Federal health officials issued new guidance on Wednesday that greatly expands the pool of people considered at risk of contracting the novel coronavirus by changing the definition of who is a "close contact" of an infected individual.
The change by the Centers for Disease Control and Prevention is likely to have its biggest impact in schools, workplaces and other group settings where people are in contact with others for long periods of time. It also underscores the importance of mask-wearing to prevent spread of the virus.
The CDC had previously defined a "close contact" as someone who spent at least 15 consecutive minutes within six feet of a confirmed coronavirus case. The updated guidance, which health departments rely on to conduct contact tracing, now defines a close contact as someone who was within six feet of an infected individual for a total of 15 minutes or more over a 24-hour period, according to a CDC statement Wednesday.
The update comes as the United States is "unfortunately seeing a distressing trend, with cases increasing in nearly 75 percent of the country," Jay Butler, the CDC's deputy director for infectious diseases, said Wednesday at CDC headquarters in Atlanta, in the first news conference administration officials permitted in more than eight weeks. People may be tired of the advice, Butler said, but mask-wearing is more important than ever this fall and winter as Americans head indoors, where transmission risks are greater.
The guidance about transmission of the coronavirus, which causes covid-19, had been discussed by CDC scientists for several weeks, according to a CDC official who spoke on the condition of anonymity. Then came unsettling new evidence in a report published Wednesday. CDC and Vermont health officials discovered the virus was contracted by a 20-year-old prison employee who in an eight-hour shift had 22 interactions — for a total of over 17 minutes — with individuals who later tested positive for the virus.
"This article adds to the scientific knowledge of the risk to contacts of those with covid-19 and highlights again the importance of wearing face masks to prevent transmission," the CDC said.
As many as half of all people who have the virus don't show symptoms, "so it's critical to wear a mask because you could be carrying the virus and not know it," the CDC said. "While a mask provides some limited protection to the wearer, each additional person who wears a mask increases the individual protection for everyone. When more people wear masks, more people are protected."
Caitlin Rivers, an epidemiologist at the Johns Hopkins Center for Health Security, called the updated guidance an important change.
"It's easy to accumulate 15 minutes in small increments when you spend all day together — a few minutes at the water cooler, a few minutes in the elevator, and so on," Rivers said. "I expect this will result in many more people being identified as close contacts."
She added: "This change underscores the importance of vigilant social distancing — even multiple brief interactions can pose a risk."