Some ideas on the mathematical model of COVID-19 epidemic

 Some ideas on the mathematical model of COVID-19 epidemic

       Next, we will use the data of suspected cases to make predictions. The reasons are as follows:

  •  Clinical diagnosis will be included in the number of confirmed cases, which means that the number of confirmed cases is disturbed, and the degree of interference is very large~
  • Confirmed cases come from suspected cases. In the diagnosis and treatment plan for pneumonia caused by novel coronavirus infection (trial version 5), the “clinical diagnosis” is added to the case diagnosis classification of Hubei Province. The clinical diagnosis is from the suspected cases, and the confirmed cases are from the clinical diagnosis and the suspected cases.
  • The diagnosis process of confirmed cases is limited by hardware conditions (such as the number of nucleic acid reagents and other medical equipment), and the number of missed cases should be large; The criteria for judging suspected cases are lower. As long as their epidemic history and whether they have fever, the number of missing cases should be less.

Therefore, we will use antigen detection to judge suspected cases for subsequent prediction.

Step 1: capture data

      From Tencent’s real-time epidemic data, we captured the daily increase data. The captured results are as follows:

Step 2: estimate the actual number of confirmed cases

We need to do the following:

  • Estimate the proportion of confirmed cases in suspected cases
  • Determine the number of confirmed patients according to the daily increase data
  • According to the SI model, determine the final confirmed number and the approximate time of the end of the epidemic

We will first look at how to estimate the proportion of confirmed cases in suspected cases through existing data.

Second, we determined the number of confirmed cases according to the daily increase of suspected cases.

  • To determine the total number of suspected cases per day, we need to accumulate and function cumsum ()
  • To determine the total number of confirmed cases per day, we only need to multiply 0.5960971132108407 by the total number of suspected cases per day

     It can be seen that our predicted total number of confirmed cases per day is higher than the official one, but it has started to overlap in recent days. In fact, it can be understood that under the current state’s high attention and full publicity, individuals and governments at all levels no longer hide information, so it can be considered as true data.

     If all suspected cases are turned into confirmed cases, the total number of actual infections is more than 70000, as shown by the green line~

Prediction and analysis of the spread of COVID-19

 Prediction and analysis of the spread of COVID-19

1. Traditional model

1.1 prediction and analysis of COVID-19 epidemic spread based on SIR model

The model is established by differential equations. First Δ t \Delta t Δ Number of new patients in t:

     The first item describes the number of uninfected persons transmitted from infected persons to uninfected persons at time t , which is interpreted as the number of uninfected persons contacted by the total number of infected persons at the daily contact rate, and becomes the number of uninfected persons transmitted from infected persons to uninfected persons at time t  (therefore, it should be multiplied by s (T) ; The second item describes the infected person cured at the time of T; The third item describes the infected person who died at the time of T.

     Remove n from the above expression, divided by Δ t  and taking the limit, the following limit equation can be obtained:

      It can be used to analyze the change law of each proportional variable with time

     Of course, the biggest highlight of this article is that the function of y about s is written according to the limit equation, the derivative of the function and the standing point are determined, and the following laws are determined. 

2.Modeling ideas

       In our problem, we are facing a non closed dynamic problem, that is, the population of a region is not fixed, and there are inflow and outflow. The specific form is shown in the following figure:

          The idea now is that these two quantities are not used as modeling variables, but rather to control the initial values of S and e at each time. Both the input population and the output population include the possibility of S and E, but their proportions are affected by: the degree of control ( whether the 48 hour nucleic acid certificate is required)

Radiological findings from 81 patients with COVID-19 pneumonia inWuhan, China: a descriptive study”

 Radiological findings from 81 patients with COVID-19 pneumonia inWuhan, China: a descriptive study”

       81 patients were admitted from December 20, 2019 to January 23, 2020. There were 42 males and 39 females with an average age of 49.5 years.

     CT showed that 81 cases of pulmonary lesions involved an average of 10.5 lung segments, including 2.8 lung segments in subclinical stage, 11.1 lung segments in 1 week, 13.0 lung segments in 1-2 weeks, and 12.1 lung segments in 2-3 weeks.

