On March 12, the State Food and Drug Administration issued a notice approving the application change of the self-test application of new crown antigen products in Nanjing Novizan, Beijing Jinwolf, Shenzhen Huada Inyuan, Guangzhou Wanfu Biology and Beijing Huaketai Biology. Since then, five new crown antigen self-test products have been officially launched.
On March 11, the State Council issued a notice to the Comprehensive Group of the Joint Prevention and Control Mechanism for the Novel Coronavirus Pneumonia Epidemic, deciding to add antigen testing as a supplement to nucleic acid testing, and organized the formulation of the "Application Plan for The Detection of New Coronavirus Antigens (Trial)" (hereinafter referred to as the "Trial Plan").
The pilot plan introduces in detail the application of antigen detection in primary medical and health institutions, the application of antigen detection in isolated observers, and the application of antigen detection in community residents. According to the plan, the use of antigen testing in primary health institutions involves sample collection by professionals, while the application of isolated observers and community residents involves self-testing. This is the first time that the relevant policy of self-testing of new crown for community residents has been clarified.
What is antigen testing?
Can the self-test results replace nucleic acids?
Will vaccination affect antigen test results?
Let's take a look
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What is the principle of COVID-19 antigen testing?
Professor Zhao Wei, director of the Biosecurity Research Center of the School of Public Health of Southern Medical University, introduced that nucleic acid detection measures the genetic material RNA in the new crown virus, and antigen detection measures the protein on the surface of the virus.
Structural proteins of the novel coronavirus include protein S, protein N, protein M, and protein E. Once the body is infected with the virus, these structural proteins can act as immunogens to stimulate plasma cells to produce specific antibodies. These proteins contain multiple antigen epitopes, which can be used to detect the presence of antigens by antibodies that specifically bind to antibodies, thereby proving that there is a new coronavirus in the sample. The sample type of antigen detection reagent is generally a sample of the site of infection, such as an oropharyngeal swab oropharyngeal swab oropharyngeal swab.
What are the advantages and disadvantages of antigen testing compared to nucleic acid testing?
Cai Weiping, chief expert of the Infection Center of the Eighth Affiliated Hospital of Guangzhou Medical University, said that the means of antigen detection are not only used to detect viruses, but also to detect bacteria and fungi. Antigen testing has long been used for rapid diagnosis of diseases such as influenza and AIDS, which is convenient to operate, simple in method, and the results are faster, so that residents can complete sampling and self-testing at home.
The substance of nucleic acid detection of the new crown virus is the nucleic acid of the virus, which is one of the diagnostic criteria for patients with new crown pneumonia, and is currently the main detection method in China. The disadvantage is that the conditions required for testing are higher, requiring medical staff to wear protective clothing to collect samples and send them to a specialized laboratory for PCR amplification, which takes a long time for testing.
Compared with nucleic acid testing, antigen detection is easier to popularize and relatively inexpensive. However, compared with the "gold standard" of nucleic acid testing, its accuracy may be lower, and the probability of missed tests is higher. Therefore, antigen testing is conducive to early detection, but nucleic acid detection evidence is still required to confirm the new crown pneumonia.
Will the antigen test be falsely positive or false negative?
Cai Weiping introduced that under the premise that there is no problem with antigen detection reagents, a positive antigen test indicates that there are corresponding pathogens in the human body, and the carrying amount may be high. Since the sensitivity of nucleic acid detection is higher than that of antigen detection, as long as the antigen is positive, it is very likely that the nucleic acid test is also positive.
False positive means that the tester did not carry the pathogen in his body, but the test result was positive. The probability of a false positive on an antigen test is not high, and on the contrary, it is more likely to have a false negative. False negative refers to missed tests, the tester carries the pathogen, the test result should be positive, but the result is negative. Sometimes the pathogen may not be taken from the upper respiratory tract such as the nasopharynx and oropharynx, or the number of pathogens contained in the sample is small, which may cause false negatives.
Can antigen self-testing replace nucleic acid testing?
No. The notice made it clear that after research, the Comprehensive Group of the Joint Prevention and Control Mechanism of the State Council in response to the novel coronavirus pneumonia epidemic decided to add antigen detection as a supplement to nucleic acid testing. Nucleic acid testing remains the basis for confirming COVID-19 infection.
The "Basic Requirements and Procedures for Self-Testing of New Coronavirus Antigens" in the pilot plan also emphasizes that antigen testing is generally used for sample testing during the acute infection period, that is, within 7 days of the onset of symptoms in suspected people. Both positive and negative antigenic results in suspected populations should be further nucleic acid testing, and positive results can be used for early triage and rapid management of suspected populations, but cannot be used as a basis for confirming the diagnosis of new coronavirus infection.
What are the practical uses of the test results?
The National Health Commission said that antigen testing as a supplementary means can be used for screening specific populations, which is conducive to improving the ability of "early detection". For issues such as whether the results of the self-test of the new crown antigen can be used as travel vouchers, it is not yet clear and still needs to be further refined by the relevant departments.
