According to Newsom's tweet, the family learned late Friday evening that they had come into contact with a California Highway Patrol officer who had tested positive for COVID-19. The officer provides security for the Newsom family.
Newsom and his wife, Jennifer, did not have contact with that officer, but three of the four children did. Newsom's children range in age from 4 to 11.
Newsom says he and his family tested negative for the virus on Sunday and are following "local guidance" by quarantining for 14 days.
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On Friday, a spokesman for the governor said one of his children may have been exposed to COVID-19 at school.
The child began a 14-day quarantine "from the date of exposure" after the family was told a classmate at the private school had tested positive for COVID-19, a spokesperson for the governor, Nathan Click, said in an emailed statement.
The school where Newsom's child may have been exposed will stop in-person learning and move to remote learning after the Thanksgiving break through the second week of December, in part because of the higher infection risks associated with holiday activities, according to an email Politico said it had obtained.
Late Friday evening, @JenSiebelNewsom and I learned that 3 of our children had been exposed to an officer from the California Highway Patrol who had tested positive for COVID-19.— Gavin Newsom (@GavinNewsom) November 23, 2020
Jen and I had no direct interaction with the officer and wish them a speedy recovery.— Gavin Newsom (@GavinNewsom) November 23, 2020
Thankfully, the entire family tested negative today. However, consistent with local guidance, we will be quarantining for 14 days.
The family is quarantining at their home in Sacramento County. They will be tested regularly, spokesman Jesse Melgar said in an emailed statement to the Associated Press.
Newsom said last month that his children had returned to their private school in Sacramento, sparking criticism even as millions of public schoolchildren continue to study online or through other distance learning measures because of COVID-19 concerns.
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The governor also drew fire this week for apparently flouting the very social distancing rules that he has urged Californians to follow assiduously to curb a spiking COVID-19 infection rate.
Newsom said this week he made a "bad mistake" by attending a friend's birthday dinner on Nov. 6 at the ritzy French Laundry restaurant in Napa County. He apologized and described the dinner as outdoors. But photos obtained by the Fox 11 TV station in Los Angeles show Newsom and his wife, Jennifer Siebel Newsom, sitting maskless around a crowded table of 12 - including several lobbyists - inside a room that was enclosed on three sides.
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The Associated Press contributed to this report.