COVID-19 transmission can happen in just a few minutes over the course of a day, the Centers for Disease Control said Tuesday.
The federal health agency had previously said that people should get tested if they’ve been within six feet of a COVID-19-positive person for more than 15 minutes at one time. But after studying a small outbreak at a Vermont prison, they updated the guidance to say that transmission can occur if someone is around another person who has the virus for a total of 15 minutes over a 24-hour period — even if each exposure was just two or three minutes at a time.
"Cumulative exposures can be as hazardous as 15 sustained continuous minutes of exposure," Dr. William Schaffner, an infectious disease expert at Vanderbilt University Medical Center, told NBC News.
The CDC made this change on Tuesday, after releasing its case report on the Vermont prison. The report focused on an outbreak in late July, when six new prisoners arrived and were put in quarantine while awaiting results of their COVID-19 tests. None had any virus symptoms when they entered quarantine, but the next day, all six tested positive for COVID-19.
During their contact tracing, the Vermont Department of Health identified a correctional officer who had been in contact with the prisoners, but determined that he had only been exposed to them for a few minutes at a time and likely had not contracted COVID-19. Yet seven days later, the officer had lost his sense of taste and smell, had a runny nose, cough, shortness of breath and headaches — all signs that he had COVID-19.
He tested positive on Aug. 11, and health officials determined that the prisoners were the only COVID-19-positive people the officer had encountered. After looking back on surveillance tapes, they saw that the officer had only been within six feet of the prisoners for about a minute at a time, far less than the 15 minutes needed to meet the CDC’s definition of exposure.
But it turned out that during his 8-hour shift that day, the officer had been around the prisoners during those quick encounters for 17 minutes in total. And while he had always worn a mask, the prisoners at times did not. The findings pushed the CDC to update their guidance on COVID-19 exposure.
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The case "significantly adds to the scientific knowledge of the risk to contacts of those with COVID-19 and highlights again the importance of wearing face masks to prevent transmission," the CDC said in a statement.
Schaffner said it may be that one of the prisoners was a “superspreader” and led to the transmission in such a short amount of time because they were “shedding an awful lot of virus,” but the case shows that “the more time you spend” with a COVID-19-positive person, “the more likely you are to get infected.”
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