How is the "false negative" of new coronary pneumonia caused?

[Sally Furniss]

Critical medical expert Wang Chen, academician of the Chinese Academy of Medical Sciences, said in an interview with CCTV on February 5. The positive rate is 30% to 50%. There are still many false negatives by collecting suspected cases of throat swabs. "In other words, more than half of people who are truly infected with the new coronavirus may be" negative ".

"From the perspective of respiratory specimens, alveolar lavage fluid is more sensitive than sputum As a result, the result of sputum is higher than that of the pharynx. Therefore, the more critical patients are, the higher the diagnosis rate is because the alveolar lavage fluid can be collected.

Another key factor is the sensitivity of the kit. They believe that although the viral load will affect the positive rate of the test, it is ultimately the limitation of reagent sensitivity.

more... https://www.yicai.com/news/100495371.html

 

[JJackson]

Thanks Sally, an interesting bit of background.

 

[Pathfinder]

Translation Google

False negatives" are high, so why use a nucleic acid test?
2020
02/11

CCTV News Client

The increase in "false negatives" has brought great challenges to the prevention and control of the epidemic. Is nucleic acid detection reliable?

Many people think that as long as the virus is infected, the nucleic acid test should be positive; if the test is negative, it means that there is no new coronary pneumonia.

However, this is not the case.

Some patients are infected with the new coronavirus, but the nucleic acid test report is negative, and we call this situation a "false negative."

Academician Wang Chen, the dean of the Chinese Academy of Medical Sciences, said in an interview with CCTV on February 5 that the nucleic acid test for new coronavirus infection has a positive rate of only 30% to 50%.

In other words, even in confirmed cases, many are not detected by nucleic acid tests.

The increase in "false negatives" has brought great challenges to the prevention and control of the epidemic. Is nucleic acid detection reliable? Mr. Xiang has compiled many reports and materials such as Nutshell, Beijing News, Doctor Lilac, Southern Weekend, and so on. Let's take a look at whether nucleic acid detection is reliable or not.

What is the new crown pneumonia nucleic acid test?

New crown virus has genetic material. The genetic material of the new 2019 coronavirus is single-stranded RNA, which is its core, most clear and most accurate marker. If the nucleic acid of this new crown virus is detected, then it can certainly indicate that the new crown virus is indeed present.

Why is there a "false negative"?

There is a saying in the inspection discipline, "garbagein, garageout"

Pharyngeal swab sampling in the oral cavity and nasal cavity is the most common sample collection method for new coronary pneumonia testing.

Pharyngeal swab sampling belongs to the upper respiratory tract, but because the new coronavirus is mainly in the deep part of the lung, it is far from the air duct, and the infected person has more dry cough and less sputum, so the upper respiratory tract virus content is relatively low, increasing False negative "probability.

For example, if you use a telescope to look at something outside 1 km, if there are only a few people, you may not see clearly and think that there is no one; but if there are 1,000 people standing there, you can be sure that someone is 1 km away.

The virus, like the person in this analogy, needs to reach a certain amount before the nucleic acid test will show a positive result.

In fact, according to the New Coronary Pneumonia Laboratory Testing Technical Guidelines issued by the National Health and Medical Commission, there are strict requirements on the types, methods, packaging and storage of specimens. Problems at any stage can lead to "false negatives", such as:

Poor sample quality, such as airway samples from oropharynx;

Samples were collected too early or too late;

Improper storage, transportation and handling of samples;

The reason for the technology itself, such as virus mutation.

Do you want to abandon the nucleic acid test when "false negatives" occur frequently?

At present, nucleic acid testing is still the "gold standard" for the diagnosis of new coronary pneumonia.

Gao Zhancheng, director of the Department of Respiratory Medicine, Peking University People's Hospital, said at the State Council ’s joint prevention and control mechanism conference that nucleic acid testing is an indispensable means for the diagnosis of new coronary pneumonia.

Some experts have previously suggested that CT images should be included in the diagnostic criteria due to possible missed tests in nucleic acid testing.

