Using artificial skin, researchers found that touching surfaces contaminated with SARS-CoV-2 can lead to transfer of virus to the skin.
The main mode of spreading of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is via airborne transmission via droplets from an infected person’s exhalation, cough, or sneeze. However, there is evidence that the virus can also spread when people come in contact with contaminated surfaces (known as ‘fomites’), with studies showing the virus can live for a few days on many surfaces.
This has led to a fear of touching objects used by many people. Public health guidelines suggest frequent hand washing and sanitization of communal objects. Another way to get around this problem is to coat objects with a coating that can kill viruses. But whether there is an actual transmission of the virus from the contaminated object to the skin is still unknown.
Researchers have now tested whether and how much virus transfers to the skin from objects and reported their results in a paper published on the medRxiv* preprint server.
Using artificial skin to test virus transfer
Because transmission to real human skin cannot be done because of biosafety reasons, the team used an artificial skin called Vitro-skin® because it is very similar in properties to natural human skin, and studies have found it to be a good human skin model.
The team made an artificial plastic finger and attached the artificial skin to it. They placed a droplet of a SARS-CoV-2 suspension on each solid surface they tested. They contacted the artificial skin for 10 s or 30 minutes with this contaminated solid, then removed the skin and placed it in a solution to remove the virus from it. The solution with the virus was tested to check its infectivity of Vero E6 cells. They calculated a transfer ratio, which is the ratio of virus infectivity on the finger to the infectivity of the original droplet.
They found that when a wet droplet with the virus is present on a surface, even a brief, light touch can transfer the virus to the finger. For glass, stainless steel, and Teflon surfaces, the transfer ratio was about 13-16%. Touching the surface after the droplet had dried transferred a lesser amount of virus, about 3-9%. Infected people can shed a large amount of virus, so the amount transferred can be quite significant.
Although this is lesser than that of a wet droplet, it is not less by biological standards. Effective disinfectants leave less than 0.1% of germs on the surface, reinforcing the importance of washing hands before touching our face.
However, the authors note that the virus could have been inactivated on the surface, and the transfer ratio includes inactivated viruses also, which could be significant.
The researchers hypothesized that a less wetting surface like Teflon might transfer more virus compared to a surface like glass where the water droplet spreads. But, they did not find a great difference between the transfer from both surfaces.
They did find that the porosity of the solid plays a role in virus transfer. There was less transfer of the virus when the droplet was placed on wettable materials such as tissue, wood, and porous glass, and the droplet could penetrate them. The droplet and the virus become trapped in the pores, and thus less is present on the surface for transfer.
They also found that the virus trapped in the paper once the droplet had dried can be reactivated and resuspended. This was not true for the other porous materials they tested.
Washing hands critical to prevent transmission
The transfer of virus tested here involved only a gentle pressure and a quick touch. Normal contact usually involves more time, different pressures, and different rubbing motions. Rubbing will likely lead to more virus transfer.
Infection requires another step of transfer of the virus from the skin to the respiratory system, again indicating the importance of handwashing. Although the infectious dose for a human is not known, for a Syrian hamster, only five virus particles are enough to cause infection.
Studies have shown the virus can survive for at least several hours on the skin. Thus, contaminated surfaces, especially non-porous surfaces, can transfer virus to the skin, even if the virus suspension has dried. Handwashing is thus an important part of preventing SARS-CoV-2 infection.
medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.