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LOS ANGELES (Tribune News Service) — Experts are warning that employees might be showing up to work while sick with COVID-19, with symptoms so mild even health care workers are being fooled.

It has long been known that people experiencing mild or no symptoms can spread the coronavirus to others. But health experts are now noting that more people who are experiencing very mild illness are working anyway — exacerbating the transmission risk.

Dr. Ralph Gonzales, a UC San Francisco associate dean, said at a recent campus town hall that the latest dominant omicron subvariant, BA.5, can result in symptoms so mild that health care workers are still working despite the illness. Some people are not testing positive until four or five days after they start showing symptoms of COVID-19.

"We are seeing more employees having been on site with multiple days of symptoms. So please try not to work with symptoms — even if they're mild — because we are seeing quite a bit of mild symptoms with BA.5, and people often don't even realize they're sick," Gonzales said.

While case counts are down markedly from the heights of the latest wave, the risk of exposure remains high. Almost every California county has a high rate of coronavirus transmission, defined as having 100 or more cases a week for every 100,000 residents.

When case rates are at this level, "it's still recommended to layer in precautions that we have all become familiar with during the pandemic, including masking indoors, staying home and getting tested when ill, making good use of the outdoors and maximizing ventilation indoors and getting tested before gathering where people of vulnerable health may be present in order to protect them," Los Angeles County Health Officer Dr. Muntu Davis said Thursday.

The number of L.A. County worksites reporting clusters of coronavirus cases continues to fall; there were 144 in the most recent week, down from the prior week's tally of 152.

At sites where there are outbreaks, Davis said, factors that typically increase the spread of illness are people at work who aren't aware they have a coronavirus infection and a lack of masking.

That's "why it's really important for people to ensure that if they feel sick, even with mild symptoms, to test themselves and make sure that they don't have COVID," he said. "There have been some studies that have shown in the past that even up to about 56% of people didn't know they had an infection."

That's especially vital now as the omicron variant and its family of substrains have proved particularly difficult to avoid — even for those who have long dodged a coronavirus infection.

A review of infections from UC San Francisco's Office of Population Health found that through the beginning of 2022, less than 10% of the campus' employees and students had a prior COVID-19 illness, Gonzales said. But the various waves of the ultra-contagious omicron variants radically changed the cumulative infection rate.

By the beginning of spring, 20% of the university's employees and students had had a coronavirus infection, according to data shared by Gonzales. And by midsummer, 45% had been infected, Gonzales said.

An Axios/Ipsos poll recently said that about half of U.S. adults have had a coronavirus infection at some point.

The most recent seroprevalence estimate for California — the share of residents thought to have been infected with the coronavirus at some point — was 55.5% in February, according to data from the U.S. Centers for Disease Control and Prevention. That was up markedly from an estimated 25.3% last November, prior to omicron's widespread arrival.

The proportion of Californians infected at some point has almost assuredly continued to climb throughout this year, given the steady spate of newly reported infections.

Meanwhile, the pandemic's impact on hospitals has declined as the summer omicron surge has faded.

As of Thursday, there were only seven California counties with a high COVID-19 community level as defined by the CDC, which generally indicates both a high case rate and elevated level of new weekly coronavirus-positive hospital admissions.

The counties still in the high COVID-19 community level as of Thursday — Kern, Ventura, Monterey, Merced, Imperial, Madera and Kings — are home to about 2.9 million Californians, representing about 8% of the state's population. By contrast, two weeks ago, there were 14.4 million Californians living in the 21 counties in the high COVID-19 community level.

Counties that exited the high COVID-19 community level this week were Fresno, San Joaquin, Stanislaus, Humboldt, Sutter, Yuba, San Benito and Tuolumne. Those that exited the level the prior week were Orange, Santa Clara, Alameda, Contra Costa, San Mateo, Santa Barbara, Solano, San Luis Obispo, Napa and Mendocino.

Southern California counties in the medium COVID-19 community level include Los Angeles, San Diego, Orange, San Bernardino and Santa Barbara. Riverside County is in the low COVID-19 community level.

As of Friday, Los Angeles County was recording about 3,000 coronavirus cases a day for the prior seven-day period — less than half the summer peak of nearly 6,900 cases per day, though still far above the springtime low of about 600 cases a day.

On a per capita basis, L.A. County is reporting 206 coronavirus cases a week for every 100,000 residents.

Coronavirus-positive hospitalizations are trending lower. As of Thursday, there were 827 coronavirus-positive hospital patients in L.A. County's 92 hospitals, a 12% decrease over the prior seven days. State models project continued declines over the next month.

L.A. County reported 96 COVID-19 deaths for the seven-day period that ended Friday, 16% higher than the prior week's count of 83. The peak weekly tally for the summer was between July 31 and Aug. 6, when L.A. County reported 122 COVID-19 deaths.

More than 33,000 cumulative COVID-19 deaths have been reported in L.A. County since the pandemic began, including roughly 1,500 over the last five months. Prior to the pandemic, about 1,500 Angelenos typically died from the flu over the course of an entire year.

Some experts are expecting a fall-and-winter COVID-19 wave, as has occurred in the last two years, but it's unclear how bad it may be. Officials are also concerned about the possible return of a significant flu season for the first time in the pandemic era.

The White House has signaled it expects a new omicron-specific booster shot to become available in September. Health officials are urging people to get their flu shot and be up to date on their COVID-19 vaccines ahead of the winter.

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