According to CNN, a news release from the Los Angeles Department of Public Health advised doctors not to test patients with mild respiratory symptoms unless "a diagnostic result will change clinical management or inform public health response".
Why it matters: The fatality rate for COVID-19 in the U.S.is highest among those over 85, the CDC found in a report issued last week - and no deaths among people under 19 years of age were reported in the country as of March 18.
"Each loss we experience in LA County is tragic, and we are sending our heartfelt condolences to the families and loved ones who've had to endure this tragedy", Los Angeles County Public Health Director Barbara Ferrer said in a statement.
The death was one of four reported in the county on Tuesday, with a total of 11 reported since the pandemic began.
Public health officials in California's Los Angeles county announced what is believed to be the first USA death of a patient under 18 years old from the COVID-19 coronavirus on Tuesday.
Los Angeles County health officials on March 21 issued an "enhanced" health officer order prohibiting all gatherings and events, and that non-essential services should remain closed.
Less than three percent of hospitalisations from coronavirus were due to that age group. No other information is so far known about their identity.
Ferrer also confirmed there were 128 new cases, bring the county's tally to 662.
As of Tuesday, at least 53,660 cases of COVID-19 have been reported in the United States, and 703 people have died, according to a tracker maintained by researchers at Johns Hopkins University.