    The subclinical stage (n = 15) mainly showed unilateral and multicentric ground glass shadow (93%).

     Within one week after the onset of symptoms (n = 21), the lesions were mostly bilateral and diffuse ground glass shadows (81%).

     The symptoms appeared for 1-2 weeks (n = 30), the ground glass shadow continued to decrease (57%), and most of them were consolidation and mixed lesions (40%).

     The symptoms appeared for 2-3 weeks (n = 15), and the ground glass shadow was significantly reduced (33%), mainly including consolidation and mixed lesions (53%).

    Chest CT of patients with COVID-19 showed pulmonary infiltrative lesions, even in asymptomatic patients.

    Within 1-3 weeks after the onset, the lesion rapidly progressed from unilateral and focal lesions to diffuse ground glass shadows in both lungs, and consolidation in the later stage.

    The results showed that the virus load in throat swabs and sputum samples reached a peak about 5-6 days after the onset of symptoms, from 104 copies per ml to 107 copies.

    This change pattern of viral load is different from that of SARS, which usually reaches its peak around 10 days after the onset of the disease.

   The viral load of sputum samples is usually higher than that of laryngeal swabs.

     Viral RNA was not detected in urine or stool samples of two patients.

      Subsequently, the study group analyzed the respiratory tract samples (1 nasal swab, 67 pharyngeal swabs and 42 sputum) of 80 patients with different infection stages.

         The viral load of these samples ranged from 641 copies per ml to 1.34 × 1011 copies, with a median of 7.99 for pharyngeal swab samples × 104, the median of sputum samples was 7.52 × 105。

       The only nasal swab was collected 3 days after the onset of the disease, and the viral load was 1.69/ml × 105 copies.

        Overall, the viral load in the early stage of onset was high (> 1 × 106 copies).

       However, one deceased patient had the highest viral load in sputum samples on day 8 after onset, at 1.34 × 1011 copies.

      It is worth noting that two people received positive tests due to their contact history. The results showed that the virus was positive on the day before the onset of the disease, indicating that the infected individuals had been infectious before the onset of symptoms.

     Among the 30 pairs of throat swabs and sputum samples available, there was a significant correlation between the viral load of the two samples on days 1-3, 4-7 and 7-14.

    Of the 17 confirmed cases of novel coronavirus infection (0-13 days after onset), 9 patients had positive stool tests.

    The viral load in feces ranged from 550 copies per ml to 1.21 × 105 copies, lower than the respiratory tract samples, and precautions should be taken when handling fecal samples.

A new novel coronavirus saliva detection technique that is more accurate and easier than nasal swabs

 A new novel coronavirus saliva detection technique that is more accurate and easier than nasal swabs

       Since the outbreak of the epidemic, the detection technology of novel coronavirus has made rapid progress. However, at that time, people had to go to the hospital for a nasal swab test that was deep enough to “make the brain itch”, and waited for several days to get the results.     Now, the University of Illinois at Urbana Champaign (UIUC), Yale  University,       Rockefeller University and other universities have independently developed a series of saliva based detection technologies. These tests are less invasive, faster to process, and in some cases more sensitive than nasal tests.

       “Although nasal swabs may not be practical in daily use, it is quite easy to provide saliva samples repeatedly,”      said Rebecca Lee Smith. He is the infectious disease epidemiologist of UIUC and the scientific adviser of covidshield project, which is the nucleic acid detection project conducted by Brennan.

       Covidshield is a polymerase chain reaction (PCR) detection, which is a highly sensitive molecular detection method. It can amplify the genetic material of sars-cov-2 (a novel coronavirus causing covid) to a detectable level. PCR analysis is usually performed in the laboratory, but not all.

           After the covidshield saliva sample is delivered to the laboratory, the scientists will put it into a hot tub to kill any existing virus and neutralize saliva components that may interfere with the detection. Then the sample can be amplified. First, “primers” (short fragments of genetic material) are added to the sample. As Smith explained, primers are “a little ‘idea’ of the virus at the RNA [genetic material] level”. RNA from the virus is converted into complementary DNA (cDNA). Finally, the primer will connect itself to the cDNA of the virus and replicate. As this process continues, all cDNAs will be continuously amplified until positive samples can be easily identified and detected.

