrying out large-scale or full nucleic acid screening is to quickly find out the positive infected people from the population, and then play a role in controlling the source of infection.
Zhao Jing stressed that we have been stressing the need to race against the virus and use nucleic acid testing to race against the virus. If there is an epidemic in any place, when we go to deal with it, we see this place as a battle. Nucleic acid testing is to fight the charge, the length of this battle, the size of the scale, mainly depends on the charge to fight well. Only by finding out the source of infection through nucleic acid detection can the follow-up can be traced back to the source, community sealing, isolation and control, and so on.
Frequent repetition of multiple inspections is necessary
Gao Chunfang, director of the Laboratory And Experimental Center of Yueyang Hospital affiliated to Shanghai University of Traditional Chinese Medicine, said at a press conference on the prevention and control of the new crown pneumonia epidemic in Shanghai on April 17 that it is necessary to repeat the test multiple times at a high frequency.
Nucleic acid detection is a highly accurate and effective method for detecting pathogens in infectious diseases. Clinical pathogen detection has four categories: classical morphological staining, traditional biochemical reactions, immune responses (detection of antigen antibodies) and pathogen nucleic acid detection. Nucleic acid testing is a very effective and very important means in the current epidemic prevention and control.
For why high-frequency repeated detection, Gao Chunfang introduced the following three main reasons:
First, from the perspective of the occurrence and development of clinical diseases, any pathogen infection has a certain incubation period, and the new crown is no exception, and there are certain individual differences in the length of the incubation period.
Second, from the perspective of detection technology, there is the concept of detection window period. After the virus infection, there is a growth and replication process in the body, the initial viral load of infection is too low, lower than the lower limit of detection, positive can not be found, this time period is the detection window period. The above infection incubation period + detection window period makes it not necessarily possible to detect a positive result at the beginning of infection, and repeated multiple tests can increase the probability of positive detection and timely detection of positive.
Third, since the sampling of respiratory pathogens mainly uses several forms of throat swab, nasal swab, nasal + throat swab, there are inevitably certain sampling differences in the sampling process. This difference includes the location of the sampling, the depth of the sample, and the amount of secretion collected. Therefore, repeated multiple sampling detection can compensate for the false negative effects that may be caused by sampling errors.
Infected people with a low viral load
Initial nucleic acid may be negative
For why it is necessary to carry out nucleic acid testing for many consecutive days in the sealing and control area, Hu Xiaobo, director of the Shanghai Clinical Laboratory Center, also stressed in an interview recently that when the community completes a round of nucleic acid screening, usually infected people with a high viral load can be screened out, but there are also some infected people with a low viral load who will show negative nucleic acid results in the initial stage, and only when more and more virus replication in their bodies can they be found through testing. If the latter is not detected in time, it can become a potential spreader in the community.
Therefore, it is necessary to dynamically find positive infected people as soon as possible through multiple rounds of nucleic acid screening in a row, and achieve dynamic zero social clearance as soon as possible.
Achieve zero at the social level
Nucleic acid testing for all employees
It is the most effective strategic measure
Wu Zunyou, chief expert of epidemiology at the Chinese Center for Disease Control and Prevention, said in a document on April 7 that when the epidemic spreads widely at the community level, nucleic acid testing is the most effective strategic measure to achieve zero at the social level. Nucleic acid testing for the purpose of zeroing out, one should be fast, and the other should be complete.
The average incubation period of the Omiljung strain is 3 days, and confirmed cases generally begin to excrete the virus 1-2 days before the first onset of symptoms. That is to say, if a person has effective contact with a person infected with the new crown (that is, is infected), the nucleic acid test is performed on the same day or even the next day, and it is basically negative. The third day of nucleic acid testing is meaningful.
Wu Zunyou explained that when the first round of full screening is completed, those infected and have been detoxified outside the body can be screened out. But those infected who are infected with the virus but have not yet been detoxified outside the body will show nucleic acid negative in the first round of screening. These infected people who have not yet been detoxified will continue to stay in the community, and if they are not detected in time, they will soon develop into infected people who are detoxified outside the body and are contagious, and will continue to spread the virus in the community.
Therefore, the second round of screening must be carried out immediately before it can transmit the virus to others, so that it can be screened out and the transmission can be cut off. Because nucleic acid testing is super sensitive, as long as there is a virus in the throat area, it can generally test positive. If an infected person tests negative and cannot collect the virus by sampling with a cotton swab, the risk of transmitting the virus to others within 24 hours by breathing or speaking is almost negligible.
Wu Zunyou stressed that the screening of all employees must be fast, and the second round, the third round, and the fourth round of screening must be carried out one after another, round after round, and zero at the social level can be achieved quickly.
This article is reproduced from the WeChat public account "China Women's Daily", source: Guoshi Express, CCTV News, Xinhua News Agency, Wu Zunyou Weibo