Recently, citizens raised some questions about nucleic acid testing, and on November 25, Guangzhou organized a special investigation on "nucleic acid results are suspected to be inaccurate." So why do you need to undergo frequent nucleic acid testing? How do "false negative" and

Recently, citizens raised some questions about nucleic acid testing . On November 25, Guangzhou organized a special investigation on "nucleic acid results are suspected to be inaccurate." So why do you need to undergo frequent nucleic acid testing? How do "false negative" and " false positive " occur? How to avoid deviations in nucleic acid testing? To this end, a reporter from Nandu interviewed Zhao Wei, director and professor of the Biosafety Research Center of the School of Public Health of Southern Medical University.

Haizhu A community nucleic acid test.

Question: Why do we need to conduct nucleic acid tests frequently?

Zhao Wei: Nucleic acid testing is a mature and internationally universal laboratory diagnosis method. It is an effective means to detect the new coronavirus in the human body. It is the current international standard for determining positive infections. It is also known as the "gold standard" for judging positive .

Omickron mutation has a shorter incubation period, stronger infectiousness, faster transmission speed, and a higher risk of occult transmission. If you want to pass a nucleic acid test, you can discover all infected people or sources of infection. It is difficult to win with one move, because false negative results may occur. Therefore, in the face of the "unusual" Omickron , rapid, expanded and high-frequency large-scale nucleic acid testing is an important strategy to outperform the spread of the virus.

Question: What errors may occur in nucleic acid testing of ?

Zhao Wei: In summary, there are three situations: technical deviation, improper operation and illegal behavior.

Technical deviation: There is an error in a single result of large sample detection objectively, but this is a very rare case;

operation error: the detection volume is large, and the operation method and environmental impact will lead to misjudgment of results;

violations: Some individuals and institutions violate regulations and illegal behaviors, which are malicious criminal behaviors, and this situation has also occurred in some places in China.

Question: How do "false negative" and "false positive" occur?

Zhao Wei: (1) False negative: New coronavirus patients have a "window period" and have a small amount of detoxification. When the infected person receives sampling, they cannot detect or the test result cannot meet the positive judgment criteria. It can only be detected after a few days of sampling and testing, becoming the so-called "false negative", which belongs to the false negative of the entire detection system; also has a situation where although there are viral nucleic acids in the sample, it cannot be detected due to the sensitivity of the detection method, which belongs to the false negative of the detection method.

(2) False positive: mainly because the reagent is contaminated during sample collection and on-machine testing, the test result is positive, and it is determined to be negative after resampling and review. Or because of the problem of the detection method, it reacted with the non-specific nucleic acid in the sample, which is a false positive in the detection method.

nucleic acid testing site in Yueran Plaza, Beijiao, Shunde, medical staff took a pharyngeal swab for a delivery boy.

Question: Some citizens encounter situations where the antigen test is negative and the nucleic acid test result is positive. Why is this?

Zhao Wei: Antigen detection is less specific and sensitive than nucleic acid detection, and false positive or false negative results may occur. If the antigen detection operation occurs inappropriately, such as excessive detection volume, failure to use the kit in time after opening, etc., it may cause false positive results. At the same time, since there is no amplification step in antigen detection, it is difficult to detect when the virus is small. Therefore, when the infected person has a low viral load in the early stage of the virus infection, it is very likely that misjudgment will occur and no positive test will be detected.

The "Application Plan for Antigen Testing of New Coronavirus (Trial)" issued by the State Council in March 2022 clearly stipulates that nucleic acid testing is the basis for the diagnosis of new coronavirus infection. Therefore, antigen detection can be used as a supplementary means of nucleic acid detection and helps early detection, but cannot be used as the "gold standard" to determine whether the detection object is infected with the virus.

During the process of nucleic acid testing and confirmation, if the nucleic acid test is positive, no matter whether the antigen test result is negative or positive, the corresponding measures will be taken in accordance with the new coronavirus infected person or confirmed patient of new coronavirus pneumonia; if the nucleic acid test is negative but the antigen test is positive, it will be deemed that the new coronavirus infected person will take centralized isolation and other measures, closely observe, and conduct subsequent nucleic acid tests continuously.

Question: How to avoid deviations in nucleic acid detection by ?

Zhao Wei: (1) Avoid "false negative": Through multiple rounds of nucleic acid screening, accurately screen out infected people; further improves the sensitivity of detection technology.

(2) Avoid "false positives": Strengthen laboratory quality control, municipal quality control experts "daily inspection", district and county experts "on-site guidance", and conduct quality supervision throughout the process. If the quality evaluation results fail, their testing business will be suspended immediately. further improves the specificity of detection technology.

(3) Severely punish violations of regulations and laws: zero tolerance, and severely crack down on them in accordance with the law. For the detection errors reported by citizens, the investigation procedures will be initiated immediately in accordance with the law. Once discovered, severe punishment will be made.

Interview and writing: Nandu reporter Yang Liyun