The revised guidance now states, in headline-size type, “The virus spreads easily between people.” It also notes that the coronavirus, which causes the disease covid-19, “is spreading very easily and sustainably between people.”

The CDC made another key change to its website, clarifying what sources are not major risks. Under the new heading “The virus does not spread easily in other ways,” the agency explains that touching contaminated objects or surfaces does not appear to be a significant mode of transmission. The same is true for exposure to infected animals.

CDC spokeswoman Kristen Nordlund said Thursday that the revisions were the product of an internal review and “usability testing.”

“Our transmission language has not changed,” Nordlund said. “Covid-19 spreads mainly through close contact from person to person.”

The virus travels through the droplets a person produces when talking or coughing, the CDC website says. An individual does not need to feel sick or show symptoms to spread the submicroscopic virus. Close contact means within about six feet, the distance at which a sneeze flings heavy droplets.

Example after example have shown the microbe’s affinity for density. The virus has spread easily in nursing homes, prisons, cruise ships and meatpacking plants — places where many people are living or working in proximity. A recent CDC report described how a choir practice in Washington state in March became a super-spreader event when one sick person infected as many as 52 others.

“Direct contact with people has the highest likelihood of getting infected — being close to an infected person, rather than accepting a newspaper or a FedEx guy dropping off a box,” said virologist Vincent Munster, a researcher in the virus ecology section at Rocky Mountain Laboratories, a National Institute of Allergy and Infectious Diseases facility in Hamilton, Mont.

Munster and his colleagues showed in laboratory experiments that the virus remained potentially viable on cardboard for up to 24 hours and on plastic and metal surfaces for up to three days. But the virus typically degrades within hours when outside a host.

The change to the CDC website, without formal announcement or explanation, concerns Angela L. Rasmussen, a virologist at the Columbia University Mailman School of Public Health.

“A persistent problem in this pandemic has been lack of clear messaging from governmental leadership, and this is another unfortunate example of that trend,” Rasmussen said. “It could even have a detrimental effect on hand hygiene and encourage complacency about physical distancing or other measures.”

Right-wing social media exploited the website tweaks this week. Fox News commentator Sean Hannity promoted a “breaking” report about the change.

But the previous version of the website, archived May 1, includes the same statement about surfaces as the current version: “It may be possible that a person can get COVID-19 by touching a surface or object that has the virus on it and then touching their own mouth, nose, or possibly their eyes. This is not thought to be the main way the virus spreads, but we are still learning more about this virus.”

Rasmussen said the new CDC language will not alter her habits. “I wash my hands after handling packages and wipe down shared surfaces with household disinfectant,” she said. “In my opinion, that’s all that is necessary to reduce risk.”

And if people find comfort in “quarantining” their mail or wiping down plastic packaging with disinfectant, “there’s no harm in doing that,” Rasmussen said. “Just don’t wipe down food with disinfectant.”

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