A new study could have implications for how the general public and health care workers try to avoid transmission of the virus.
The coronavirus can live for three days on some surfaces, like plastic and steel, new research suggests. Experts say the risk of consumers getting infected from touching those materials is still low, although they offered additional warnings about how long the virus survives in air, which may have important implications for medical workers.
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The new study, published Tuesday in the New England Journal of Medicine, also suggests that the virus disintegrates over the course of a day on cardboard, lessening the worry among consumers that deliveries will spread the virus during this period of staying and working from home.
When the virus becomes suspended in droplets smaller than 5 micrometers — known as aerosols — it can stay suspended for about a half-hour, researchers said, before drifting down and settling on surfaces where it can linger for hours. The finding on aerosol in particular is inconsistent with the World Health Organization’s position that the virus is not transported by air.
The virus lives longest on plastic and steel, surviving for up to 72 hours. But the amount of viable virus decreases sharply over this time. It also does poorly on copper, surviving four hours. On cardboard, it survives up to 24 hours, which suggests packages that arrivein the mail should have only low levels of the virus— unless the delivery person has coughed or sneezed on it or has handled it with contaminated hands.
That’s true in general. Unless the people who handle any of these materials are sick, the actual risk of getting infected from any of these materials is low, experts said.
“Everything at the grocery store and restaurant takeout containers and bags could in theory have infectious virus on them,” said Dr. Linsey Marr, who was not a member of the research team but is an expert in the transmission of viruses by aerosol at Virginia Tech in Blacksburg. “We could go crazy discussing these ‘what-ifs’ because everyone is a potential source, so we have to focus on the biggest risks.”
If people are concerned about the risk, they could wipe down packages with disinfectant wipes and wash their hands, she said.
It is unclear why cardboard should be a less hospitable environment for the virus than plastic or steel, but it may be explained by the absorbency or fibrous quality of the packaging compared with the other surfaces.
That the virus can survive and stay infectious in aerosols is also important for health care workers.
For weeks experts have maintained that the virus is not airborne. But in fact, it can travel through the air and stay suspended for that period of about a half-hour.
The virus does not linger in the air at high enough levels to be a risk to most people who are not physically near an infected person. But the procedures health care workers use to care for infected patients are likely to generate aerosols.
“Once you get a patient in with severe pneumonia, the patients need to be intubated,” said Dr. Vincent Munster, a virologist at the National Institute of Allergy and Infectious Diseases who led the study. “All these handlings might generate aerosols and droplets.”
Health care workers might also collect those tiny droplets and larger ones on their protective gear when working with infected patients. They might resuspend these big and small droplets into the air when they take off this protective gear and become exposed to the virus then, Dr. Marr cautioned.
A study that is being reviewed by experts bears out this fear. And another study, published March 4 in JAMA, also indicates that the virus is transported by air. That study, based in Singapore, found the virus on a ventilator in the hospital room of an infected patient, where it could only have reached via the air.
Dr. Marr said the World Health Organization has so far referred to the virus as not airborne, but that health care workers should wear gear, including respirator masks, assuming that it is.