The county's public health director, Barbara Ferrer, said she's asked the federal Centers for Disease Control and Prevention to investigate the death of the teen from the Mojave Desert city of Lancaster.
While the child did test positive for the coronavirus, there were "extenuating circumstances that pointed to an alternative diagnosis as well," she said.
The death is no longer being counted among LA County's 13 total fatalities from the virus. The county has tallied 799 residents who have tested positive.
Ferrer announced the death of the youth during a briefing Tuesday.
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Lancsaster Mayor R. Rex Parris said later Tuesday that a 17-year-old boy had been hospitalized with respiratory problems and died from septic shock, a reaction to a widespread infection that can cause dangerously low blood pressure and organ failure.
Parris said the boy's father also has coronavirus and worked in a job where he had close contact with the public.
The mayor said the boy may have had long-term health problems in the past but was healthy recently. He said he doesn't doubt that the teen died from complications of COVID-19.
Gov. Gavin Newsom on Wednesday chided county officials for the backtrack. "We all have been reminded in this moment it's not just speed, it's accuracy that must be front and center," Newsom said.
A report last week by the CDC found no coronavirus deaths in the U.S. among people 19 and under. That age group accounted for less than 3% of all hospitalizations.
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