The new crown virus nucleic acid detection 11 times before the sun, why?

January 4, Dalian Xinguan pneumonia outbreak prevention and control work press conference, the relevant officials said that some cases (New Crown Pneumonia confirmed) did 11 nucleic acid tests before finally testing positive.
nucleic acid detection has long been considered the most effective "mirror", using molecular biology techniques to "show" invisible viruses.
why do some people not come out 1 time, it takes 11 times? With questions, the Science and Technology Daily reporter interviewed Liu Xiangxuan, director of the inspection department of Tongren Hospital in Beijing, affiliated with Capital Medical University.: Of course not. Generally speaking, the new coronavirus can be found in the human respiratory tract endocyste cells in about 96 hours, can be collected by pharynx swab samples for the new coronavirus nucleic acid testing. It has been reported in the past that not all new crown patients can test positive for nucleic acid.
, why test for nucleic acid 11 times in a row for a case? This is mainly from a laboratory point of view, the highly suspected cases of whether or not infected with the new coronavirus confirmation.
time, 11 tests cover the detection cycle of viral infection, which can theoretically be measured. However, 10 negatives may be related to the testing performance of the kit, but also to the individual new coronavirus load, sampling site, sample amount, sampling level, as well as laboratory testing conditions and personnel operation, the reasons are very complex. Do not rule out individual special cases, the viral load is very small, may not be detected, the result has been negative.: carrying the virus but can not detect, we call the detection of "false negative." The whole test includes sampling, transportation, inactivation, nucleic acid extraction, PCR reaction and many other steps, each link of the wrong operation may lead to "false negative."
the "false negative" results we are currently testing, mainly because the collection of specimens is not qualified. The use of ordinary cotton swabs certainly can not, to plant velvet swabs. Whether collecting nasopharyngeal swabs or pharynx swabs, mainly to collect relatively high levels of virus pharynx secretions, repeated application, scraping out enough, wrapped in virus skin cells. Such as mouth swab collection, many people open their mouths, the collection staff did not use the tongue plate, just in the mouth and pharynx a wipe, collection is not correct.
In fact, for specimen collection, the Nucleic Acid Detection Work Manual clearly states that respiratory samples, including upper respiratory tract specimens (preferred nasopharyngeal swabs, etc.) or lower respiratory tract specimens (respiratory absorbents, bronchophary irrigation lotions, alfur gas, deep cough sputum, etc.) should be collected. Among them, severe cases give priority to the collection of lower respiratory tract specimens;: Five words in general: people, machines, materials, law, rings. "People" are easy to understand, and trained technicians are key. This is the same in every line, some sales staff "one catch", and the operation of the tester should also do training in place. "Machine" refers to the use of nucleic acid testing equipment to meet the requirements, such as calibration, "material" refers to the test reagent to have performance verification, such as during the shelf life, according to the kit preservation, etc. , "law" refers to the operating specifications to comply with the standardized process, can not be oscillation, mixing and covering any link, "ring" refers to the detection environment to meet the requirements, such as temperature and humidity, can not interfere with the test results of the substance.