In areas with severe outbreaks such as Wuhan, CT images have been included in the diagnostic criteria.

However, some experts have put forward different opinions. CT is an imaging method for the diagnosis of pneumonia. However, there are many types of viruses that cause pneumonia, not necessarily new coronaviruses, and nucleic acid detection is the etiology of new coronaviruses. Both Can't replace each other.

Of course, there are more accurate genetic sequencing tests, but genetic testing has higher requirements on equipment, bioinformatics teams, costs, and detection cycles. Therefore, nucleic acid detection as a basis for pathogen diagnosis is the most important basis for current diagnosis.

Will "false negatives" cause missed diagnosis?

The biggest problem with "false negatives" is that the infected person was misdiagnosed and went home without any problems, and the family may be infected as a result. As a result, many ordinary people worry that there may be "false negative" patients among the people they contact.

Don't worry too much.

Because the diagnosis and exclusion of cases, in addition to nucleic acid testing, will also be combined with epidemiological history and clinical symptoms and other judgments.

According to the latest diagnosis and treatment plan for new coronary pneumonia issued by the National Health Commission, the diagnosis of cases is divided into suspected cases, confirmed cases and clinically diagnosed cases (only in Hubei Province). Specific analysis factors include:

Epidemiological history (travel history in Wuhan within 14 days before onset, etc.);

Clinical manifestations (fever, imaging features of pneumonia, etc.);

Viral nucleic acid detection, etc.

In short, nucleic acid testing is not the only criterion.

Ding Xinmin, chief physician of the Department of Respiratory Medicine, Beijing Shijitan Hospital, said that the results of nucleic acid testing cannot be used as the sole basis for judgment. At present this is clinically clear. For patients whose symptoms and imaging characteristics are highly suspect, even if the test is negative, further observation is needed.

How to avoid "false negative" release from quarantine?

The National Health and Medical Commission's diagnosis and treatment plan stipulates that there are four requirements for the standard of separation and discharge, including:

Body temperature returned to normal for more than 3 days;

Significant improvement in respiratory symptoms;

Lung imaging showed significant absorption of inflammation;

Negative nucleic acid test for respiratory pathogens twice in a row (sampling interval at least 1 day).

In order to prevent and control the epidemic to the greatest extent, compared with the discharge standards issued by the National Health and Health Commission, the discharge requirements have been increased in many places, including additional testing of fecal nucleic acid detection and extended observation time.

In Hubei, it will take another 10 to 12 days to observe the national standards.

Fecal nucleic acid tests have been added in Shanghai and Zhejiang.

Guangdong also requires patients to have a disease course of 14 days or more before allowing patients to be discharged.

So, instead of saying "negative", you can be discharged. There are many standards that can further reduce the probability of "false negative".

Xiang Xiang said

From a scientific perspective, "false negatives" in nucleic acid testing are inevitable.

In fact, any test can have a "false negative" problem. National and local governments are promulgating various policies to try their best to minimize risks. Experts believe that the entire comprehensive diagnosis and treatment and detection system can completely plug the loopholes.

What you worry about, the country thought of it for you.

If you pay attention to the latest data, you will find that the number of newly diagnosed cases in all regions except Hubei has declined for 6 consecutive days, which means that the prevention and control of the epidemic is moving in a good direction, and the days of spring are coming to us.

http://m.news.cctv.com/2020/02/10/ARTIEk8sHxILfTkshjSMTrJz200210.shtml

 

[Pathfinder]

Translation google

Experts test negative for confirmed patients

2020 at 05:48 on February 11


The epidemic prevention and control situation in the Mainland is still tense. In some places, during the testing period for individual confirmed patients, continuous test results showed "negative" signs. Some medical experts are worried that if the virus mutates midway, it may affect the test results of some patients, and the reagent standards need to be further improved.

Li Yan, director of the laboratory department of the People's Hospital of Wuhan University, said that the current kit is produced based on the virus sequencing of the first batch of patients. If the virus infected by subsequent patients is mutated, some patients' results may not be detected correctly.

