The Centers for Disease Control and Prevention has changed the amount of time it takes for someone to be considered a "close contact" of a person with COVID-19.
Previous language defined a close contact as someone who spent at least 15 minutes within 6 feet of a person with a confirmed case.
The CDC now defines a close contact as someone who was within 6 feet of an infected person for a total of 15 minutes or more over a 24-hour period.
People considered close contacts are supposed to quarantine and get tested for the virus.
In a study published Wednesday, the CDC and Vermont health officials found that multiple short exposures to people confirmed to have COVID-19 led to transmission of the virus.
During the contact tracing investigation, it was discovered that the coronavirus was transmitted to a correctional facility employee who interacted with individuals later found to be positive for the coronavirus. The employee had 22 interactions totaling 17 minutes during an eight-hour shift.
Some of the employee's contacts with those later found to have COVID-19 occurred when the coronavirus-positive individuals were not wearing face masks. The CDC says the finding "highlights again the importance of wearing face masks to prevent transmission."
Epidemiologist Marc Lipsitch of the Harvard T.H. Chan School of Public Health told NPR in an email that the new definition "captures most of the instances where there would be transmission but doesn't vastly expand the number."
The change will "mostly impact workplaces, schools and other places where people spend all day together off and on," according to Caitlin Rivers, a senior scholar at the Johns Hopkins Bloomberg School of Public Health. She says it does have "the potential to significantly increase the number of people who are asked to quarantine."