CDC on Wednesday updated its definition of what it means to have "close contact" with a person infected with the novel coronavirus, and observers say the change could have broad implications for workplaces, schools, contact tracing, testing, and more.

US coronavirus epidemic is 'approaching a critical phase' amid surge in new cases, CDC director says

CDC's update comes as U.S. officials as of Thursday morning reported a total of 8,378,700 cases of the novel coronavirus since the country's epidemic began—up from about 8,316,000 cases reported as of Wednesday morning.

According to the New York Times, the United States' average daily number of newly reported coronavirus cases over the past week was 60,572—which is up by 32% when compared with the average from two weeks ago. On Wednesday, U.S. officials reported about 62,751 new cases of the virus, the Times reports.

During a briefing on Wednesday, CDC Director Robert Redfield said the United States is "approaching a critical phase" in the country's coronavirus epidemic. CDC officials said they're seeing newly reported coronavirus cases spike in nearly 75% of the United States—with the Midwest experiencing the largest surges.

"We are seeing a distressing trend here in the United States of Covid-19 cases increasing," Jay Butler, CDC's deputy director of infectious diseases, said.

Data from the Times shows that the rates of newly reported coronavirus cases are "staying high" in Guam and 32 states that have had a daily average of at least 15 newly reported cases per 100,000 people over the past week. Those states are Alabama, Alaska, Arkansas, Colorado, Idaho, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Michigan, Minnesota, Mississippi, Missouri, Montana, Nebraska, Nevada, New Mexico, North Carolina, North Dakota, Ohio, Oklahoma, Rhode Island, South Carolina, South Dakota, Tennessee, Texas, Utah, West Virginia, Wisconsin, and Wyoming.

Ten states that have had comparatively low case rates are now seeing those rates "going up," according to the Times. Those states are Arizona, Connecticut, Florida, Georgia, Massachusetts, New Hampshire, New Jersey, Pennsylvania, Virginia, and Washington.

In the 11 remaining U.S. states and territories, rates of newly reported coronavirus cases are "staying low," according to the Times' analysis.

CDC officials said they believe part of the reason why cases are increasing is that colder weather is driving more people indoors, where transmission of the virus is more likely. Officials also said some Americans may be fatigued with practicing measures intended to curb the coronavirus's spread, such as wearing masks and social distancing.

"I recognize that we are all getting tired of the impact that Covid-19 has had on our lives," Butler said. "We get tired of wearing masks, but it continues to be as important as it's ever been, and I would say it's more important than ever as we move into the fall season" and people are more likely to gather to celebrate upcoming holidays.

U.S. officials as of Thursday morning also reported a total of 222,157 deaths linked to the coronavirus since the country's epidemic began—up from about 220,987 deaths reported as of Wednesday morning. According to the Times, officials reported at least 1,170 new deaths linked to the virus on Wednesday.

CDC updates definition of a 'close contact' for coronavirus exposure

As newly reported coronavirus cases continue to climb throughout the United States, CDC on Wednesday updated its definition of what it means to have "close contact" with a person infected with the virus, citing new evidence that showed the pathogen can be transmitted during brief interactions.

Previously, CDC defined a "close contact" as a person who had spent more than 15 consecutive minutes within six feet of an infected individual. But under its newly updated definition, CDC now defines a "close contact" as a person who has spent a cumulative 15 minutes or more within six feet of an infected individuals across a 24-hour period—meaning those 15 minutes of exposure did not have to occur consecutively at one time, but could occur cumulatively throughout different, shorter points of contact over the course of a day.

CDC updated definition based on a case study the agency published on Wednesday, which describes how a 20-year-old correctional officer in Vermont appears to have contracted the novel coronavirus during "multiple brief encounters" with six incarcerated people who were infected.

After the correctional officer tested positive for the virus in August, officials from CDC, Vermont's Department of Health, and Vermont's Department of Corrections reviewed surveillance footage to examine the officer's interactions with the six incarcerated people with Covid-19. The officials found the officer had never spent 15 consecutive minutes within six feet of any of the infected people, but he had been within six feet of them at least 22 times during one of his eight-hour shifts, which amounted to at least 17 cumulative minutes of exposure. According to the case study, the incarcerated people who were infected with the virus wore face masks most of the time during their interactions with the officer—and the officer had always worn a microfiber cloth mask, gown, and eye protection during the encounters.

Officials said the officer had no known contact with any other people infected with the coronavirus when he became infected, and coronavirus cases in his county and the rest of the correctional facility had been low at the time. As a result, the officials concluded that the officer likely contracted the virus through his brief encounters with the incarcerated people who were infected.

Definition change could affect contact tracing, testing, and more

Researchers in the case study noted that "15 minutes of close exposure is used as an operational definition for contact tracing investigations in many settings." As a result, their findings—and CDC's corresponding definition change—could have implications for contact tracing and testing efforts, as well as effects on decisions relating to quarantining and in-person work or school.

For example, William Schaffner, an infectious disease expert at Vanderbilt University, explained that CDC's update could result in health departments conducting contract tracing in cases where exposure to the novel coronavirus previously might have been considered too brief for such efforts.

Further, as the Associated Press reports, CDC recommends that anyone who has had close contact with a person infected with the virus should quarantine for two weeks—and the number of people who are considered to have close contact with infected individuals could increase under CDC's new definition.

Overall, CDC officials said the new case study and definition highlight the importance of wearing masks to help mitigate the coronavirus's spread and that CDC's guidance will continue to change as scientists learn more about the virus.

"As we get more data and understand this [coronavirus] we're going to continue to incorporate that in our recommendations," Redfield said (King, FierceHealthcare, 10/21; Hellmann, The Hill, 10/21; Joseph, STAT News, 10/21; Owens, "Vitals," Axios, 10/22; Stobbe, Associated Press, 10/21; Ehley, Politico, 10/21; Pringle et al., CDC Morbidity and Mortality Weekly Report, 10/21; New York Times, 10/22).