She said that for suspected patients, even if the test results are negative, the possibility of virus mutation should be considered. In addition, it is necessary to comprehensively determine whether the patient is infected with the virus, for example, a history of close contact, fever, and changes in CT results.

https://www.singtaousa.com/home/18-即時兩岸/2698311-確診患者檢測多次呈陰性+專家籲完善試劑標準/

 

[Pathfinder]

Apparently no mutation:


Translation Google


Does the virus "escape" the nucleic acid test? Is it a mutation?

February 10, 2020 09:46

In the minds of the people who are concerned about the epidemic of the new crown pneumonia, the new crown virus is really "very cunning". Not only has its transmission method continuously updated, it has evolved from the initial droplet transmission to contact transmission, fecal-oral transmission, and even aerosol transmission. Three patients with negative nucleic acid tests who were eventually diagnosed with new coronary pneumonia also appeared. Does this mean that the new crown virus is rapidly mutating to adapt to the human environment?


Professor Yang Zhanqiu, Professor of the Institute of Virology, Wuhan University Medical College, said that from the current situation, the continuous update of the transmission method of the new crown virus has nothing to do with its mutation, but the result of our deepening understanding of this new virus. Generally speaking, it is impossible for a virus to mutate so quickly. Whether it is Wuhan, Beijing, or Shanghai, the virus samples collected so far are the same, and no mutation has occurred.

So why is there a confirmed patient with a negative nucleic acid test? Gao Zhancheng, director of the Department of Respiratory Medicine, Peking University People's Hospital, said at a press conference on the joint prevention and control mechanism of the State Council on the 9th that the detection rate of any virus's nucleic acid cannot be 100%, and the detection of new type of coronavirus is no exception. It detects False negatives are also inevitable. At the same time, the results of the detection rate are also related to the patient's own severity, different stages of disease development, sampling methods and methods, and the laboratory's own testing conditions.

Yang Zhanqiu said that the nucleic acid detection reagents are not yet complete, and they have not been included in all cases. In addition, the nucleic acid test needs to be detoxified in the patient to detect the virus. The incubation period of the new coronavirus is 2-14 days. During this period, if the patient has not been detoxified or has already been detoxified, it cannot be detected under these circumstances. In addition, the current collection of specimens for nucleic acid testing has limitations. For example, the accuracy of commonly used nasopharyngeal swab tests is low. Because the lesions of new coronary pneumonia mainly occur in the lungs, that is, the lower respiratory tract, sometimes the upper respiratory tract throat can not find the pathogen.

In order to cope with the above situation, Yang Zhanqiu believes that the detection methods need to be further improved, and the current detection methods are also temporary rescue means, which need to be further improved in terms of reliability and sensitivity. In view of this situation, comprehensive judgment should be made according to the clinical symptoms and signs of the patient and other test results such as CT images. Gao Zhancheng emphasized that if the initial negative test result belongs to the suspected case, according to the requirements of the current medical treatment plan of the Health and Health Commission, isolation treatment should be performed in designated hospitals and strictly observed.

https://www.cnbeta.com/articles/tech/941445.htm

 

[Sally Furniss]

According to the website of the State Drug Administration (hereinafter referred to as the State Drug Administration), according to the "Emergency Approval Procedures for Medical Devices", there have been 7 new coronavirus nucleic acid detection reagents that have undergone emergency approval. Recently, there was a report in Beijing China-Japan Friendship Hospital that a patient with negative throat swabs tested for three times was diagnosed as having new coronary pneumonia by testing lower respiratory tract samples.

Why are nucleic acid test results false negative? What are the similarities and differences between the reagent testing products of different companies?

　　Amplification brings new crown virus

　　The genetic material of most organisms is DNA, and the genetic material of only a few viruses is RNA, such as this new crown virus. In order to know whether the human body contains neocoronavirus, human samples need to be collected for testing. According to the "New Coronavirus Infected Pneumonia Diagnosis and Treatment Scheme (Trial Fifth Edition)", the RNA of the new coronavirus can be detected in nasopharyngeal swabs, sputum, lower respiratory tract secretions, blood, feces and other specimens.

