On March 26, Changsha City found 2 confirmed cases of new coronary pneumonia in regional nucleic acid screening. Among them, case 1 Tang Moumou belonged to a close contact of Zhang Mou, who was confirmed on March 14, but he had all negative nucleic acids during the isolation period from March 14 to 21. He returned to the place of residence for health monitoring on the 21st, and the nucleic acid was initially screened on the 26th. positive. (Previously notified: Changsha City found 2 confirmed cases of new coronary pneumonia in the regional nucleic acid screening) Faced with the new coronavirus in the incubation period, how many times does nucleic acid need to be insured? Zhan Zhifei, chief technician of the micro-examination section of the Hunan Provincial Center for Disease Control and Prevention, gave a detailed interpretation to the media. How is a nucleic acid test determined to be positive? It took multiple nucleic acid tests to show positive results. Could it be that this technology that can make the new coronavirus “reveal” fails? of course not! “The stability of nucleic acid testing itself is good. The so-called ‘undetectable’ or ‘false negative’ situation occurs mainly because any testing method has a sensitivity problem.” Zhan Zhifei said. Like the SARS coronavirus, the new coronavirus is composed of RNA (ribonucleic acid) and protein. It invades cells through receptors on the surface of specific cells to cause infection, and uses the infected cells to replicate and multiply. Therefore, medical personnel can confirm whether the body is infected by collecting cell samples from specific parts of the person and testing whether they contain viral nucleic acid. Taking the currently commonly used fluorescence quantitative PCR (polymerase chain reaction) technology as an example, suppose someone is a carrier of the new coronavirus and needs to undergo nucleic acid testing. It is fully inactivated so that its original structure is destroyed and the nucleic acid is exposed, and then reagents are used to check whether it can be highly matched with certain key parts of RNA (ribonucleic acid). Each time the match is successful, a corresponding fluorescent signal will be generated, indicating that the “gene ID card” has been recognized, and the PCR detector will record the fluorescent signal value in real time. After repeated inspections, the fluorescence intensity is getting higher and higher, and an upward curve will appear on the detection software, indicating that the test is positive, proving that the sample contains the RNA of the new coronavirus. Why are multiple nucleic acid tests positive? Tang Moumou’s nucleic acid has been negative several times because the tested person has been in the incubation period before. Zhan Zhifei explained that people are not necessarily infected after contact with infected people, but if they can test positive for nucleic acid after a certain period of contact, they are infected. No positive nucleic acid detection does not necessarily mean that you are not infected, which is related to various reasons such as sampling and virus proliferation. Zhan Zhifei said that the nucleic acid test of the new coronavirus is one of the necessary conditions for a positive diagnosis. Nucleic acid detection is a multi-link workflow, including sampling, specimen transfer, specimen receipt, nucleic acid extraction, nucleic acid amplification, etc. Improper operation of any link may lead to “false negatives”. “The most important thing is the amount of detoxification of respiratory secretions.” Zhan Zhifei said that some tested subjects had extremely low detoxification during the incubation period, and nucleic acid testing at this time could easily lead to “false negatives”. Current research has confirmed that the most active time of new coronavirus replication and excretion in the pharynx is before and after the onset of clinical symptoms. At this time, a throat swab is most likely to be positive for nucleic acid testing. However, there may be individual differences in the window period from the time of infection to the time when a positive test can be detected, and it is not excluded that some cases have a longer window period. After being vaccinated for a period of time, even if you are infected with the new coronavirus, the antibodies produced by the human body will neutralize and eliminate the new coronavirus, resulting in a lower detection rate of the new coronavirus, and multiple nucleic acid tests are required to ensure insurance. How many times does the nucleic acid test need to be “insured”? The Omicron variant that caused the recent epidemic in many places has the characteristics of strong infectivity, fast transmission, relatively mild symptoms, strong concealment, and difficulty in detection. Early screening can stop the chain of virus transmission and avoid infecting more people. According to Zhan Zhifei’s analysis, cases that are positive after multiple nucleic acid tests generally appear in high-risk areas or key groups. For key groups, multiple nucleic acid tests may be required when the risk is not eliminated. For example, for close contacts, the amount of detoxification of respiratory secretions is not large at the beginning, and the throat swab may not be detected, but it does not mean that there is no virus in the body. Due to individual differences, tolerance and previous disease conditions between different people will have a certain impact on sampling. Therefore, how many times the nucleic acid detection of the new coronavirus needs to be done depends on many comprehensive influencing factors. “The fact that multiple nucleic acid tests are positive does not affect the fact that nucleic acid testing is the gold standard for the diagnosis of the new coronavirus. That’s why it is more necessary to repeat multiple rounds of nucleic acid tests.” Zhan Zhifei said that multiple nucleic acid tests appeared It is normal for the test to be positive, and residents do not need to worry at all, as long as they carry out nucleic acid testing according to local epidemic prevention and control requirements.
（Sanxiang Metropolis Daily）