Beijing News (Reporter Dai Xuan) Yesterday, 11 people in Beijing were diagnosed with new coronary pneumonia, and 10 people completed the transfer. The reporter found that three of them had a negative result when they first received the nucleic acid test, but the antibody was positive. Why is this happening? Does this mean that antibody detection is more "sensitive" than nucleic acid detection? Is it necessary to expand the scope of antibody testing?

Multiple diagnoses confirmed after antibody positive

　　Today, Pang Xinghuo, deputy director of the Beijing Centers for Disease Control and Prevention, announced the details of the 10 newly diagnosed persons yesterday. The reporter found that three people had received nucleic acid tests a few days before the diagnosis, and all were negative, and the serum antibody results were positive. Afterwards, they were transported by ambulance to the hospital for treatment, and then the diagnosis was confirmed.

　　A 51-year-old female patient is a manager of Xinfadi Wholesale Market. Concentrated isolation observation began on June 12, and nucleic acid test results were negative on June 23, and serum antibodies were positive. On June 24, they were transported by 120 ambulances to the Hospital of Integrated Traditional Chinese and Western Medicine in Fengtai District, Beijing. The nucleic acid test was positive on June 25, and the diagnosis was confirmed on the same day. The clinical classification was ordinary.

　　A 25-year-old male patient is located in Tianlun Jincheng, Huaxiang (region), Fengtai District. The work unit is a new wholesale market and is a market operator. Symptoms such as fever and fatigue occurred on June 9, and improved after taking the medicine by oneself. It was transported to a centralized isolation point on June 16 by a special vehicle. On June 23, the nucleic acid test was negative and the serum antibody IgM was positive. On June 24, they were transported by 120 ambulances to the Hospital of Integrated Traditional Chinese and Western Medicine in Fengtai District, Beijing. The nucleic acid test was positive on June 25, and the diagnosis was confirmed on the same day.

　　A 41-year-old male patient is a manager of the Xinfadi wholesale market and works daily in the Xinfadi market or purchases from the Beijing-Shenzhen market. He had a slight cough on June 8 and did not seek medical attention since taking the medicine. On June 16, close contacts as confirmed cases were transported by special vehicle to the centralized isolation point. On June 23, the pharyngeal swab was tested negative for nucleic acid. The blood samples collected were positive for the new coronavirus antibodies IgM and IgG. They were transported by 120 ambulances to the Fengtai District Hospital of Integrated Traditional Chinese and Western Medicine in Beijing. The diagnosis was confirmed on June 25.

Why is the nucleic acid detection of the diagnosed person as negative?

　　An expert from the Department of Infectious Diseases of the Beijing Third Class Hospital analyzed that these three patients should have encountered a "false negative" in the initial nucleic acid test. That is, there is actually a new coronavirus in the patient, but it has not been detected.

　　The reporter learned that the case where the initial nucleic acid test was negative and the subsequent diagnosis was not the first time. Prior to this, some patients with new coronary pneumonia had even tested negative for many times.

　　On February 5, a patient with fever and pneumonia who traveled from Beijing to Beijing was diagnosed with pneumonia by the New Coronavirus in the Department of Respiratory Medicine of the Sino-Japanese Hospital. Before admission, the patient's three throat swabs tested negative for nucleic acid and positive for influenza A nucleic acid. He was admitted to the hospital with severe influenza A. After intubating the ventilator and passing the alveolar lavage test, it was found that the new coronavirus nucleic acid was positive.

　　Why is there a "false shadow"? Jiang Rongmeng, director of the National Infectious Disease Quality Control Center Office, said that in actual operation, the sampling quality, infection time, specimen type, and detection reagents will affect the nucleic acid test results. The positive rate of the following respiratory specimens is significantly higher than that of the upper respiratory specimens. Therefore, a single nucleic acid test cannot be diagnosed or excluded 100%.

　　Are antibody tests more reliable than nucleic acid tests?

　　Obviously infected with the new crown virus, but the nucleic acid test did not immediately give a positive result. Instead, the antibody tested positive. Does this mean that when diagnosing new coronary pneumonia, antibody testing is more "reliable" than nucleic acid testing?

　　The above infection specialists have denied this view.

　　He introduced that although nucleic acid detection is difficult to avoid "false negatives", it can directly detect the presence of new coronavirus in the human body. The positive result is of great significance and is the "gold standard" for clinical diagnosis. Antibody testing is to find out whether there is or has ever had a new coronavirus by looking for antibodies against the new coronavirus in the body. Both detection methods have their pros and cons.

　　The advantage of nucleic acid detection is that it can be applied directly and early. After the patient is infected with the new coronavirus, even if there are no symptoms, the virus gene can be detected to detect whether it is infected. The disadvantage is that there are many links from sampling to detection, and the results are easily affected.

　　Antibody detection is very sensitive, but there is a window period, which lags behind. Antibody IgM can usually be detected 3-6 days after the onset of the disease, and antibody IgG can be detected 10-18 days after the onset of the disease, which does not meet the requirements of early diagnosis. In addition, even if a positive antibody is detected, it does not necessarily mean that the patient is now in an infected state.

　　"Antibody testing can make up for the lack of nucleic acid detection sensitivity, but it cannot replace nucleic acid detection. Of course, according to the latest version of the diagnosis and treatment plan, if both antibodies are positive, it can also be used as a standard for diagnosis." The above experts said.

Should more "sensitive" antibody testing be widely promoted?

　　With the emergence of a new round of local cases in mid-June, Beijing gradually expanded the scope of nucleic acid testing. In Dongcheng District alone, from June 14 to June 25, 620,000 people underwent centralized nucleic acid testing.

　　Because nucleic acid testing "false negatives" occur from time to time, some people wonder whether the scope of antibody testing should be expanded to improve the reliability of screening?

　　"Because Beijing's current extremely low infection rate, antibody testing is used, the cost-effectiveness ratio is too low, it is not necessary. Moreover, any test is not omnipotent, antibody testing will also have'false positives', when conducting a large-scale screening , Especially need to pay attention to this." The above experts said.

　　"Even if there is only one thousandth of false positives, even if there are only 2 million people in Beijing for antibody testing, there will be a misjudgment of 2,000 people. This number has far exceeded the cumulative number of people diagnosed in more than ten days. The significance is not great. It is easy to cause social panic." He said, "The role of antibody testing is mainly to "make up the leaks". For example, fever patients are more likely to be infected with new crowns than ordinary people without a history of epidemiology, so fever clinics have increased. Antibody testing. Antibodies can also provide some clues when the disease control department traces the source.

　　Beijing News reporter Dai Xuan