An investigation into how an employee contracted COVID-19 in the workplace has caused the CDC to change its definition of “close contact.” This impacts contact tracing and renews emphasis on workplace controls.
Previously, the CDC defined “close contact” as someone who spent at least 15 consecutive minutes within six feet of a confirmed coronavirus case.
The revised definition is, “Someone who was within six feet of an infected person for a cumulative total of 15 minutes or more over a 24-hour period.”
In other words, exposures should now be added together over a 24-hour period. For example, three five-minute exposures for a total of 15 minutes.
Why did the CDC make this change?
No contact was over 1 minute
A case study published in the CDC’s Morbidity and Mortality Weekly Report on Oct. 21 tells how a Vermont correctional officer is believed to have contracted the coronavirus.
The officer had brief contact with six incarcerated or detained people (IDP) who later all tested positive for the coronavirus. Days later, the officer tested positive.
The Vermont Department of Health and his employer conducted a contact tracing investigation using video surveillance footage.
The video showed the officer didn’t meet the old definition of close contact. He never spent 15 consecutive minutes within six feet of one of the IDPs.
He did have 22, brief (about one minute each) encounters that added up to about 17 minutes.
During most of the encounters, the IDPs wore cloth masks.
However, during several encounters in a cell doorway or in a recreation room, the IDPs didn’t wear masks.
The officer wore a microfiber cloth mask, gown and goggles during all encounters. He also wore gloves during most of the interactions.
The investigation notes there may have been additional interactions that weren’t found during the contact tracing investigation.
The officer had no other close contact exposures to anyone with the coronavirus.
One other corrections worker whose contact did meet the old definition also tested positive for the coronavirus.
Contact tracing impacts
Caitlin Rivers, an epidemiologist at the Johns Hopkins Center for Health Security, told The Washington Post the updated CDC guidance is an important change.
Noting that employees may interact with co-workers for “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” during contact tracing.
Rivers also said, “This change underscores the importance of vigilant social distancing.”