Guidelines from the Centers for Disease Control and Prevention making the rounds this week on the internet are clarifying what we know about the transmission of the coronavirus.
The virus does not spread easily via contaminated surfaces, according to the C.D.C. For those who were worried about wiping down grocery bags or disinfecting mailed packages, the news headlines highlighting this guidance in recent days might have brought some relief.
But this information is not new: The C.D.C. has been using similar language for months. If anything, the headlines have pulled into sharper focus what we already know about the virus.
The coronavirus is thought to spread mainly from one person to another, typically through droplets when an infected person sneezes, coughs or talks at close range — even if that person is not showing symptoms.
“The virus that causes Covid-19 is spreading very easily and sustainably between people,” the C.D.C. says on its website. “Information from the ongoing Covid-19 pandemic suggest that this virus is spreading more efficiently than influenza, but not as efficiently as measles, which is highly contagious.”
The website also says that people can become infected by “touching a surface or object that has the virus on it and then touching their own mouth, nose, or possibly their eyes.” But those are “not thought to be the main way the virus spreads.”
The format of the C.D.C. website was slightly altered this month, but the language about surfaces remained the same. It appears to have been placed under a new subheading — “The virus does not spread easily in other ways” —on May 11, and more information about the difficulty of catching the virus from animals was added.
Kristen Nordlund, a spokeswoman for the agency, told The Washington Post that the revisions followed an internal review and were the product of “usability testing.”
“Our transmission language has not changed,” Ms. Nordlund said. “Covid-19 spreads mainly through close contact from person to person.”
Experts at the C.D.C. and elsewhere are still learning about the new coronavirus.
There are questions about how the density of virus particles could affect transmission rates. Researchers don’t yet know whether all speech, cough and sneeze droplets carrying the particles are equally infectious, or if a specific amount of virus needs to be transmitted for a person to get sick by breathing it in. A study last week found that talking alone can launch thousands of droplets into the air, and that they can remain suspended for eight to 14 minutes.
It seems that the virus spreads most easily when people are in close contact with one another — in a conversation, for example — or gathered in poorly ventilated spaces, said Linsey Marr, an aerosol scientist at Virginia Tech.
She said that in order for a person to catch the virus from a surface, it would seem that a few things would have to happen. First, the virus would have to be transmitted to the surface in large enough amounts. Then, it would have to survive on that surface until it was touched by someone else. And even if it was eventually transferred to, say, a person’s finger, it would then have to survive on the skin until that person happened to touch an eye or mouth.
“There’s just a lot more conditions that have to be met for transmission to happen via touching these objects,” Dr. Marr said.
A lot of what we know about how long the virus lives on surfaces comes from a study published in The New England Journal of Medicine in March. The study found that the virus can survive, under ideal conditions, up to three days on hard metal surfaces and plastic and up to 24 hours on cardboard.
And since catching the coronavirus from a contaminated surface is still considered a possibility, people who prefer to wipe down bags, boxes or park benches can still do so. The C.D.C. recommends washing your hands often and regularly cleaning or disinfecting frequently touched surfaces.