　　But in reality, the genetic material of the virus in the sample is extremely traceable. And compared with DNA, RNA is easily degraded. Here comes the problem. The amount of RNA virus in the sample is small and unstable. How can we force this monster to "appear"?

　　Reverse transcription-polymerase chain reaction technology (RT-PCR technology) is a "mirror mirror". The technology can synthesize viral RNA into DNA, then amplify the synthetic DNA, and then detect these amplified products with fluorescent probes. Fluorescent probes are like radars and emit signals as soon as they are locked into the target.

　The more amplified products, the stronger the accumulated fluorescent signal. Nucleic acid detection is to determine the presence of viral nucleic acid in a sample by detecting the accumulation of fluorescent signals. Currently, all approved Newcomer virus nucleic acid detection reagents use RT-PCR technology.

Cheng Jing, academician of the Chinese Academy of Engineering and professor of the Department of Biomedical Engineering of Tsinghua University, said in an interview with reporters from Science and Technology Daily that in addition to RT-PCR, a thermal cycling amplification technology, isothermal nucleic acid sequence amplification technology (NASBA technology) and circular mediator Isothermal amplification technology such as guided isothermal amplification technology (LAMP technology) also plays an important role in the field of molecular diagnostics.

　"At present, the approved nucleic acid detection reagent products have a single indicator, that is, they can only be used to detect a new crown virus." Cheng Jing admitted that for a large number of suspected patients, such detection reagents have limited effects and are clinically useful. There is an urgent need for detection reagent products that can detect multiple pathogens at one time.

　　Approval is simplified, but there should be no fewer processes


In order to cope with the sudden outbreak of new crown pneumonia, the State Food and Drug Administration quickly started the emergency approval procedure for medical devices, speeded up the review and approval process, and expanded the supply of new crown virus nucleic acid detection reagents. After obtaining the RNA sequence of the new crown virus, many companies quickly produced detection reagent products in just a few days, and were quickly approved to supply front-line demand.

　　Yang Rongxi, a professor in the Department of Epidemiology, School of Public Health, Nanjing Medical University, wrote that under normal circumstances, it takes 3-5 years, or even longer, for nucleic acid detection reagents to develop from clinical to clinical. But in an emergency, streamlining processes is what you need.


"Quality inspections and formal clinical trials can be omitted for the time being, but basic R & D processes, a small number of pre-clinical trials, and standardized production are all required."

On February 8th, at a press conference held by the Joint Prevention and Control Mechanism of the State Council, Jiang Deyuan, the inspector of the Device Registration Department of the State Drug Administration, responded to questions about the effectiveness of nucleic acid testing reagents. He said that the approved products have corresponding clinical use experiments, completed product registration inspection, quality management system inspection, submitted clinical evaluation data and corresponding research data, and passed strict approval procedures. Relevant information shows that product performance can meet the technical requirements, and product safety, effectiveness and quality reliability can be guaranteed.

　　Cheng Jing also told reporters: "The test reagents must pass the clinical samples of more than 3 independent medical institutions and issue clinical trial reports. The China Food and Drug Inspection Institute will also test the product performance, give an identification report, and determine whether the test reagent products Satisfy safety, reliability, and effectiveness. These rigid indicators cannot be met. No matter how good the test reagents are in the laboratory, they will not get registration approval. "


　That is to say, although special affairs are handled, the State Food and Drug Administration still adheres to the principles of "unified command, early intervention, follow-up trials, and scientific approval" to ensure that products are safe, effective, and controllable in quality.

　Variations in testing results

　　Doctors at the front line of the epidemic reported that some patients had negative nucleic acid test results, but CT images showed a new type of coronavirus pneumonia, and the condition was constantly developing.


