A small outbreak of Covid-19 in a Vermont prison has prompted a change in the Centers for Disease Control and Prevention's guidelines for what qualifies as close contact with an infected person — and illustrates the importance of wearing a mask.
The findings could affect how people gather as the weather grows cooler.
The updated guidance changes the definition of a "close contact" of a Covid-19 case to a person who has been within 6 feet of an infected person for a total of at least 15 minutes in a day. That includes multiple, but brief, encounters, one or two minutes at a time.
Previously, a close contact was defined as spending 15 consecutive minutes with a Covid-19 patient. Those changes were expected to be updated Wednesday on the CDC's website.
"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 in Nashville, Tennessee, said.
The CDC made the change after an investigation into a Covid-19 outbreak over the summer in a Vermont correctional facility. A report on the outbreak was published Wednesday in the CDC's Morbidity and Morality Weekly Report.
At the end of July, six new prisoners arrived at the facility and were placed in a quarantine unit while awaiting Covid-19 test results. None had any symptoms, but the next day, all six tested positive.
The Vermont Department of Health followed up with the corrections officer who'd been in contact with the prisoners, but determined the officer's interactions with the prisoners were so brief — about one minute at a time — that he was considered low risk. The experience did not meet the CDC's criteria at the time for "close contact" with a confirmed Covid-19 case, defined as closer than 6 feet for at least 15 minutes.
The officer continued working rather than going into quarantine.
About a week later, the officer started having symptoms of Covid-19: loss of smell and taste, muscle weakness, runny nose, cough, shortness of breath, headache, loss of appetite and an upset stomach. He tested positive. His only contact with confirmed cases, however, were the brief visits with the six prisoners.
Health officials went back and reviewed surveillance video of those encounters. The video showed that the officer had spent just about a minute at a time within 6 feet of prisoners who were later revealed to be presymptomatic.
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Over an eight-hour shift, those brief encounters added up to about 17 minutes total. The officer wore a mask, but the prisoners did not during some of the encounters.
The exposure was also traced to two other prison staff members who tested positive.
"This reinforces the importance of the fact that people with or without symptoms can be highly infectious," Schaffner said.
In a statement, the CDC said 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 more time you spend with someone" who is infected with Covid-19, Schaffner said, "the more likely you are to get infected. It may have been that one of these six prisoners was a superspreader shedding an awful lot of virus."
Because it's impossible to identify who might be carrying and shedding the virus without symptoms, Schaffner suggested looming holidays should be socially distant, with face coverings, or even virtual.
"We have to recognize that this will be this be the year of a Covid Thanksgiving," he said.
As many as half of all people who have Covid-19 do not show symptoms, according to the CDC.