The CDC is expanding its definition of 'close contact' when it comes to COVID-19. Here's why

U.S. health officials redefined what counts as close contact with someone who has COVID-19 to include briefer but repeated encounters. The change was triggered by a study of a correctional officer who caught the coronavirus after multiple brief encounters with prisoners who later tested positive.

Definition change triggered by study of guard who had brief but repeated encounters with infected prisoners

A medical worker administers a test at United Memorial Medical Center amid the global outbreak of COVID-19 in Houston, Texas, in June. U.S. health officials are redefining what it means to have close contact with someone who has COVID-19. (Callaghan O'Hare/Reuters)

U.S. health officials Wednesday redefined what counts as close contact with someone who has COVID-19 to include briefer but repeated encounters.

For months, the U.S. Centers for Disease Control and Prevention said close contact meant spending a solid 15 minutes within six feet or two metres of someone who tested positive for coronavirus. On Wednesday, the CDC changed that to a total of 15 minutes or more — so shorter but repeated contacts that add up to 15 minutes over a 24-hour period now count as close contact. 

The CDC advises anyone who has been in close contact with a COVID-19 patient to quarantine for two weeks.

The change may prompt health departments to do contact tracing in cases where an exposure might previously have been considered too brief, said Dr. William Schaffner, a Vanderbilt University infectious diseases expert.

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There is a lot of legwork involved in contact tracing that can slow it down, and the solution since the beginning should be to bring in more tracers in a concentrated manner, says respirologist Dr. Samir Gupta. 

It also serves notice that the coronavirus can spread more easily than many people realize, he said. 

The definition change was triggered by a study of a 20-year-old Vermont correctional officer, who was diagnosed with coronavirus in August.

The guard, who wore a mask and goggles, had multiple brief encounters with six transferred prisoners before test results showed they were positive.

At times, the prisoners wore masks, but there were encounters in cell doorways or in a recreational room where prisoners did not have masks on, the report said.

An investigation that reviewed video footage concluded the guard's brief interactions totalled 17 minutes during an eight-hour shift.

Dr. Anne Huang, a former Saskatchewan deputy medical health officer, said the study offers high-quality data to show current understanding of physical distancing isn't adequate.

"Our current public health contact tracing guidance in Canada isn't capturing all the transmission events," Huang said. She said she hopes federal and provincial public health officials will dig into this blind spot. 

In a statement, CDC officials said the case again highlights the importance of wearing masks to prevent transmission.

With files from CBC's Christine Birak


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