Chinanews client, Beijing, January 17 (Reporter Song Yusheng) On the 15th, 31 provinces added 115 new confirmed cases of new coronary pneumonia, of which 90 cases were reported in Hebei Province, and 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 rounds of full-staff 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 only positive after multiple nucleic acid tests.

  Many netizens wonder: Is the nucleic acid malfunctioning, or the virus is cunning?

Data map: Medical staff collect throat swabs for citizens on the "nucleic acid sampling mobile vehicle".

Photo by Zhai Yujia

Nucleic acid tests have been negative in many cases

  Since the emergence of the new crown pneumonia epidemic, "nucleic acid testing" has become a familiar term.

  Nucleic acid testing is mainly to detect whether there is new coronavirus nucleic acid in nasopharyngeal swabs, throat swabs, sputum and other specimens. A positive test result means that they are infected with the new coronavirus.

From a professional point of view, screening of new coronavirus infections 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, the news that “confirmed cases have repeatedly been negative for nucleic acid” is not uncommon.

  For example, the reporter combed and found that among the 84 newly diagnosed 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, the "confirmed case 51" on the 3rd, 5th, 7th, 9th, 11th, 12th 6 nucleic acid tests were negative; the nucleic acid test was positive on January 13th.

  "Confirmed Case 12" had 5 nucleic acid tests negative on January 3, 4, 6, 9 and 11; however, a throat swab was collected on January 12, and the nucleic acid test was positive on January 13; A confirmed case was diagnosed 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 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 confirmed 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.

Data map: Residents of Gu'an County, Hebei Province are undergoing full nucleic acid testing.

Photo by Men Cong Shuo

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" 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, director of the Dalian Civil Affairs Bureau, also mentioned that “some cases have undergone 11 nucleic acid tests before they are positive. There were also positive cases in 6 rounds."

  So, what affects the results of nucleic acid testing?

  "It is clear that nucleic acid testing is definitely not 100%." ​​Wang Guangfa, chief physician of Peking University First Hospital, said bluntly in an interview with a reporter from Chinanews.com 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 detoxify too much, but may not find out if they detoxify less."

  This week, Gao Weili, director of the Microbiological Laboratory of the Shijiazhuang 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 detoxified.

The high probability is that the amount of detoxification of the patient's respiratory tract each time is very small, so it is not easy to detect.

Data map: Medical staff prepare for sampling in Changjiu Garden Community, Shijiazhuang, Hebei.

Photo by China News Agency reporter Zhai Yujia

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 found to be positive, most likely because different patients have different detoxification times.

  "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 the 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 talked about this phenomenon in an interview before.

  The explanation he gave is: the infected person or the patient starts to detoxify from exposure to infection, professionally called "strong hidden period", while asymptomatic infected person's detoxification professionally called "pre-hidden period", it 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 positive at the end of the pre-hidden period. This phenomenon is completely understandable.

Data map: Medical staff are preparing for sampling in Changjiu Garden Community, Shijiazhuang, Hebei.

Photo by China News Agency reporter Zhai Yujia

  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 the onset of clinical symptoms. 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 excrete a small amount of toxin during the nucleic acid test, the test result may be negative.

Therefore, it is necessary to repeat multiple rounds of detection.

  According to 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.

  The reporter noticed that as of 20:00 on January 14, the second round of nucleic acid testing in Shijiazhuang City was completed; on January 15, Gaocheng District, Shijiazhuang City had carried out the fourth full-time nucleic acid test; in addition, from January 15th, Shijiazhuang postal courier and takeaway employees carry out a full-time nucleic acid test every 72 hours (except for medium and high-risk areas).

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