A large number of cases tested positive only after multiple nucleic acid tests. Has the virus become more cunning?

Some people in Shijiazhuang took 6 nucleic acid tests before they showed positive, and some people in Dalian took 11 nucleic acid tests before they showed positive...

On the 15th, 115 new local confirmed cases of COVID-19 were reported in 31 provinces, of which 90 were reported in Hebei Province. The number of new local confirmed cases has exceeded 100 for four consecutive days. So far, the number of confirmed cases in Hebei Province is still rising, and some areas of the province have carried out multiple rounds of nucleic acid testing for all residents. After sorting out the detailed information of confirmed cases announced by the Hebei authorities recently, the reporter noticed that there are a large number of cases that tested positive after multiple nucleic acid tests. Many netizens are wondering: Is the nucleic acid not working, or is the virus cunning?
Data map: Medical staff collect throat swabs for citizens on the "nucleic acid sampling mobile vehicle". Photo by Zhai Yujia

Nucleic acid tests of many cases were negative. Since the outbreak of the COVID-19 epidemic, "nucleic acid test" has become a household word. Nucleic acid testing mainly detects whether there is nucleic acid of the new coronavirus in specimens such as nasopharyngeal swabs, throat swabs, and sputum. A positive test result means infection with the new coronavirus. From a professional perspective, screening for 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, recently, news reports on the epidemic in many places have often reported that "confirmed cases have tested negative for nucleic acid many times."

For example, the reporter found that from 0:00 to 24:00 on January 14, 56 of the 84 new confirmed cases of new coronary pneumonia in Shijiazhuang had negative nucleic acid tests, but then turned positive. Among them, "confirmed case 51" had negative nucleic acid tests on the 3rd, 5th, 7th, 9th, 11th, and 12th; the nucleic acid test was positive on January 13. "Confirmed case 12" had negative nucleic acid tests on January 3, 4, 6, 9, and 11; but he collected a throat swab on January 12, and the nucleic acid test was positive on January 13; he was diagnosed as a confirmed case on January 14. Similarly, from 0:00 to 24:00 on January 14, 2 of the 6 new confirmed cases in Xingtai had negative nucleic acid tests. Among them, "confirmed case 6" had negative nucleic acid tests on the 4th, 5th, 7th, and 10th. The nucleic acid test result was positive on the 14th. Among the 83 new confirmed cases of COVID-19 in Shijiazhuang from 0:00 to 24:00 on January 15, only 14 cases tested positive in a single nucleic acid test, and the rest were confirmed after multiple nucleic acid tests; on the same day, among the 7 new confirmed cases of COVID-19 in Xingtai, only 1 case tested positive in a single nucleic acid test.
Data map: Residents of Gu'an County, Hebei Province are undergoing nucleic acid testing. Photo by Men Congshuo

Why can't it be detected? In fact, the phenomenon of multiple nucleic acid tests before testing positive is not unique to Hebei. Similar situations have occurred many times before. A few days ago, "Someone in Shijiazhuang tested positive for nucleic acid six times" was on the Internet hot search list. In Liaoning, on January 4, at the Dalian epidemic prevention and control press conference, Tang Yi, director of the Dalian Civil Affairs Bureau, also mentioned that "some cases were tested positive for nucleic acid after 11 times, and some areas had positive cases after 6 rounds of testing." So, what affects the results of nucleic acid testing? "What is clear now is that nucleic acid testing is definitely not 100%."

Wang Guangfa, chief physician of Peking University First Hospital, said in an interview with China News Service that similar situations have occurred in many places, including Wuhan. As for the factors affecting the detection, they include the following: the concentration of patient detoxification, the quality of test sampling, the quality of the test kit, and laboratory operation. Wang Guangfa believes that theoretically, among many factors, the test results are mainly affected by the patient's detoxification concentration. "If the patient detoxifies more, it can be detected, and if it detoxifies less, it may not be detected." This week, Gao Weili, director of the Microbiology Laboratory of 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 of which is the amount of detoxification of respiratory secretions. There is a high probability that the amount of respiratory detoxification of the patient 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 Zhai Yujia, a reporter from China News Service

Nucleic acid testing is still the "gold standard" So, what causes the patient to excrete less toxins? Wang Guangfa told reporters that this is related to the progression of the disease. It took multiple nucleic acid tests to test positive, most likely because different patients have different excretion times. "It is indeed very likely that the nucleic acid test will be negative just after close contact." He said, "The situation we have now is generally that the positive test only appears in the last two days of the incubation period. The incubation period of each patient is different, so the time to detect the virus is different."

Feng Zijian, deputy director of the Chinese Center for Disease Control and Prevention, also talked about this phenomenon in an interview. His explanation is that the period from exposure to the virus to the virus excretion of infected people or patients is professionally called the "strong latent period", while the excretion of asymptomatic infected people is professionally called the "pre-latent period", which can also be called the window period for laboratory testing and screening. During the window period, many tests may not detect positive results, but at the end of the pre-latent period, positive results will be detected. This phenomenon is completely understandable.
Data map: Medical staff are preparing for sampling in Changjiu Garden Community, Shijiazhuang, Hebei. Photo by Zhai Yujia, a reporter from China News Service

Cao Wei, deputy director of the Department of Infectious Diseases at Peking Union Medical College Hospital, pointed out that current research has confirmed that the most active time for the new coronavirus to replicate and be excreted from the pharynx is before and after the onset of clinical symptoms, when the possibility of a positive nucleic acid test in the pharynx is the highest. "But this time period is not that wide." According to the above statement, if the patient happens to excrete less toxins during the nucleic acid test, the test result may be negative. Therefore, repeated rounds of testing are even more necessary. In the view of Wang Guiqiang, director of the Department of Infectious Diseases at Peking University First Hospital, these situations are normal and there is no need to panic. Previously, many experts have made it clear on different occasions that a positive result of a nucleic acid test is still the "gold standard" for diagnosing viral infections.

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 of Shijiazhuang City had carried out the fourth full-staff nucleic acid test; in addition, from January 15, Shijiazhuang City’s postal express and takeaway practitioners will undergo full-staff nucleic acid testing every 72 hours (except for medium and high-risk areas).

Source: China News Network