Zhang Wenhong, head of the Shanghai New Crown Pneumonia Clinical Treatment Expert Group and director of the Department of Infectious Diseases of Huashan Hospital affiliated to Fudan University, said in an interview with the media that there are more asymptomatic infected patients infected with Aomi Kerong, and under the prevention and control principle of pursuing the social "zero clearance", it is necessary to increase the intensity of nucleic acid screening in order to screen out asymptomatic infected people. When nucleic acid collection is inconvenient and resources are insufficient, antigen detection is a good supplement, and through the citizens' home self-test, it helps the relevant departments to find infected people faster and isolate them, and accelerate the realization of social "clearance".
Who can test themselves?
Three groups of people:
- Persons who go to primary medical and health institutions for treatment, accompanied by respiratory tract, fever and other symptoms and have symptoms within 5 days;
- Quarantine and observation personnel, including personnel in home isolation observation, close and sub-close contact, entry isolation observation, sealing and control area and control area;
- Residents of communities with antigen self-testing needs.
How to determine the frequency of the new crown self-test?
Depending on the crowd. For isolated observers, nucleic acid testing is carried out in accordance with the requirements of the current relevant prevention and control programs during the isolation and observation period, and antigen self-test is carried out once a day for the first 5 days.
For community residents, those who have self-testing needs can purchase their own self-tests. Asymptomatic residents with negative antigen tests can be closely observed and then undergo antigen testing or nucleic acid testing when necessary; symptomatic residents are recommended to go to a medical institution that has set up a fever clinic as soon as possible for nucleic acid testing; if it is inconvenient to seek medical treatment, they should self-isolate at home, avoid going out, and conduct antigen self-testing once a day for 5 consecutive days.
Will vaccination against COVID-19 affect antigen testing?
Cai Weiping said that after receiving the inactivated vaccine of the new crown virus, followed by the antigen test of the new crown virus, false positives may occur. It is generally not recommended that residents have an antigen test within 24 hours of vaccination.
Have you been infected with the new crown virus before, does it affect the antigen test results?
Antigen testing is minimally affected by previous infections. If you have been infected with the new crown virus but the virus has been removed from the body, the antigen test result will be negative.
What are the precautions for self-testing?
There are three major steps to antigen self-testing.
First, prepare before antigen self-testing.
1. Wash your hands. Wash your hands with running water or hand sanitizer.
2. Understand the testing process. Carefully read the antigen self-test agent supporting instructions and antigen self-test related precautions.
3. Reagent preparation. Check whether the antigen self-test agent is within the shelf life, and check whether the contents of nasal swabs, sampling tubes, test cards, etc. are missing or damaged. If the reagent is expired or the reagent contents are missing or damaged, the detection reagent should be replaced in time.
4. Confirm the environmental temperature and humidity requirements for testing. Colloidal gold test strip detection generally requires that under the condition of 14 °C-30 °C normal temperature, to avoid excessive cold, overheating or excessive humidity leading to abnormal test results. Antigen detection card is placed in a flat, clean place after unpacking.
Second, sample collection.
1. For those over 14 years old, nasal swabs can be taken by themselves. The self-examiner first blows off the snot with toilet paper. Carefully unpack the nasal swab and avoid hand contact with the swab head. Then the head is slightly tilted, one hand holds the swab on one side of the nostril, slowly deepens backwards along the bottom of the lower nasal passage for 1-1.5 cm, rotates the nasal cavity at least 4 times (stay time is not less than 15 seconds), and then repeats the same operation for the other nasal cavity using the same swab.
2. Self-testers aged 2-14 should be sampled by other adults. For sampling, blow the nose off with toilet paper and then tilt your head slightly. The sampler carefully unpacks the outer packaging of the nasal swab, avoid contact with the swab head with the hand, gently support the head of the person being collected with one hand, hold the swab on one side of the nostril in the other hand, slowly go back 1 cm along the bottom of the lower nasal passage and rotate the nasal cavity for at least 4 turns (the stay time is not less than 15 seconds), and then repeat the same operation for the other nasal cavity using the same swab.
Third, antigen detection.
1. According to the reagent instructions, the nasal swab after the sample is collected is immediately placed in the sampling tube, and the swab head should be rotated and mixed in the preservation solution for at least 30 seconds, and the swab head is squeezed at least 5 times by hand across the outer wall of the sampling tube to ensure that the sample is fully eluted in the sampling tube.
2. Squeeze the swab head liquid dry by hand across the outer wall of the sampling tube, and discard the swab. After the sampling tube is covered, drop the liquid vertically into the test card sample well.
3. According to the reagent instructions, wait for a certain period of time to interpret the results. Positive results: Red or purple bands are shown at both "C" and "T", and the bands at "T" can be dark or light, and both are positive results. Negative results: a red or purple band appears at "C" and a band is not shown at "T". Invalid result: No red or purple bands appear at "C", regardless of whether stripes appear at "T". The results are invalid, and the test strip needs to be re-tested.
What to do with used self-test agents?
The same is divided into groups.
Isolation observer: Whether the test result is negative or positive, all sample swabs, sampling tubes, test cards, etc. after use are loaded into sealed bags by the management personnel with reference to medical waste or according to procedures.
Community residents: If the test result is negative, all nasal swabs, sampling tubes, test cards, etc. after use are loaded into a sealed bag and disposed of as general garbage; if the test result is positive, it will be handed over to the medical institution for treatment according to the medical waste when the personnel are transferred.
Source: Guangzhou Health Commission
EDIT: Dream Circle