           Covidshield’s method discards the traditional RNA extraction step and uses heating and chemical treatment to release viral RNA. This enables test developers to promise to provide test results within 24 hours. According to Beth Heller, a spokeswoman for shield Illinois, a nonprofit Department of the University of Illinois system, the average turnaround time can be even shorter. “From sample collection to providing test results, we now spend an average of 13 hours,” Beth Heller said.

           The time difference between receiving the coronal test and obtaining the results is a key indicator to evaluate the diagnostic method. In addition to the sensitivity of the overall detection, this is also part of the extensive debate about the use of PCR and rapid antigen detection. Antigen detection is mainly based on nasal swabs, although researchers are working to develop an accurate version based on saliva. Antigen detection is to detect the presence of viral antigens by using a special test paper, and viral antigens are viral fragments that cause immune reactions.

         Proponents of antigen testing believe that its advantages of speed and low cost make it more suitable as a public health tool. Epidemiologist Michael Mina believes that PCR testing should really be reserved for medical research, especially those tests that must be sent to the laboratory, and should not be used, for example, when doctors diagnose patients. She is currently the chief scientific officer of emed, and has also provided testing advice to US President Joe Biden and his government. The antigen testing methods sold by the company have been certified through the telemedicine platform.

         The hypersensitivity of PCR detection is one of the main problems in public health. Mina said: “I don’t want someone to test positive when they are no longer infectious, because if they are positive, I will tell them that they will be isolated for 10 days; if they are no longer infectious and are isolated for 10 days, it will be harmful to public health.”

         However, Smith believes that saliva based PCR detection and antigen detection are very different in use cases. Her research team provided the Centers for Disease Control and prevention with strategies on how to use antigen testing. “Saliva based PCR tests are very sensitive and they can actually detect infection before you get infected,” Smith said They are as sensitive or even more sensitive as PCR detection of nasal swabs. This may be particularly effective for the Omicron variant because it replicates more in the mouth and throat than the previous variant.

         Smith explained that even if someone is no longer infectious, the PCR of his saliva may still show positive due to the sensitivity of the technology. At this point, antigen testing may be more appropriate to determine when someone is no longer infectious. She added: “I do not recommend any PCR (detection) for withdrawal from isolation, but antigen testing may be very useful in this regard.”

        In the early stages of the pandemic, saliva based covid testing required recourse to healthcare professionals. But covidshield and other recently developed saliva testing technologies make testing easier. And this availability has also begun to extend to families: the US Food and Drug Administration (FDA) has approved several emergency use authorizations for self-collection and saliva based PCR testing technology, including a test using covidshield technology. “Self collection” refers to self collection of saliva without the presence of a trained observer. Although they still need to be transported to the laboratory for analysis, this avoids the need to go to the testing site and makes it possible to collect samples at home. According to David Clark, CEO of shield T3, a subsidiary of the University of Illinois systems, the company has recently started to produce covidshield self collection kits, which include all the materials needed to provide samples and send them to the laboratory for testing collection points. Clark said that shield T3 is currently providing kits to schools, universities and some companies on a limited basis. Eventually, he and his team envisioned distributing these kits through vending machines or in the workplace.

Let’s talk about the coronavirus test

 Let’s talk about the coronavirus test

      Why should re sampling be conducted for recheck if the initial screening is positive?

      The covid-19 nucleic acid test must go through two processes: the first is the first test (primary screening) of the testing institution. If the result is positive, the person will be considered as the primary screening positive person. Step 2: all positive samples of primary screening need to be rechecked by higher qualified institutions to ensure that each result is accurate.

      After resampling and repeated testing, it may be determined that the coronavirus nucleic acid is positive, or the retest result may be negative, “suspicious samples” are excluded. Generally, there are two possibilities for suspicious samples: one is that CT is located in the gray area, and the other is that a single target gene of the virus appears positive due to some unexpected circumstances.

