The Spring Festival in 2020 is unforgettable. A pneumonia epidemic caused by novel coronavirus made many people anxious. How did this sudden outbreak of novel coronavirus happen and spread? How high is the mortality rate and transmission speed? How to reduce the possibility of infection?

Part number 1. affect

First, we need to know how the virus infects patients.

If a virus wants to enter a cell, it must have a corresponding receptor on the cell. For example, the common receptor of HIV is CD4 protein, which is usually on the surface of immune cells in blood, so HIV can spread through blood without worrying about air transmission.

This time, novel coronavirus's receptor, like SARS, is angiotensin converting enzyme 2 receptor (ACE2R). This means that in order to infect humans, the virus must first contact the cells with this receptor and complete the receptor binding. This receptor is mainly distributed in respiratory tract and small intestine, but it is also found in oral and nasal mucosa, but its distribution is relatively small.

The meaning of mucous membrane is to secrete mucus and keep it moist. There are a lot of mucosal cells in our lips, eyelids, nasal cavity and mouth. Theoretically, the infection begins when the virus touches your oral mucosa in some way and binds to the receptor.

In order to let you know what happened next, we made a simplified general process:

1. First, the envelope of coronavirus will fuse with the cell membrane, releasing a single RNA strand of viral genetic material. This RNA can be directly used as messenger RNA to fool ribosomes in cells and synthesize RNA replicase.

2.RNA replicase will generate RNA negative strand according to viral RNA, and this negative strand will continue to generate more viral RNA fragments and RNA positive strands with replicase, and these different RNA fragments will generate more viral protein structures different from ribosomes.

3. Finally, protein shell and RNA will combine to generate new coronavirus particles, which will be secreted out of cells through Golgi apparatus and infect new cells. Every infected cell will produce thousands of new virus particles, which will spread to trachea, bronchus and finally reach alveoli, causing pneumonia.

After the infection is completed, it is not difficult to spread. The saliva secreted by your three pairs of salivary glands will be mixed with the respiratory secretions of throat and other parts, so that the saliva wrapped with the virus will spread into the air with your sneezing and coughing and come into contact with other people's respiratory tract and mucous membranes. Droplets spread, mucosal infection, which is why coronavirus spreads so easily.

2065 438+09 2065 438+09 Patients in South China Seafood Market were hospitalized for 7 days due to fever, cough and dyspnea. Five days later, he never went to the seafood market again, and his wife was admitted to the hospital because of unexplained pneumonia.

On June 65438+1 October1day, 2020, the seafood market in South China was closed. 65438+14 1 person with newly diagnosed pneumonia on October 2nd. At this time, the citizens celebrating the Spring Festival did not know that a plague that might infect tens of thousands of people had begun.

The second part. connect

In this paper published in The Lancet on October 24th, 65438/kloc-0, we can know the details of the first diagnosed 4 1 patient.

As of 1 October 22nd1,4 1, 28 people were discharged and 6 people died. Fever and cough are the most common symptoms, from onset to dyspnea, with an average of 8 days. In the early stage of pneumonia, the signal of human-to-human transmission is already obvious. 4 1 people, 14 people have never been to South China seafood market.

Another paper of 65438124 October studies a Shenzhen family who traveled to Wuhan on 29 February, 65438.

The man who first showed symptoms began to have fever and diarrhea on the fourth day after arriving in Wuhan. Three days later, his wife, father-in-law and mother-in-law also began to have fever and cough. On October 5th, 65438/kloc-0, the whole family returned to Shenzhen. Four days later, my mother who had never been to Wuhan began to feel weak. Finally, in this family of seven, six people were diagnosed with COVID-19, including his son who had no obvious symptoms.

It is not difficult to spread coronavirus among close family members:

1. The first is sneezing. You will spit out more than 10000 droplets, up to 8 meters.

2. Then cough, 1000 ~ 2000 drops, up to 6 meters.

Finally, even if you speak calmly, you will produce about 500 drops per minute.

This is 0.34 seconds after you sneeze. Green is the trajectory of large water droplets exceeding 100 micron. Because they are heavy enough, they will land in 10 seconds. The red one is a fog cloud formed by small water droplets. They will evaporate quickly, become smaller in the air and become dry droplet cores. Protein, an epithelial cell, will be wrapped by coronavirus, floating in the air and touching other people's mucous membranes.

This paper of 65438+1October 30th further analyzed the data of the first batch of 425 confirmed patients in Wuhan.

In this table, the abscissa is the time from infection to onset, and the ordinate is the relative probability. It can be seen that most infected people will get sick within 7 days, and the average incubation period of the virus is 5.2 days. Now we know that among the 295 people diagnosed before 65438+1October 1 1 in 2020, only 45 people have been to South China seafood market, and there are 7 medical staff. But ten days later, people realized that they had to wear masks.

