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Los Angeles County’s novel coronavirus cases spiked to 1,216 Thursday as the nation’s most populous county stepped up its testing for the respiratory illness that has killed 21 people countywide.

The Los Angeles County Department of Public Health reported 421 new COVID-19 cases and nine coronavirus-related deaths in a news conference Thursday. One of the previously reported deaths is no longer being counted since the person is from another county, officials said.

“Reporting these deaths are the absolute worst part of our day at DPH, but it can’t compare to the profound loss that is experienced by the family and friends of people who have passed,” the department’s director Dr. Barbara Ferrer said.

The cases reported Thursday are more than three times the 138 cases reported the day before.

Ferrer said the surge in new cases mainly comes from a “huge” increase in testing capacity and from labs catching up on a backlog of tests.

About 4,000 people were tested for the coronavirus or received the results of their tests on Wednesday alone, according to Ferrer.

But even as the spike is largely attributed to better testing, health experts believe the virus is still spreading across the county.

Ferrer said that if 1,000 COVID-19 patients infect two other people each, over a million people in L.A. County could be infected with the coronavirus within a few weeks.

And since about 21% of all COVID-19 patients in the county have needed hospitalization, if that percentage of the hypothetical new patients need hospital care, local medical centers would be faced with a flood of over 200,000 new patients, Ferrer said.

“If we get the numbers down and each person does not infect two other people, that’s our chance and that’s our hope,” she said.

L.A. officials announced on Monday that the county bought 20,000 new COVID-19 test kits from a South Korean company, which has also committed to provide L.A. with 100,000 tests every week after the first batch is rolled out to first responders and health care workers. In the meantime, leaders vowed to continue forming partnerships and contracting more companies to secure more testing.

Ferrer said that though the county’s capacity to test people is getting better, supplies remain limited and only symptomatic people should be tested.

Out of the 9,400 people tested for the virus in L.A. County as of Wednesday, 10% of them have tested positive, according to Ferrer.

Officials didn’t provide additional details on the deaths announced Thursday as some families had not yet been notified.

The county’s coronavirus cases include 41 in Long Beach and nine in Pasadena, which both have their own public health agencies.

As more cases are reported throughout the state, officials have urged residents to stay home and keep at least 6 feet away from strangers when outside, explaining that it’s the best way to curb the spread of the new respiratory illness in the absence of a vaccine.

COVID-19 cases in the state topped 3,000 Thursday, with California’s top medical adviser reporting that cases have continued to double every three to four days, the Los Angeles Times reported.

With the pandemic threatening to strain the state’s hospitals as emergency rooms and intensive care units brace for a flood of patients, the U.S. Navy hospital ship Mercy is on its way to the Port of Los Angeles and is expected to dock Friday with an additional 1,000 hospital beds to help local hospitals.

Supervisor Kathryn Barger told residents they can serve their community by donating blood, giving to the homeless, supporting local businesses and checking in on neighbors who may need food.