     The purpose of initiating emergency response in the event of a first screening positive person is to make full use of the golden 4-hour emergency response time after receiving the report, to prevent and control the whole chain accurately and quickly, and to control the epidemic in the bud as much as possible.

     Why do some people have positive nasal swabs? Pharyngeal swab negative? Even a anal swab?

     Since novel coronavirus is transmitted through the respiratory tract, it has different clinical significance to collect samples from different parts. In addition to the well-known nasal swabs and pharyngeal swabs, sputum, blood and anal swabs can also be collected:

Nasal swabs and pharyngeal swabs – upper respiratory tract specimens

Sputum – lower respiratory tract specimen

Anal swab – alimentary tract specimen

Blood – antibody test specimen

         The viral load of upper respiratory tract specimens (nasopharyngeal swabs and oropharyngeal swabs) is high in the first 1-3 days of clinical symptoms, and begins to slowly decrease after a week. The viral load of lower respiratory tract specimens (sputum) usually reaches a peak within 2 weeks after the onset of the disease, and the viral load is higher than that of upper respiratory tract specimens. The viral load of stool samples usually reaches a peak in 2-3 weeks after the onset of the disease, and the overall viral load is lower than that of sputum samples, The antibody in the serum can be detected after one week, and it can also determine whether there has been infection in the past.

       Therefore, in the recent cases, it is mentioned that the patient has infection symptoms, but the respiratory tract specimen is negative for coronavirus nucleic acid, multiple collection can be carried out at multiple points and locations.

       For example, the New England Journal of Medicine recently published an article describing the relationship between the viral load of nasal swabs and pharyngeal swabs and the disease progression, revealing the dynamic changes of the viral load of novel coronavirus after the onset of symptoms. In the early stage of COVID-19, the viral load was high and then gradually decreased.

       Why is there an acid positive condition in the antigen negative nucleus?

        twenty-three thousand one hundred and fifty-one trillion and six hundred and fifty-two billion three hundred and forty-six million five hundred and twenty-three thousand four hundred and thirty-six

        A review on lancet in February 2022 indicated that antigen detection and RNA detection occur within 0-7 days of infection. The sensitivity of antigen detection is far lower than that of RNA detection. Antigen detection can only detect 105-106 copies, while RNA detection can reach 102-103 copies. Antibody detection usually occurs 7-14 days after infection and includes IgG and IgM.

       It can be seen that when the viral load is small, the antigen cannot be detected, but it can be detected by high-sensitivity RNA detection. This is the reason why the antigen is positive. It also explains why the CDC recommends that antigen and RNA detection complement each other.

    How long will there be a positive to negative change? 

      seventy-seven thousand four hundred and fifty-one trillion and six hundred and fifty-two billion three hundred and forty-six million five hundred and twenty-three thousand seven hundred and twenty-one ertain, but it will turn negative within one week.

       The influencing factors of negative conversion are complex, including the autoimmune system, whether there are basic diseases, and the vaccine situation. Among them, the immune system is like the bodyguard of the human body. When the immunity is strong, the virus is weak, and it may recover quickly. Maybe after a sleep, it will turn positive to negative; When the immunity is weak, the virus is strong and needs a period of time to recover.

      It is precisely because of the complex tug of war between the virus and the immune system that regular intensive sampling and detection are needed to monitor the progress of the disease in real time.

Should the sampling swabs used for coronavirus nucleic acid detection and antigen detection be sterilized? Why does it turn yellow?

 Should the sampling swabs used for coronavirus nucleic acid detection and antigen detection be sterilized? Why does it turn yellow?

       In the current epidemic situation, the detection of covid-19 nucleic acid and antigen is indispensable. I believe everyone has a lot of contact with the small sampling swab during nucleic acid and antigen detection. However, many people are still worried about whether the small sampling swab has been sterilized. Why does the swab turn yellow and will it affect us?

       Sampling is the first step of testing. Many friends have questions about whether the disposable sampling swab is “sterilized” or “non sterilized”, and whether it needs to be sterilized. Let’s take a look at these questions

1. What material is generally used for sampling swabs?

      Disposable collection swabs are different from cotton swabs used in daily life and belong to medical device products.

