This is the first federally funded study to look at the surface stability of the COVID-19 virus specifically. Previous to this, the World Health Organization had estimated the survival time on surfaces to be a "few hours to a few days" based on research on other coronaviruses.
While the COVID-19 is mostly spread among humans in an airborne form, such as from coughs and sneezes, the joint study by the NIH, Princeton University, UCLA and CDC researchers concludes that the likelihood of fomite transmission (from surfaces) is also significant. They found the COVID-19 virus can be detected for up to 3 days on plastic that has been in contact with the airborne virus.
The surfaces tested and the amount of time COVID-19 could be detected on each of them is listed here:
- Plastic (polypropylene), 72 hours
- Stainless steel (AISI 204), 48 hours
- Cardboard, 24 hours
- Copper, 4 hours
The researchers mention that the time shown above only reflects the time to get to a minimum level detected by their test equipment. Some trace of the virus would still be on the surface after that time. It is not known how much of the virus it takes to infect a person.
The above materials are common in a health care setting. The researchers were curious to study them after finding that 3,000 early cases of COVID-19 infection occurred while infected patients were in hospitals in China and the spread was often due to medical equipment that led to aerosol transmission (like nebulizers), inhaled by staff and patients and fomite transmission, picked up from surfaces.
The SARS epidemic was spread primarily in hospitals, according to this study. COVID-19, however, is now being primarily spread outside hospitals in communities.
The study compared the COVID-19 virus to the SARS virus and found the COVID-19 had a significantly longer life on cardboard but couldn’t explain why and cautioned against interpreting this result. The finding that copper destroys viruses confirms a 2015 University of Southampton study that found copper effective in helping to prevent the spread of respiratory viruses such as SARS and MERS. Glass, also common in a healthcare environment, was not tested.
The researchers caution that the aerosol used in their study was produced by a nebulizer, a machine that made an aerosol (<5 microns), finer than those than droplets produced by humans (>5 microns) when they cough and sneeze. The human-produced droplets are less likely to infect via aerosol transmission because they fall to the floor or a surface while the aerosol stays suspended in the air.
*The paper was available as a draft and still needs to undergo a peer review before it is accepted for publication.