Over 36 million people worldwide have been infected with the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) since the virus emerged in Wuhan, China, in late December 2019. The SARS-CoV-2 virus that causes COVID-19 disease is known to survive on skin and inanimate objects and can be easily transmitted from person to person.
Japanese researchers have now studied the survival possibilities of the flu virus and the SARS-CoV-2 on human skin. Their study titled, "Survival of SARS-CoV-2 and influenza virus on the human skin: Importance of hand hygiene in COVID-19," is published in the latest issue of the journal Clinical Infectious Diseases.
Transmission electron micrograph of a SARS-CoV-2 virus particle, isolated from a patient. Image captured and color-enhanced at the NIAID Integrated Research Facility (IRF) in Fort Detrick, Maryland. Credit: NIAID
The research was an attempt by researchers from the Kyoto Prefectural University of Medicine in Japan to study the stability of the SARS-CoV-2 on human skin.
Since live SARS-CoV-2 can not be used, the team had first to create a model that would allow them to experiment with the application of pathogens on human skin.
Hand washing and hand hygiene
Several studies have shown that one of the best ways to prevent transmission of highly infectious viruses such as the novel coronavirus and the flu virus is repeated washing of the hands with soap and water for at least 20 seconds and sanitizing the hands with alcohol-based sanitizers with at least 70 percent alcohol content.
The authors wrote that studies have shown that the SARS-CoV and Middle East respiratory syndrome coronavirus (MERS-CoV) have higher stability compared to influenza A virus (IAV).
Models for experiment
It is unethical and dangerous for human subjects' skin to be exposed to highly pathogenic SARS CoV-2 or IAV (PR8; A/Puerto Rico/8/1934; H1N1). Thus skin samples need to be obtained via surgical procedures, which proved to be inadequate. Thus the team gathered forensic autopsy samples of human skin obtained from the Department of Forensic Medicine, Kyoto Prefectural University of Medicine, for their experiments.
The team explained that human skin, especially the epidermis deteriorates slowly after death compared to other organs and can be used for grafting even 24 hours after death. They collected abdominal skin samples from deceased persons aged between 20 and 70 years. The post mortem duration was within 24 hours, and these skin samples were cut into rectangles that measured around 4 × 8 cm2.
The viruses and the experiment
The team prepared a mix of the SARS-CoV-2 and influenza A virus (IAV) with culture medium or upper respiratory mucus. This mixture was applied to the human skin surfaces. They then disinfected the surfaces with 80% (w/w) ethanol and checked if the viruses survived.
The team analyzed the stability of SARS-CoV-2 and compared it with that of IAV. IAV is known to be transmitted through droplets and contact transmission. Using this model, they analyzed the stability of the viruses on;
- the surface of stainless steel,
- the surface of borosilicate glass,
- the surface of polystyrene,
- the surface of human skin.
Next, they mixed the SARS-CoV-2 and IAV with mucus from the upper respiratory tract. They explained that these viruses tend to be transmitted via infectious body fluids (mucus).
In their experiment, they looked at the effectiveness of 80 percent (w/w) ethanol in the disinfection of human skin, which had been exposed to SARS-CoV-2 or IAV.
Results and findings
The team first validated their experimental model using the IAV samples on the skin. They also assessed the stability of the SARS-CoV-2 and IAV mixed in a cell culture medium.
This was evaluated on various surfaces, and it was seen that the survival time of SARS-CoV-2 was approximately 8-fold the survival time of IAV on these surfaces, and the former was found to have higher stability.
When tested on human skin, however, the viruses were rapidly inactivated compared to stainless steel, borosilicate glass, and polystyrene surfaces. SARS-CoV-2 was more stable on human skin surfaces compared to IAV.
Survival times were an average 9.04 hours compared to 1.82 hours for SARS CoV-2 and IAV, respectively. The half-life times of the viruses were 3.53 hours and 0.80 hours for SARS CoV-2 and IAV, respectively.
When mixed with mucus, the stability was analyzed and the team noted:
- IAV was more rapidly inactivated in mucus on inanimate surfaces compared to when it was in cell culture medium (Dulbecco's modified Eagle's medium or DMEM)
- Stability of SARS-CoV-2 in mucus and cell medium (DMEM) was similar
- Survival and half-life times of SARS-CoV-2 in mucus was significantly longer than IAV on human skin
- Survival times were an average 11.09 hours compared to 1.69 hours for SARS CoV-2 and IAV, respectively, in mucus on human skin.
- Half-life times were an average 4.16 hours compared to 0.77 hours for SARS CoV-2 and IAV, respectively in mucus on human skin.
- SARS-CoV-2 and IAV both in mucus and DMEM was completely inactivated on all human skin after 15 seconds of treatment with 80 percent (w/w) ethanol.
Conclusions and implications
This study shows that the SARS-CoV-2 could survive on human skin for up to 9 hours, and thus there is a risk of contact transmission.
The survival of the coronavirus on the skin is significantly longer than the flu virus making its spread a more significant public health problem.
The authors of the study wrote, "Proper hand hygiene is important to prevent the spread of SARS-CoV-2 infections." It takes only 15 seconds of 80 percent ethanol treatment to kill either virus on human skin, they found.
- Ryohei Hirose, Hiroshi Ikegaya, Yuji Naito, Naoto Watanabe, Takuma Yoshida, Risa Bandou, Tomo Daidoji, Yoshito Itoh, Takaaki Nakaya, Survival of SARS-CoV-2 and influenza virus on the human skin: Importance of hand hygiene in COVID-19, Clinical Infectious Diseases, , ciaa1517, https://doi.org/10.1093/cid/ciaa1517, https://academic.oup.com/cid/advance-article/doi/10.1093/cid/ciaa1517/5917611