1 week, 6 days ago

Although there is no consensus on the survival time of the new coronavirus in vitro, the accuracy of the number is not the most important. The key is how we use it to guide daily protection. 

 
 
 the new coronavirus is not easy to survive in the porous material containing fiber

The epidemic hasn't completely passed. Many people are worried about the possible poison on the surface of objects when they go out. When they open the door, they only push with their elbows. Whether they want to grab the handrail on the subway or not has to fight inside. There are also people who are careless, and everything is as usual. What's the risk of new coronavirus infecting through goods? 

A new study shows that the virus can survive for 4 hours on the surface of copper, 2 days on the surface of stainless steel and 3 days on the surface of plastic. What does that mean? 


 
 different surfaces have different virus survivability

The confirmed routes of transmission of the new coronavirus include 
 droplet transmission 
 (inhalation of droplets emitted by the infected person during sneezing, coughing and speaking), 
 contact transmission 
 (contact with the surface of the object contaminated by droplets of the infected person, and then touch the mucous membrane such as the eyes, nose and mouth of the infected person) and 
 aerosol transmission 
 (the virus is mixed in the micro tissue invisible to the naked eye Small droplets, stay in the air, and then be inhaled). 

Avoiding close contact with others and wearing masks correctly can effectively prevent the spread of droplets. But experts caution against exposure and aerosol transmission. 

Aerosols with a diameter of less than 10 microns can be suspended in the air for more than half an hour, and can also fall down on the surface of the object, resulting in the continuation of infectivity. 

 
 
 aerosols, droplets and contaminated objects | coreharow. WordPress. Com 
 
 
 how strong this continuation is is related to the ability of the virus to maintain activity on the surface of the object. 

A new study, published in the New England Journal of medicine, shows that viruses live for different times on different surfaces. 

The survival of the new coronavirus was simulated when the infected person coughed (aerosol), touched different objects (copper, cardboard, stainless steel and plastic). 

As a result, new coronavirus can be detected in Aerosol Observation for up to 3 hours. 


 these viruses can only survive for 4 hours on copper surface, 24 hours on cardboard, 2 days on stainless steel surface and 3 days on plastic surface. 


 
 
 the survival time of new coronavirus on different surfaces (copper handle, carton, stainless steel door, plastic seat) is not the same | the author's drawing 
 
 
 this is not surprising:

Copper is a natural metal with antimicrobial properties. When copper ion reacts with water in the air, it can produce free radicals which can destroy the outer shell and inner nucleic acid of the virus. 

Because of its loose texture, the fiber contained in the cardboard can absorb the water in the environment, leading to the drying of the virus shell, which may be one of the reasons for the short survival time of the virus. 

On hard, smooth, non porous surfaces such as plastics and stainless steel, viruses retain moisture more easily, thus maintaining structure and activity longer. 

 
 
 porous materials with fibers are more likely to dry up the virus surface. 
 
 
 
 the actual infectivity, and the virus concentration 
 


However, it is not the virus that can survive and spread. The actual infectivity depends on the concentration of the virus. 

In short, 
 on the surface of inanimate objects, the number of live viruses drops faster. 


On the hardboard, the median time to reduce the number of live viruses by half is less than 4 hours (that is, the virus concentration will be halved if the average time is less than 4 hours), while on the stainless steel and plastic surfaces, it is 5.6 and 6.8 hours respectively. 

This means that under normal circumstances, the amount of virus on express packages will not be too much, and we do not have to be on the subway. 

However, we don't know whether the courier has coughed or sneezed without cover when handling the package, nor how long ago the infected people touched various handles and elevator buttons. Therefore, 
 washing hands frequently and disinfecting the articles contacting too many people are very important protective measures. 


In addition, it was found that the number of live viruses in aerosols decreased very slowly in 
 closed environment. 


The higher the virus concentration, the higher the risk of infection. As for the specific number, there is no clear conclusion at present. Therefore, experts call for good indoor ventilation, 
 air circulation can reduce the virus concentration of aerosols and reduce the risk of infection. 



 the study also compared the difference between the new coronavirus and SARS virus 
. 

The results showed that the two viruses had similar stability on the surface of other objects except for the longer survival time of the new coronavirus (24 hours, while the longest survival time of SARS virus was 8 hours). There may be another reason for the difference between the two. 

In addition, at different stages of infection, the ability of patients to infect others is not the same. In the early stage of the disease, the viral load of the upper respiratory tract in the patients with new coronavirus was higher than that in the patients with new coronavirus. However, the viral load of SARS patients' respiratory tract is moderate, and the peak of viral load is only 10 days after symptoms appear. 

This means that the SARS virus has a stronger transmission ability several days after the onset of the disease, while the new coronavirus has the potential of early transmission and is more cunning. 

The research on 
 
 is not comprehensive, but the existing countermeasures are worth adhering to

In general, the results support the rationality of new coronavirus aerosol transmission and pollutant contact transmission, and confirm the existing public health control measures. But 
 there are still many materials that can not be verified one by one, such as clothing, rubber, glass, wood, etc. These are all the materials that we come into contact with every day. 

In addition, due to the different experimental conditions, there is no unified view on how long the new coronavirus can survive outside the human body. Temperature, humidity and sunshine may affect the life of virus. 

For example, previous studies have shown that the virus can survive for nine days on a metal handle, and even 28 days in a cold environment. 

In fact, the accuracy of numbers is not the most important. The key is how we use it to guide our daily protection. 

All the data indicate that the survival time of the new coronavirus on the smooth and porous surface is longer, and the corresponding factors that can destroy its structural stability can lead to its inactivation 
. 

Such as high temperature treatment above 56 ℃ for 30 minutes, ultraviolet irradiation for 1 hour, etc. However, these measures have requirements for both intensity and time. It does not mean that turning on the heating air conditioner and basking in the sun for a few minutes can kill the virus. 

In contrast, the impact of chemicals is more direct, such as washing hands with soap and water, 0.5% hydrogen peroxide or 62-71% alcohol, which can make the virus inactivated within one minute. 

Because the most important way of virus infection is to contact with the mucous membrane of eyes, mouth and nose, 
 to avoid pollutants touching the five senses, and to do a good job in hand and public goods cleaning is to take constant and ever-changing countermeasures 
. Including:

 
 wash hands in public places (especially toilets) for 20-30 seconds. Soap is recommended, hand sanitizer is only for standby

Avoid touching your facial features with your hands after touching objects in public places (elevator buttons, ATMs)

Disinfect the surfaces of objects that are often touched, such as mobile phones, keyboards, door handles, etc

When you go home, don't put your coat, trousers or shoes at will

Window ventilation

 
 
 
 some cleaning strategies for aerosol and contact transmission (hand washing, avoiding eye and nose touching, disinfection and ventilation of frequently contacted items)| At present, we have achieved the stage victory, but the epidemic is still continuing. We should "despise strategically and attach importance to tactically": we don't have to be careless about public goods, and we can't think that wearing a mask is good for everything. In order to protect ourselves and others' health, we must add the protection consciousness of aerosol and contact propagation into our daily habits. 

Reference:

van Doremalen N, Bushmaker T, Morris DH, et al. Aerosol and SurfaceStability of SARS-CoV-2 as Compared with SARS-CoV-1 [published online ahead of print, 2020 Mar 17].
N Engl J Med
.2020;10.1056/NEJMc2004973.

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