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Los Angeles County health officials confirmed 3,780 new cases of the coronavirus Saturday, the highest number of infections recorded in a single day since a deeply troubling surge in July.

The infection rate has risen steadily since Halloween, reflecting a worrying trend seen on an even worse scale in California and several other parts of the U.S. The death rate hasn’t seen the same sharp rise, something health officials have attributed to advances in medicines and treatments for the virus the past few months.

The Department of Public Health confirmed 20 deaths Saturday, bringing the total number of lives lost to 7,266. Throughout the pandemic, 336,549 infections have been recorded in L.A. County.

As the nation’s most populous county, Los Angeles has fared worse than most of the rest of the state, reporting a disproportionately high number of cases and deaths early in the pandemic. But this month marks the worst surge since mid-July through August, when some days saw more than 2,000 people in hospitals receiving life-saving treatment for the respiratory virus.

Health officials have attributed the spike in infections and deaths following July 4 to celebrations and gatherings over the holiday where the virus was spread among people. Cases since have been generally on the decline — until this month. Hospitalizations have also inched up in November.

County Health Director Barbara Ferrer on Thursday described the recent spike in newly recorded daily cases as a “consistent and significant” increase, telling residents “we all need to act now.”

“If collectively we fail to stop the acceleration of cases, we will have no choice but to look at additional actions,” Ferrer said, not specifying what sorts of restrictions the county may consider.

On Thursday, as the number of California coronavirus cases surpassed 1 million, health officials warned all L.A. County schools and campuses could face a hard closure if conditions don’t improve. So far, 150 cases among staff and students have been reported in outbreaks at 12 schools.

Currently, 966 people are being hospitalized with the virus with about 28% of them being treated in an intensive care unit, health officials said. The number of hospitalizations confirmed Saturday is the highest it has been in nearly two months, according to the Department of Public Health.

In a written statement, the health agency attributed the rising rate of spread of the virus to younger adults — noting that 74% of Saturday’s cases involve patients under the age of 50. Meanwhile, 90% of the deaths recorded Saturday were of people over 50.

“Younger people continue to drive the increase in community transmission in the county,” the statement read. “The rise in cases complicates planning for increasing the numbers of students returning to schools, further re-opening additional sectors and permitting additional activities.”

Los Angeles County remains in the most restrictive stage of California’s reopening plan — the purple tier. During this stage, restaurants, movie theaters and several other businesses are barred from hosting customers indoors since the virus is considered “widespread,” according to state guidelines.

San Bernardino, Riverside and San Diego counties all also remain in the purple tier while Orange and Ventura counties have managed to move into the second-most restrictive red tier. Businesses including restaurants and gyms are allowed to open indoors at this stage with some limitations.

While younger adults make up most new infections, health officials noted that people between 30 and 49 years old make up the highest percentage of new cases: 34%. And people between 18 and 29 years old actually make up just 27% of all new cases.

The upcoming Thanksgiving holiday has put health officials on high alert since the worst surges in cases followed Memorial Day and the Fourth of July. And now, the latest spike has surfaced less than a month after officials warned of Halloween events that could serve as so-called “super-spreaders.”

Ferrer said L.A. County residents should avoid traveling and gathering with more than two other households over Thanksgiving to prevent further spread of the virus. People who travel out-of-state are advised to quarantine for 14 days.

During gatherings, health officials recommend maintaining six feet of physical distance with people from other households at all times, wearing facial coverings and frequently washing one’s hands. They also advise only gathering outdoors for less than two hours at a time.

Ferrer said recent outbreaks at local worksites and resulting spread of the virus amongst family and household members has also contributed to the recent spike. But in the health department statement released Saturday, she said younger adults are also to blame.

“Many younger people are out socializing with non-household members, raising concerns that asymptomatic young people are helping to spread the virus to more vulnerable people at a time when cases are surging dangerously in the county,” Ferrer said in the statement.