UCI study suggests as much as 11.5% of O.C. residents may have already had coronavirus

Antibody testing conducted by UCI and the Orange County Health Care Agency
A study conducted by UCI and the Orange County Health Care Agency found 11.5% of 3,000 randomly selected county residents tested positive for COVID-19-related antibodies.
(Courtesy of Carlos Puma for UCI Health)

While reported cases of coronavirus in Orange County continue on a steady upward trajectory, the true number of people who may have been infected with the virus and recovered without exhibiting symptoms or being tested is thought to be much higher.

A recent study conducted through a partnership between UC Irvine and the Orange County Health Care Agency, the findings of which were released Wednesday, hints at just how much higher that unknown number might be.

Researchers found that the blood of 11.5% of the more than 3,000 random participants sampled at 11 drive-through testing sites tested positive for COVID-19-related antibodies. That figure is about seven times as many people as health officials previously estimated and, when applied to Orange County’s total population of 3.2 million works out to roughly 368,000 residents.

“There was this lurking suspicion that there’s a large fraction of people that have it that did not know,” UCI Public Health Associate Professor Tim Bruckner said in a UCI news report Wednesday. “Either they had no symptoms and did not seek care, or they did not have symptoms and had no reason to go.”

A finger-prick test for COVID-19-specific antibodies.
A finger-prick test allowed UCI researchers to test a random sampling of Orange County residents’ blood for COVID-19-specific antibodies.
(Courtesy of Carlos Puma for UCI Health)

An even higher rate of Orange County Latinos and low-income residents who participated in the UCI study — 17% and 15%, respectively — were found with antibodies indicating they had already been infected with the coronavirus.

It’s unclear what the unnamed diabolical ironclad beetle thought when it was run over by a Toyota Camry.

In a media briefing Thursday, Orange County Health Care Agency Director and Public Health Officer Dr. Clayton Chau said the results of the study were not surprising but do indicate more work is needed to target groups most at risk for infection.

“The survey’s key findings truly point to the need for something that we have known and have been laser focused on tackling and that is the issue of health equity,” Chau said.

In addition to partnering with area organizations who work directly with vulnerable populations, the agency aims to recruit for a director of population health and equity, who would work within all levels of the agency and in affected communities to develop strategies and partnerships designed to improve health outcomes.

“We are looking for someone who really has the ability to engage across sectors as well as listen to the communities in need and respond appropriately,” Chau said of the position.

OCHA officials on Thursday recorded 229 new cases of coronavirus and one death, bringing Orange County’s cumulative case count to 59,442 and the fatality rate to 1,468. Area hospitals reported they were treating 181 individuals for COVID-19, including 59 in intensive care units.

The county’s seven-day average of new cases stood at 5.1 per 100,000 residents, while the average health equity quartile positivity rate hovered at 6% — those figures would need to drop to 3.9 and 5.2% in order for Orange County to move to a less restrictive “orange” reopening tier.

Thursday also saw reporting of 9,102 tests countywide, bringing the cumulative total to 1,091,441 tests issued so far and accounting for a seven-day average testing positivity rate of 3.2%. On Thursday, Chau encouraged residents to get tested regularly.

“There are people walking around asymptomatic, and if they don’t get tested, we don’t know,” he said.

After an Oct. 12 reopening was postponed, officials created a plan to let kids learn from home but stay with their home schools. They also created a COVID-19 dashboard to identify new cases.

Here are the latest cumulative coronavirus case counts and COVID-19 deaths for select cities in Orange County:

  • Santa Ana: 11,471 cases; 315 deaths
  • Anaheim: 10,154 cases; 315 deaths
  • Huntington Beach: 2,600 cases; 86 deaths
  • Costa Mesa: 2,024 cases; 44 deaths
  • Irvine: 1,898 cases; 13 deaths
  • Newport Beach: 1,237 cases; 26 deaths
  • Fountain Valley: 571 cases; 20 deaths
  • Laguna Beach: 250 cases; fewer than five deaths

Here are the case counts by age group, followed by deaths:

  • 0 to 17: 4,420 cases; one death
  • 18 to 24: 8,914 cases; five deaths
  • 25 to 34: 12,771 cases; 21 deaths
  • 35 to 44: 9,467 cases; 38 deaths
  • 45 to 54: 9,569 cases; 114 deaths
  • 55 to 64: 7,140 cases; 205 deaths
  • 65 to 74: 3,578 cases; 289 deaths
  • 75 to 84: 1,976 cases; 318 deaths
  • 85 and older: 1,561 cases; 477 deaths

Updated figures are posted daily at For information on getting tested, visit

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