On January 15th, there were 115 new confirmed cases of local new coronary pneumonia in 31 provinces of China, of which 90 cases were reported in Hebei Province. The number of new local confirmed cases has exceeded 100 for 4 consecutive days.
Up to now, the number of confirmed cases in Hebei Province is still rising, and several national nucleic acid tests have been carried out in some areas of the province.
After combing through the detailed information of confirmed cases officially released by Hebei Province recently, the reporter noticed that there were a large number of cases that were positive after multiple nucleic acid tests.
Many people wonder: is the nucleic acid test not working, or the virus is cunning?
Since the emergence of the new crown pneumonia epidemic, “nucleic acid testing” has become a household word.
Nucleic acid testing is mainly to detect whether there is new coronavirus nucleic acid in nasopharyngeal swabs, throat swabs, sputum and other samples. A positive test result means that the new coronavirus is infected. From a professional point of view, screening for people infected with the new coronavirus through nucleic acid testing is considered to be the most important means and measure to achieve “early detection” and “early diagnosis.”
However, in recent news reports about the epidemic in many places in the Mainland, there have been news that “confirmed cases have repeatedly been negative for nucleic acid.”
For example, the reporter combed and found that out of 84 newly confirmed cases of new coronary pneumonia in Shijiazhuang from 0-24 on January 14th, 56 cases had a negative nucleic acid test and then turned positive.
Among them, “Confirmed Case No. 51” on the 3rd, 5th, 7th, 9th, 11th, and 12th 6 nucleic acid tests were all negative; the nucleic acid test was positive on January 13th.
“Confirmed Case No. 12” had 5 nucleic acid tests negative on January 3, 4, 6, 9 and 11; however, throat swabs were collected on January 12, and the first nucleic acid test was submitted on January 13. Positive; diagnosed as a confirmed case on January 14.
Similarly, at 0-24 o’clock on January 14, two of the six newly confirmed cases in Xingtai also had a negative nucleic acid test.
Among them, “Confirmed Case No. 6” on the 4th, 5th, 7th, and 10th nucleic acid test results were all negative. The nucleic acid test result was positive on the 14th.
Among the 83 newly diagnosed cases of new coronary pneumonia in Shijiazhuang from 0-24 on January 15th, only 14 cases were positive in one nucleic acid test, and the rest were confirmed after multiple nucleic acid tests; on the same day, Xingtai City Among the 7 newly confirmed cases of new coronary pneumonia, only 1 case was positive for a nucleic acid test.
Why can’t it be detected?
In fact, the phenomenon of being positive after multiple nucleic acid tests does not only occur in Hebei. Similar situations have appeared many times before.
A few days ago, “Someone in Shijiazhuang only tested positive for 6 nucleic acid tests” was on the Internet hot search list.
In Liaoning, on January 4, at a press conference on the prevention and control of the epidemic in Dalian, Tang Yi, the director of the Dalian Civil Affairs Bureau, also mentioned, “Some cases have undergone 11 nucleic acid tests before they are positive, and some areas have tested positive. There were also positive cases in 6 rounds.”
So, what affects the results of nucleic acid testing?
“What is more clear now is that nucleic acid testing is definitely not 100%.” Wang Guang, chief physician of Peking University First Hospital, said bluntly that similar situations had occurred in many places, including Wuhan.
As for the factors that affect the test, they include the following: the concentration of the patient’s detoxification, the quality of the test sampling, the quality of the kit, and the laboratory operation.
Wang Guangfa believes that, theoretically, among many factors, the test results are mainly affected by the patient’s detoxification concentration. “Patients can find out if they have a lot of detoxification, but they may not be able to find out if they are less.”
This week, Gao Weili, director of the Institute of Microbiology, Shijiazhuang City Center for Disease Control and Prevention, also talked about this phenomenon in an interview with the media.
He explained that there are many reasons for this phenomenon, the most important being the amount of respiratory secretions discharged. The high probability is that the patient’s amount of detoxification per respiratory tract is very small, so it is not easy to detect.
Nucleic acid testing is still the “gold standard.”
So, what is the reason for the patient’s low detoxification?
Wang Guangfa told reporters that this is related to the progression of the disease. After multiple nucleic acid tests, it was positive, most likely because of the different time of detoxification for different patients.
“The nucleic acid just after the close connection is indeed very likely to be negative.” He said, “The situation we have now is roughly the last two days of the incubation period before positive. And the incubation period of each patient is different, so the virus is detected. The time is different.”
Feng Zijian, deputy director of the China Centers for Disease Control and Prevention, also mentioned this phenomenon in an interview before.
The explanation he gave is: the infection of the infected person or the patient starts to detoxify from exposure to the virus, which is professionally called the “strong hidden period”, while the detoxification of asymptomatic infected persons is professionally called the “pre-hidden period”, which can also be called laboratory testing. Screening window period. During the window period, the test may not be positive for many times, but it will be detected at the end of the pre-hidden period. This phenomenon is completely understandable.
Cao Wei, deputy director of the Department of Infectious Medicine at Peking Union Medical College Hospital, pointed out that current studies have confirmed that the most active time for the new coronavirus to replicate and excrete in the pharynx is before and after clinical symptoms appear. At this time, the pharyngeal nucleic acid test is most likely to be positive. “But this time period is not that wide.”
According to the above statement, if the patient happens to have a small amount of toxins during the nucleic acid test, the test result may be negative. Therefore, it is more necessary to repeat multiple rounds of detection.
In the view of Wang Guiqiang, director of the Department of Infectious Diseases at Peking University First Hospital, these conditions are normal and there is no need to panic.
Previously, many experts have made it clear on different occasions that the positive result of nucleic acid test is still the “gold standard” for the diagnosis of virus infection.
Many areas in Shijiazhuang have undergone multiple rounds of nucleic acid testing. As of 20:00 on January 14, the second round of nucleic acid testing in Shijiazhuang City has been completed; on January 15, the fourth round of nucleic acid testing in Gaocheng District, Shijiazhuang City has been carried out; in addition, starting from January 15th, Shijiazhuang City Postal Express and Takeaway employees carry out nucleic acid tests for all employees every 72 hours (except for medium and high-risk areas).
Read more articles