In response to the rapid and insidious spread of Omicron nucleic acid testing has become the main technical means of virus surveillance nucleic acid certificates are also increasingly being verified in travel, entry to premises, etc. What is the validity length of nucleic acid certificates for 24 hours, 48 hours, 72 hours? Some infected people have repeatedly tested negative for nucleic acid before showing positive, nucleic acid mixed test is accurate or not? For the nucleic acid test in the public concern, the State Council joint prevention and control mechanism held a press conference, authoritative experts to answer one by one.
What is the effective length of nucleic acid proof?
During the outbreak, there are different regulations for the valid length of nucleic acid test certificates in various regions and time periods, ranging from within 24 hours, 48 hours to within 72 hours, how are these lengths determined? Li Ang, deputy director of the Beijing Municipal Health and Wellness Commission, said, "Considering that the average incubation period of the new coronavirus Omicron variant is around 3 days, nucleic acid testing within 72 hours can detect potential infections." The length of time was adjusted after risk assessment on the one hand, and to reduce the frequency of nucleic acid testing for residents and reduce the impact on normal life on the other. The development of the nucleic acid testing strategy needs to delineate the scope and frequency of nucleic acid testing according to the needs of epidemic prevention and control, and the tested persons will carry out nucleic acid testing in order from the highest to the lowest risk level," said He Qinghua, first-level inspector of the National Health and Health Commission's CDC Bureau.
"The specific frequency delineation stipulates that the first nucleic acid screening is completed within 24 hours in the sealed control area, 48 hours in the control area, and 48 hours of negative nucleic acid testing proof is required for those who really need to travel in the low-risk areas and preparedness areas where the epidemic occurs. Each region can be adjusted according to the needs of the epidemic prevention and control.
Can a sample from more than a dozen people be tested together and detected as positive?
Li Jinming, deputy director of the National Health and Wellness Commission's Clinical Laboratory Center, introduced: nucleic acid testing is a mature, internationally accepted laboratory diagnostic method, and its specificity can reach 100 percent detection in terms of methodology, becoming the "gold standard" for diagnosis. Li Jinming explained: "the current mixed collection, is five, ten or twenty samples swab in a sampling tube for testing, this practice has been theoretically validated, laboratory validation, field validation, proved that its mixed collection detection rate and single sample no significant difference, is accurate and reliable." What happened to some infected individuals who tested negative for nucleic acid multiple times before showing positive? The vast majority of people who have had multiple negative nucleic acid tests in a row end up with a positive test, but it has happened, and it should be one of these three cases: in the first case, the person was not infected at the beginning and was infected at a later point in time, when the test was positive after infection. Also, when the person is in the incubation period, our test does not detect it, and after the onset of the disease, the test is positive. The third aspect, as mentioned earlier, is that although the virus is present at the beginning and the load does not reach the lower limit of detection, it is also undetectable at this time, but once the load is high, it is detected as positive. Does a positive environmental sample mean there is a live virus? A positive nucleic acid test in an environmental sample does not necessarily mean that there is a live virus in the environmental sample. If the presence of a live virus is identified, cellular virus isolation or virus isolation from sensitive mice must be done to determine whether there is a live virus. Because both dead viruses and live viruses in environmental samples, or we are now playing inactivated new crown vaccine, it contains nucleic acid, nucleic acid test can be detected positive, so the detection of positive nucleic acid does not mean that it has a live virus, to comprehensive research and judgment. Is the sampling swab for nucleic acid testing a cotton swab? Is it harmful to humans? The sampling swab looks like a cotton swab, but it is not a cotton swab, its material is polyester or nylon fiber, it is more similar to our daily life toothbrush, toothbrush bristles are also nylon, but the sampling swab in the process of doing, is millions of tiny fibers vertically and evenly covered in the end of the swab handle above.
At the time of sampling, just like a toothbrush, but it is brushing the posterior pharyngeal wall of our mouth to take cells, and then put the sampling swab into the sampling tube, because it uses nylon and polyester, so it is easy to get off to the preservation solution inside, followed by the laboratory for the relevant tests.
Sampling swab is a medical device, its production environment and requirements are very strict, there are also quality control standards, the most basic standard of a product is non-toxic and harmless, as well as sampling swab production process in the middle will not produce harmful substances. Why is nucleic acid testing generally oropharyngeal swabs? There are samples from the lower respiratory tract, like sputum, and samples from the upper respiratory tract, like nasopharyngeal swabs and oropharyngeal swabs. Of these swabs, sputum has the highest viral content and the highest positive detection rate, followed by nasopharyngeal swabs, and then oropharyngeal swabs. As an infected person with neocoronavirus, the early stage is dominated by dry cough and sputum is not saliva, which is difficult to obtain. Nasopharyngeal swab collection requires a high level of operation of the sampling personnel, the sampling process is slow, and although the positive rate of detection is higher than that of pharyngeal swabs, they are generally not used for screening of most of the population and can be used for sampling of isolated populations.
Oropharyngeal swabs are easier and faster to sample, so they are generally used for large-scale population screening.
