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

U.S. health officials Wednesday redefined what counts as close contact with someone who hasCOVID-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 sixfeet or twometres of someone who tested positive for coronavirus. On Wednesday, the CDC changed thatto 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.

Italso 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 withcoronavirusin 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 maskson, the report said.

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

Dr. Anne Huang, aformer Saskatchewan deputy medical health officer, said the study offers high-quality data to show current understanding of physical distancing isn'tadequate.

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

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