      Common sampling swab head materials include flocking, sponge, etc. It shall have the characteristics of easy elution, no toxic effect on pathogens and contacted cells and tissues, and no impact on subsequent detection.

2. What is “sterile” and what is “non sterile” / “non sterile”

       [sterility]: refers to the state without viable microorganisms. After sterilization, the theoretical probability of the existence of viable microorganisms should not exceed the negative 6th power of 10. Therefore, in some use environments with high requirements, “sterile” medical devices are required.

       [non sterile / non sterile]: Although this kind of medical devices can not be as strict as “sterile” medical devices, which are almost “free of bacteria”, they are not “dirty”. All medical devices must meet certain health requirements, such as strictly controlling the number of microorganisms, before they can be qualified for marketing.

      The sampling head is the core part of a disposable sampling swab. Take it as an example, the sampling head of a common cotton swab can be made of medical absorbent cotton, polyester staple fiber, electrostatic flocking fabric and other materials. If the “non sterile” medical absorbent cotton is used, it must comply with the Chinese pharmaceutical industry standard medical absorbent cotton. The manufacturer must provide the microbial limit for the reference of medical institutions and other users.

3. Will the sampling swab with “bacteria without sterilization” affect the antigen detection?

      This is a misunderstanding caused by confusing bacteria and viruses.

      It should be noted that the antigen detection “looks for” the N protein of novel coronavirus carried by the covid-19 infected person. The display window of the reagent strip contains an antibody that can recognize the viral protein, which is like a dam. It can only intercept the antibody latex / colloidal gold conjugate that binds to the viral antigen, and present it in the form of antibody antigen antibody latex / colloidal gold (referred to as double antibody sandwich method) so as to develop color in the display window. Therefore, even if the sampling swab carries “bacteria”, the detection reagent card will “ignore” and focus on finding the N protein of novel coronavirus carried by the coronavirus infected person. Since the reagent card is not interfered by “bacteria”, the result of antigen detection will not be affected.

4. Is it necessary to sterilize the “non sterilized” / non sterilized “sampling swabs before use?

      It is not recommended to use household disinfectant to disinfect the sampling swab head. The disinfectant may have the risk of destroying the sampling sample, thus affecting the original test results. The sampling swab is a medical device product, which is used to scrape the cells and virus samples into the extraction solution / virus preservation solution for relevant detection. The qualified sampling swab is non-toxic and harmless.

5. Why are some sampling swabs “yellow”, and how is it caused?

      As mentioned above, some sampling swab heads are made of sponge (also known as polyurethane foam), which will cause thermal oxidation yellowing under light (UV) and high temperature conditions or gas fumigation yellowing caused by contact with nitrogen oxides (NOx) in the air due to the characteristics of the swab materials. This is an inevitable phenomenon in the current production process of polyurethane foam, so it is recommended to store it at 2-30 ℃ away from light to avoid or slow down yellowing.

Sampling swabs and nucleic acid detection, antigen detection cotton swabs, and their sterilization are briefly introduced

 Sampling swabs and nucleic acid detection, antigen detection cotton swabs, and their sterilization are briefly introduced

      We should all know whether we are infected with novel coronavirus. In addition to nucleic acid, we can also use antigen self-test. The sampling swab and cotton swab used for testing are common medical devices.

      Brief introduction of swab sampling with cotton swab for nucleic acid detection and antigen detection

   the sampling swab can be used to collect oral epidermal cells or nasal virus samples, and then the cells or samples are stored in the collection tube and transferred to the laboratory for testing, so as to realize the detection of human oral or nasal diseases. Different from the cotton swabs used in daily life, the sampling swab shall ensure the sampling amount and release amount, and the selected materials shall not affect the subsequent detection. The swab is mainly composed of a sampling head and a medical ABS plastic rod. The material of the sampling head is closely related to the subsequent detection.