　"Currently, the sensitivity of nucleic acid detection of new coronary pneumonia is only 30% -50%, and missed detection caused by false negatives is a big problem." Zhou Zeqi, chief scientist of Dana (Tianjin) Biotechnology Co., Ltd. told the Science and Technology Daily reporter.

　　Why does my nucleic acid test result false negative?

　　Cheng Jing said in an interview that this may be caused by a variety of factors. "First of all, the development of a kit requires more than a dozen key chemical raw materials, such as enzymes and synthetic DNA. Different suppliers of raw materials selected by different companies will have different enzyme activities and DNA purity, which will affect nucleic acid detection reagents. Accuracy. "Cheng Jing said.


　"In the development of kit products, raw material preparation, production process selection, R & D personnel capabilities, and technical means are used, and every step may cause deviations. Accumulated errors will also cause differences in kit product sensitivity." Cheng Jing Say.

　　Furthermore, irregular sampling procedures can affect subsequent separation and determination results. Taking the most commonly used and easy-to-use throat swab collection as an example, due to the low amount of neocoronavirus in the pharynx, it may cause missed detection. "Although I only took a few swabs on the pharynx, if there is no good professional practice skills, the sample collection location and method may not meet the specifications, which may directly affect the test results." Cheng Jing said, in addition, just after being infected Patients may have a negative test result due to a limited amount of poisoning in the body.


　　Samples must be transported in the cold chain when the samples are sent. If the samples are damaged during the transportation, the test results will also be affected.

　　The problem of false negative results in nucleic acid testing once triggered the call to use CT imaging instead of nucleic acid detection reagents to diagnose new coronary pneumonia. In the recently released "New Coronavirus Infected Pneumonia Diagnosis and Treatment Program (Trial Fifth Edition)", a "clinical diagnosis case" was added in addition to "suspected cases" and "confirmed cases", and "suspected cases have pneumonia "Image features" as its diagnostic criteria (only in Hubei Province), which also means that the CT image results have become the basis for the determination of "clinical diagnosis cases".

　　Professor Zhang Minming, the chief physician of the Department of Radiology of the Second Affiliated Hospital of Zhejiang University and the chairman of the Respiratory Committee of the Radiation Physician Branch of the Chinese Medical Doctors Association, pointed out that there may be misdiagnosis of positive CT images. He also mentioned that cross-infection is likely to occur if CT examinations are ignored without protection. Experts say that neither CT nor nucleic acid tests can guarantee absolute accuracy.

　　"Although nucleic acid testing has a false negative problem, nucleic acid testing is a basis for the diagnosis of pathogens and the most important basis for the current diagnosis." Said Wang Guiqiang, a member of the National Medical Expert Group and director of the Department of Infectious Diseases, Peking University First Hospital.

https://tech.sina.com.cn/roll/2020-0...f1043293.shtml

 

[Sally Furniss]

"Cunning" and "strange" are the first impressions of Lin Bingliang, deputy director of the infection department of the Third Affiliated Hospital of Sun Yat-sen University, on the new crown virus.

Lin Bingliang found that there are still many strange aspects of the new crown virus: patients in incubation period are infectious, asymptomatic patients are also infectious. As an acute respiratory infectious disease, some patients, especially the severe ones, have a longer duration of detoxification ...

Regarding the reasons for the strong transmission of new coronaviruses, Sun Yongchang summarized several points. Including incubation period, it has the ability to spread, so it is contagious for a long time; clinical symptoms are atypical, asymptomatic infection is also infectious; the virus is transmitted in various ways, mainly through respiratory droplets, indirect contact with the mucous membranes of the eyes, mouth or nose There may also be the possibility of aerosol and fecal-oral transmission.

"There are two regions in the coronavirus genome that are highly susceptible to mutation, the genes that encode spike proteins and helper proteins." Sun Yongchang said, because the coronavirus tries to bind to new receptors to escape the immune response, the corona The virus produces a lot of replication errors in these two gene regions, and this will promote the evolution of the virus, eventually leading to the ability of the coronavirus to be transmitted from one species to another.
http://news.shm.com.cn/2020-02/13/content_5014990.htm