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SAN DIEGO — San Diego residents should mask up indoors, according to the Centers for Disease Control and Prevention, which moved the county back into its highest level of local concern Thursday.

The agency evaluates COVID-19 community levels every seven days, and San Diego County entered the “high” category this week. It had been listed as “medium” since May.

Health experts base the metric on three different factors: New hospital admissions per 100,000 people, the percent of staffed inpatient beds occupied by COVID-19 patients and total new cases per 100,000 people.

A map of California’s COVID-19 community levels as defined by the CDC. Red counties are in the “high” category, with masks recommended indoors. (Photo: CDC)

In areas with high COVID-19 levels, the CDC recommends that everyone, “wear a well-fitting mask indoors in public, regardless of vaccination status.”

Anyone at risk for severe illness should consider taking additional precautions, the agency says. That includes staying 6 feet away from others, avoiding crowds and poorly ventilated spaces, and washing their hands often.

The CDC has recommended masks indoors in a majority of California counties since the end of June, but populous Los Angeles, San Diego and Orange counties initially avoided the “high” community level. All three regions entered the category this week.

In Los Angeles, that will trigger a universal indoor masking mandate if it remains the case for more than two weeks, according to local officials.

San Diego County leaders have not outlined a similar trigger for local mask mandates based on the CDC metric.

In a statement reacting to the news, local officials cited “recent spikes in hospitalizations and new cases.”

The county said people who have COVID-19 should know that treatments are now available. Local clinics and pharmacies offer oral medications, taken as pills, and monoclonal antibodies in the form of IV infusions.

The medications require a doctor’s prescription and should be started within five days of developing symptoms, officials wrote. To determine if such a treatment makes sense for you, talk to your health care provider or call 2-1-1 to find a doctor, the county said.

Federal health experts urged all Californians to get vaccinated and boosted, and to get a coronavirus test if they have symptoms. The CDC adds that “people may choose to mask at any time” regardless of community level, and that anyone “with symptoms, a positive test, or exposure to someone with COVID-19 should wear a mask.”

You can view complete state- and county-level data on the CDC’s website.

FOX 5’s Milo Loftin contributed to this report.