       Flocking swab made of nylon fiber through spray technology.

   the sampling swab head should be made of polyester (PE) synthetic fiber or rayon (artificial fiber), and calcium alginate sponge or wooden swab (including bamboo swab) cannot be used. The swab head should not be made of cotton products, because cotton fiber has strong adsorption on protein and is not easy to elute into the subsequent preservation solution; However, the broken wooden stick or bamboo stick containing calcium alginate and wood components will also absorb protein when soaked in the preservation solution, and even inhibit the subsequent PCR reaction. 

        Brief introduction of nucleic acid detection, antigen detection, swab sampling and swab sterilization

   sampling swabs are usually sterilized by EO (ethylene oxide sterilization) or irradiation, but EO, as a carcinogen, is extremely harmful to human health. For EO sterilized swabs, some people worry about whether EO will remain on the swabs and enter the human body during detection. However, there is no need to worry. The EO sterilized swabs will be analyzed for 14 days, and the EO residue can only be delivered after passing the test. Moreover, it will be naturally analyzed during the circulation process. The EO residue of the sampling swabs that reach our hands will not affect human health.

       How to correctly select a disposable virus sampling tube? Pay attention to the following aspects:

1. Swab

   flocking swab, as a sample collection tool, has the advantages of high sample collection rate, good adsorption and not easy to shed wool, which is not available in cotton swabs, and can collect samples well.

2. Virus storage tube

   general name of virus sampling tube disposable virus sampling tube is generally used for the detection and sampling of infectious pathogenic microorganisms by disease control departments and clinical departments. It is applicable to the detection and sampling of influenza virus (including general influenza, highly pathogenic virus, influenza A (H1N1), hand, foot and mouth virus, novel coronavirus, measles, rubella and other types of viruses. VTM virus sampling tube can also be used for detection and sampling of mycoplasma, chlamydia and Ureaplasma urealyticum.

       Generally, the virus sampling tube is equipped with a disposable flocking swab. From the appearance, the flocking swab is white and soft. Using this soft brush during the sampling process will make the user feel no foreign matter, and it is suitable for people sampling at different parts. Moreover, the flocking swab is designed with a break point that conforms to the length of the sampling tube and the natural lumen of the human body, which is not only convenient for sampling but also convenient for specimen transportation.

   the virus sampling tubes are loaded with infectious substances, and some are even highly pathogenic substances. Therefore, the requirements for packaging containers are very strict, and the requirements in three aspects should be met at the same time

(1) Transportation safety.

   ensure that the sample does not leak during transportation. Sampling tubes complying with who regulations and biosafety regulations.

(2) , security of storage.

   ensure that the sample does not leak during storage. Sampling tubes complying with who regulations and biosafety regulations.

(3) . validity of samples.

   ensure that the sampling tube itself will not have toxic effects on the sample.

How to correctly select a disposable virus sampling tube?

 How to correctly select a disposable virus sampling tube?

        With the ravage of delta, a large-scale nucleic acid test has been started in China. However, only the complete collection and non-destructive preservation of samples in large-scale nucleic acid test can enable the tester to make an accurate judgment on the infection of novel coronavirus in the person to whom the sample belongs. How to collect and preserve samples intact?

         How to correctly select a disposable virus sampling tube? Pay attention to the following aspects:

1. Swab

   flocking swab, as a sample collection tool, has the advantages of high sample collection rate, good adsorption and not easy to shed wool, which is not available in cotton swabs, and can collect samples well.

2. Virus storage tube

   general name of virus sampling tube disposable virus sampling tube is generally used for the detection and sampling of infectious pathogenic microorganisms by disease control departments and clinical departments. It is applicable to the detection and sampling of influenza virus (including general influenza, highly pathogenic virus, influenza A (H1N1), hand, foot and mouth virus, novel coronavirus, measles, rubella and other types of viruses. VTM virus sampling tube can also be used for detection and sampling of mycoplasma, chlamydia and Ureaplasma urealyticum.

        Generally,  the virus sampling tube is equipped with a disposable flocking swab. From the appearance, the flocking swab is white and soft. Using this soft brush during the sampling process will make the user feel no foreign matter, and it is suitable for people sampling at different parts. Moreover, the flocking swab is designed with a break point that conforms to the length of the sampling tube and the natural lumen of the human body, which is not only convenient for sampling but also convenient for specimen transportation.

