Coronavirus can stay infectious for days on surfaces

Risk of getting sick remains, but window shrinks as time passes

Scientists studying the novel coronavirus are quickly uncovering features that allow it to infect and sicken human beings. Every virus has a signature way of interacting with the world, and the new coronavirus, which is named SARSCoV-2 and causes the disease COVID-19, is well equipped to create a historic pandemic.

The coronavirus can be shed by people even before they develop symptoms. That presymptomatic transmission has helped it become a stealth contagion, spreading through communities before they know what hit them.

The coronavirus may take many days — up to 14 — before an infection flares into symptoms, and although most people recover without a serious illness, this is not a bug that comes and goes quickly. A serious case can last for weeks.

The virus lurks in the body even after people feel better. A new study in the Lancet, based on research in China, found that the median length of time the virus remains in the respiratory tract of a patient after symptoms begin is 20 days. Among patients who survived the disease, the virus continued to be shed for between eight and 37 days (the study did not reach any conclusions on whether and to what extent this persistence could lead to infections in other people).

This coronavirus can establish itself in the upper respiratory tract, said Vincent Munster, chief of the Virus Ecology Section of Rocky Mountain Laboratories, a facility in Montana that is part of the National Institute of Allergy and Infectious Diseases. That enables the virus to spread more easily through coughing and sneezing, and stands in contrast to another coronavirus that Munster’s laboratory has studied — MERS, which tends to infect cells in the lower respiratory tract, he said. Though more lethal than the new virus, MERS did not spread as easily and did not become a pandemic.

Munster and his colleagues have been studying the novel coronavirus under laboratory conditions to better understand its viability outside a host organism.

Those experiments found that at least some coronavirus can potentially remain viable — capable of infecting a person — for up to 24 hours on cardboard and up to three days on plastic and stainless steel.

When aerosolized into fine, floating particles, the virus remained viable for three hours. On a copper surface, it was four, the study found. The median length of viability for the virus on stainless steel was 13 hours, and 16 hours on polypropylene, a common type of plastic. The new paper from Munster and his team was posted on a preprint site, and it has not yet been published in a journal.

The researchers used a nebulizer to aerosolize the virus, but in a natural environment, the virus does not spread through aerosol particles. Certain hospital treatments can result in aerosolized virus, but the main way the virus has been spreading has been through droplets — like when someone sneezes or coughs. Such droplets can travel up to six feet.

As the coronavirus spreads, the simple act of touching a surface has become a delicate matter of risk analysis. The world is full of suspect surfaces. Is it safe to touch an ATM screen? Or the self-checkout at the grocery store? A door handle? A package that came in the mail?

The Centers for Disease Control and Prevention recommends that people take steps to clean and disinfect surfaces. But the durability of some coronavirus on a surface does not mean it remains just as infectious as the hours go by. Most virus particles degrade in a matter of minutes or hours outside a living host, and the quantity of infectious particles goes down exponentially over time.

Although it is theoretically possible for a person to become infected a day or two after someone has deposited virus particles on a surface, it is much less likely than in the first couple of hours after the sneeze, Munster said.

“The risk of becoming infected via these routes of transmission reduces over time,” Munster said. “That window of becoming infected is highest in the first 10 minutes, or one hour or two hours.”