Covid-19 coronavirus: CDC redefines virus close contact to add brief encounters

An ambulance is parked at the University Medical Centre in Las Vegas. Spikes of the coronavirus are hitting spots around the United States. Photo / AP

United States health officials today redefined what counts as close contact with someone with Covid-19 to include briefer but repeated encounters.

For months, the Centres for Disease Control and Prevention said close contact meant spending a solid 15 minutes within 2m of someone who tested positive for coronavirus.

Today, the CDC changed it 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.

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.

It's also serves notice that the coronavirus can spread more easily than many people realise, he added.

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The definition change was triggered by a study of a 20-year-old Vermont correctional officer, who was diagnosed with a coronavirus infection 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 them on, the report said.

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

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

- AP