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In recent days, the progress of the global epidemic has made Singularity Cake gasp: 654.38+million cases were added in four days abroad, and the United States added more than 1 10,000 cases in a single day. As many countries approached the eve of the outbreak, there were more and more imported cases.

It is estimated that everyone has a big question mark like a cake of singularity: How did COVID-19 spread so fast, many times faster than SARS before 17?

A recent study published in the journal Infectious Diseases in The Lancet may give some answers: The research team of the University of Hong Kong analyzed 23 patients and found that the viral load in patients' saliva peaked in the first week when they developed COVID-19 symptoms such as fever and cough!

I hope that the comrades returning from overseas will take care of themselves and benefit others.

This characteristic of COVID-19 is very different from SARS and Middle East Respiratory Syndrome, and it is more similar to seasonal influenza, which also means that COVID-19 patients are highly contagious at the initial stage of the disease and when the symptoms are mild.

The analysis also showed that about 1/3 patients could detect COVID-19 RNA in saliva for more than 20 days, even after clinical rehabilitation, but these patients were not necessarily worse. Therefore, it may be debatable to take continuous negative nucleic acid test as the discharge standard.

Based on these two findings, the research team called for stricter prevention and control measures for COVID-19 patients, so as to avoid more human-to-human transmission. At the same time, in the prevention and control work, this method of taking saliva for virus detection can be used to reduce the discomfort of nose swab and throat swab inspection.

How contagious COVID-19 patients are and how long the infection period is has always been one of the focuses in this epidemic. Not long ago, the preprint analysis released by the team of the Eighth People's Hospital of Guangzhou and the University of Hong Kong showed that 44% of people in COVID-19 spread from person to person, probably before the patient developed symptoms.

People who don't know that they are carrying poison, carnival with others, the result is

Although they are all coronaviruses, if COVID-19 really has this feature, it will be very different from SARS and MERS before. Both of them reached the peak of infectivity after 7 days or even 10.

Moreover, according to Singularity Cake, at present, most European and American countries still don't adopt the strategy of "taking all due" when the China epidemic broke out, but let a large number of mild patients be isolated at home. For example, in Portugal, where the number of cases exceeded 2,000 yesterday, only more than 200 patients were officially admitted.

If mild patients are highly contagious, the second or even third infection will be very unfavorable for epidemic prevention and control. To analyze this problem, it is necessary to start with the changing trend of respiratory virus load in patients with new coronary pneumonia and make a complete evaluation combined with the course of the patient.

This is also the strategy adopted by the team of the University of Hong Kong in this analysis. In order to increase patients' cooperation, the research team did not use nasal swabs and throat swabs for sampling, but asked patients to cough up saliva under the guidance of nurses before brushing their teeth and eating breakfast every morning. This sampling method has been proved to be effective.

According to the characteristics of patients, among the 23 patients included in this analysis, 65,438+00 were severe and 65,438+03 were mild. The overall age distribution, clinical symptoms, imaging and laboratory examination features are similar to the previous analysis, and the main antiviral treatment is lopinavir/ritonavir.

No viral RNA was detected in saliva of 3 of the 23 patients, while the median viral load in saliva of the other 20 patients was 5.2log 10 copies/ml. In the changing trend, the viral load will peak in the first week after the symptoms appear, and then gradually decrease, but there is no such changing trend in the detection of tracheal attracting primers in severe patients.

The blue dot is the result of saliva test, and the red dot is the primer test of endotracheal sputum aspiration in severe patients.

According to the characteristics of patients, the viral load of elderly patients is relatively high, but there is no significant difference between severe and chronic patients and mild patients.

2 1 among the cured patients, 7 patients were RNA positive in saliva for more than 20 days, and the longest patient was 25 days. However, this long-term detection of virus has no obvious correlation with the duration and severity of patients' clinical symptoms.

In addition to the viral load, the antibody of COVID-19 patients is another focus of this analysis. The detection of serum antibody in patients with 16 showed that the level of antibody against COVID-19 nucleoprotein and surface spinosin receptor binding domain began to rise after COVID-19's symptom 10.

The changing trends of IgG and IgM, NP antibody and RBD antibody are different.

How to interpret this series of findings?

First, the problem of viral load. The research team pointed out in the paper that since the trend of viral load in COVID-19 is similar to that of influenza, early antiviral treatment may be crucial to improve the prognosis. However, the value of lopinavir/ritonavir used in this analysis has been proved to be limited by domestic experiments.

For the prevention and control of epidemic situation in COVID-19, the high viral load and strong infectivity in the early stage definitely mean that prevention and control is more difficult. However, the saliva detection method proposed by the research team is indeed more acceptable to the subjects. After all, some time ago, some foreign students returned to China and refused to do throat swab testing.

Secondly, for a few patients whose saliva nucleic acid test continues to be positive, the research group believes that the key is to determine whether these patients are still "detoxifying". If the patient's clinical symptoms basically disappear, continuing hospitalization will indeed crowd out medical resources, but from the perspective of infectious disease prevention, it is obviously risky to discharge drug addicts.

The answer to this question needs more research to confirm, as does the antibody level. After all, from the data of this analysis, the change of patients' antibody level has little to do with clinical symptoms, but COVID-19 should be treated with caution because the antibody of SARS virus may cause acute lung injury.

It's not easy for everyone in an emergency. I hope the epidemic will pass soon.

For more information about The Lancet's sub-issue: To find another reason why COVID-19 is super contagious, please continue to pay attention to the column of deep space science and technology information, and deep space Bian Xiao will continue to update you with more science and technology news.

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