How to Prepare for Coronavirus: Masks, Washing Hands, Masks and More

All eyes have been on the coronavirus since it crept up in Wuhan, China, in late 2019. Since then, the virus has sickened tens of thousands of people in more than three dozen countries, and its quick advance across Asia, the Middle East and Europe has raised fears that a pandemic could be on the horizon.

The World Health Organization has referred to the outbreak as an “epidemic” as opposed to a “pandemic.” But on Friday, it increased its assessment of the global risk of spread and the risk of impact of the coronavirus outbreak from “high” to “very high.”

According to the W.H.O., an epidemic is explained as a regional outbreak of an illness that spreads unexpectedly. The C.D.C. calls it “an increase, often sudden, in the number of cases of a disease above what is normally expected” in that area.

He added: “Does this virus have pandemic potential? Absolutely, it has. Are we there yet? From our assessment, not yet.”

So far, health officials have not witnessed “the uncontained global spread” of the virus, or evidence of “large-scale severe disease or death,” Dr. Tedros said.

“Groups in various organizations are working to define pandemic for this novel virus, which could take some time,” Mr. Jasarevic said.

So far, most of the observed cases, clusters and outbreaks have been traceable, meaning health officials have not seen evidence of widespread community transmission, he said. Some countries have even slowed or stopped transmission.

The terms epidemic and pandemic imply different approaches to a health crisis, said Dr. Jennifer Nuzzo, a senior scholar at the Johns Hopkins Center for Health Security.

An epidemic suggests that the virus may be geographically limited, and that intervention by health agencies could help stop the spread. For a pandemic, where many places could be affected, there may be consequences for how many people or how much money or supplies are available, she said.

When an outbreak covers the globe, international groups like the W.H.O. and the United Nations have to divide their resources across greater territory than during a regional epidemic, she said. That would make a pandemic far more difficult to manage.

The approach to dealing with the pathogen could also be different, Dr. Nuzzo said. If cases are everywhere, the authorities might stop trying to prevent it from entering a country and focus instead on trying to treat illness, slow the pathogen’s spread and protect vulnerable people.

“The situation could definitely get worse and that needs to be understood,” Dr. Rabinowitz said. “At the same time, it’s sufficiently concerning now that preparations should be underway to be ready for a worsening situation.”

Daniel Victor and Sui-Lee Wee contributed reporting.