      The virus sampling tubes are filled with infectious substances, and some are even highly pathogenic substances. Therefore, the requirements for packaging containers are very strict, and the requirements in three aspects should be met at the same time:

 (1) safety of transportation.

Ensure no leakage of samples during transportation. Sampling tubes complying with who regulations and biosafety regulations.

 (2) security of storage.

  ensure that the sample does not leak during storage. Sampling tubes complying with who regulations and biosafety regulations.

(3) . validity of samples.

       Ensure that the sampling tube itself will not have toxic effect on the sample.

  3. Virus preservation solution

   as the core of the sampling tube, virus preservation solution can be divided into two types, i.e. inactivation type and inactivation type. Inactivated preservation solution needs to ensure the safety of laboratory personnel and prevent the second spread of virus; In addition to the above-mentioned characteristics, the preservation solution of keeping alive also needs to have the characteristics of being able to store for a long time in a wide temperature range, and the virus nucleic acid is not easy to be degraded, so as to maintain the biological characteristics of the virus to the maximum extent.

4. Packing form:

   in terms of packaging form, Shenzhen medico Biomedical Technology Co., Ltd. makes use of its own advantages to fill the preservation solution in the clean workshop meeting GMP standards, and uses disposable easy to tear packaging to avoid pollution and improve product quality and performance. Before the products leave the factory, irradiation sterilization is also carried out to ensure that the ex factory products will not cause pollution to the samples and avoid affecting the final test.

The magic “red line” — a brief introduction to the principle of novel coronavirus antigen detection

 The magic “red line” — a brief introduction to the principle of novel coronavirus antigen detection

Morphological structure of novel coronavirus

The virus is like a mixed jelly wrapped in a gum.

       Rubber candy sandwich “is located in the center of the virus body, and the main component is nucleic acid (ssRNA), which provides genetic information for the replication, inheritance and variation of the virus. The outer layer of “soft candy” is the protein shell of the virus body, called “nucleocapsid” (n), which can protect the virus nucleic acid from external factors and mediate the virus to enter the host cell. Before the entry, the “sugar coating” wrapped around the “soft candy” can be understood as the envelope of the virus body, which is a double-layer membrane wrapped around the nucleocapsid of the virus.

      This layer of “sugar coating” of novel coronavirus is extremely gorgeous. Its membrane contains spike glycoprotein (s), envelope protein (E) and membrane protein (m)

What does the “novel coronavirus antigen test” detect?

      Among these structural proteins, N protein is highly conserved among different sars-cov-2 virus strains and has good immunogenicity. It is the structural protein with the highest expression after the virus infects cells and is a good biomarker for detection. At present, the antigen detection of novel coronavirus is mainly based on the detection of N protein

Principle of antigen detection of novel coronavirus

     A white board, drop several drops of liquid into the sample hole, why can there be a magic “red line” after a few minutes?

     This antigen detection technique is called “colloidal gold method”. Take the novel coronavirus (2019 ncov) antigen detection kit that has been listed in China as an example, let’s take a “shallow” look at the formation process of the “red line”.

     It is assumed that this is a oropharyngeal / nasopharyngeal swab with novel coronavirus specific antigen (N protein). After the swab treatment solution is released and eluted, the N protein is dropped into the sample well with the treatment solution.

      The sample to be tested flows from one end of the test paper to the other end under the pull of the capillary force formed by the paper fiber. In this process, N protein will go through three hurdles.

        Remarks: the first level: gold labeled antibody (gold labeled 2019 ncov antibody); The second level: T-line antibody (2019 ncov antibody); The third level: c-line antibody (“gold label 2019 ncov antibody” secondary antibody)

Detection of coronavirus antigen Kit

 Detection of coronavirus antigen Kit

1. Test effect display

2、Antigener_Detector

    The antigener detector completes the detection by two methods. Thereby improving the recall rate of positive samples.        First, target detection was performed using the ppyoloe-s model trained on the data set (Coronavirus antigen detection reagent data set). Then the traditional visual algorithm is used to post process the detected subject. Finally, the two results are used to judge.3. Training of detection model
3.1 introduction to detection model