Recommended reading: Please keep the distance above 1 meter! 20 suggestions for safe travel must be read in advance.

The third part. mask

Since June 20, 2020, masks have become a scarce resource.

It seems that wearing a mask is a good idea. The multi-layer structure of the mask can effectively block large particles, and those nanoparticles will be adsorbed on the internal fibers due to electrostatic action.

Therefore, if the particle size is taken as the abscissa and the filtration efficiency as the ordinate, the filtration effect of these masks is actually a U-shaped curve. It can be seen that the most difficult to filter is actually particles with a diameter of about 0.3 microns. This is why most masks use the filtering ability of 0.3 micron sodium chloride as the test index, and N95 can filter more than 95% in the test.

The filtering effect of N95 is of course the best, but even the mask with the worst effect can achieve a protection rate of nearly 80% for particles above 10 micron, which is about one tenth of the diameter of our hair.

What is the size of the droplet core? According to this paper in 2007, 82% of the droplets produced by cough are concentrated in 0.74 ~ 2.438+02 microns.

Such common medical masks are enough for most droplet nuclei, and in a random experiment involving more than 2,800 influenza medical staff in the United States, there is not even a significant difference in influenza infection rate between N95 masks and medical masks. Therefore, don't worry about complicated mask types, brands and national standards.

More important than wearing N95: Have you washed your hands? Wash your hands, because you may have a live coronavirus on your hand. Take the SARS virus as an example. In this study by the Academy of Military Medical Sciences, they can live on glass, plastic and metal for at least 2 days. They stay everywhere with droplets, and your hand is likely to touch them. Then when you rub your eyes and pick your nose, the virus will come into contact with mucosal cells and complete the infection. So wash your hands for a long time.

The fourth part. courage

The last question is, how many more people will die?

This is the growth curve of the cumulative number of confirmed cases and deaths in China from 65438+ 10/0 to 65438+1 0/3/0. If you divide the total number of deaths by the total number of confirmed cases, you can get a mortality rate of about 2%. But this calculation method is not accurate.

According to the data of the first batch of 425 confirmed patients, we can know that the average incubation period of the virus is 5.2 days, 4.6 days from onset to treatment, 4.5 days from treatment to admission, and 3.5 days from admission to ICU. Assuming that it takes 3 days from ICU to death, the whole process is about 2 1 day. And if it can be diagnosed after 3 days, it will take about 8 days from diagnosis to death. Therefore, the patients who died on June 365438+1October 3 1 day were diagnosed on June 23.

If we divide the 124 people who died in these three days from October 29 to October 65,438+1October 3 1 into the 279 people diagnosed on October 23, the mortality rate is as high as 44.4%. However, due to the shortage of medical resources in Hubei Province, it is difficult to diagnose. Many elderly patients can only be diagnosed when they develop into severe diseases, and the mortality rate is definitely high. In contrast, the data of other regions in China except Hubei Province can better reflect the real situation.

65438+1October 29 ~ 65438+1October 3 1, three people died in other provinces of China, divided by 65438+1October 2/kloc-0 ~ 65438+/kloc-0. According to this fatality rate, the number of people infected in Hubei from June 2008 to October 2003 was 1 ~ 23, which should be 10700 instead of 279.

Of course, this is only a very rough calculation process, and the sample size is small, which is not necessarily so accurate. But with the improvement of future data, the results of mortality will become clearer and clearer. After the outbreak of the epidemic, many organizations also released their estimates of novel coronavirus's R0 value, most of which were between 2 and 3.

R0 (basic number of infections) refers to the average number of infected people who spread diseases without intervention. R0 in novel coronavirus is 2 ~ 3, which means that each infected person will transmit the virus to 2 ~ 3 people. This is also the reason why the early pneumonia began to break out.

However, with the strong intervention of the external environment, the average number of infected people will begin to decrease. For example, in 2003, the average number of people infected with SARS was 2.9 at first, then fluctuated between 2.0 and 3.5, and finally fell to 0.4 until it completely disappeared. For COVID-19, this curve is the same.

Recommended reading: Will feces spread to novel coronavirus? 10 Latest Notes

This plague makes us all nervous, but in fact, bad things happen every day. In the past few years, an average of 88,000 people died of respiratory diseases caused by influenza, 63,000 people died of traffic accidents and 38,000 people died of safety accidents. As long as we go out of the house, to the construction site, to the office and to the assembly line, the risk already exists. Of course, we should reduce the probability of misfortune as much as possible, but we praise courage because we humans always choose to do what we should do when we know the risks.

Finally, let's take a look at the protagonist of this pneumonia-this deformed ball with a diameter of about 0. 1 micron. Is it terrible? We already know its RNA sequence, its infection mechanism, transmission mechanism, clinical manifestations and death probability.