A carefully designed study of blood samples from Orange County residents found that 12% had coronavirus antibodies — meaning their immune systems had fought the virus at some point — an infection rate more than seven times higher than official case counts suggest.
That means at least 371,000 people in Orange County have had COVID-19, researchers found.
Rates were highest among Latino residents and low-income adults, and lowest among non-Latino White and Black residents and those earning more than $100,000 a year.
The results also suggest that the virus is extraordinarily contagious and far more widespread than case data indicate, but also that the fatality rate is much lower. Still, it remains higher than the seasonal flu.
“What was most surprising among the researchers was how high the seroprevalence of COVID was,” said Tim Bruckner, a study principal and associate professor of public health at UC Irvine. “We had a suspicion there would be more cases if we looked in the overall community rather than just at those asking for testing, but we didn’t understand how widespread it was already.”
The majority of people studied who tested positive had no symptoms, Bruckner said. Focus may fall on so-called “superspreader” events, but the virus really is spreading regularly, quietly, unseen.
While more than 10% of Orange County residents tested over the summer had COVID-19 antibodies, that’s still a long way from “herd immunity,” when so many people have antibodies that the virus runs out of new hosts. Scientists say some 60% to 70% of the population must be immune before infections will fizzle out.
“We are nowhere near herd immunity,” Bruckner said. “The argument that we’re very close and will turn the corner soon isn’t borne out by the data.”
A city-size case load
The prospect that more people have caught coronavirus in Orange County than live in Anaheim, its largest city, didn’t surprise Dr. Matt Zahn, medical director of the county Health Care Agency’s Communicable Disease Control Division.
“That number is simultaneously a very large and very small number,” Zahn said during a news conference Wednesday, Oct. 28.
It’s research-backed evidence of how easily COVID-19 spreads, he said. At the same time, it shows that the virus still has lots of room to proliferate.
For Bernadette Boden-Albala, dean of UC Irvine’s public health program, an expert in social epidemiology and study principal, it also speaks to the fact that there’s huge variability in how people show symptoms, if at all.
“Obviously, we hear about the most severe cases, the hospitalized cases, the deaths, but we have this whole range of asymptomatic and mild symptoms that didn’t get picked up because people didn’t think they were sick and were transmitting the disease,” she said.
“This is really important data to help us think about planning for the future.”
More evidence of health inequity
While data from active infections already show that lower-income and Latino communities are hard hit by infection, the study underscored that in a powerful way.
Latino residents had a prevalence of 17%, and low-income residents were at 15%. That could be due to relatively dense housing conditions and work in settings that don’t allow for physical distancing, the study said.
That tracks with high-volume swab testing in lower-income Latino neighborhoods in Anaheim and Santa Ana.
“In a city like Santa Ana, we were as high as close to 30% positivity,” Boden-Albala said.
The disproportionately high rates of tests returning positive in the county’s hot spots have been tamped down by the Orange County Health Care Agency in partnership with nonprofit groups like Latino Health Access, Boden-Albala said. Such campaigns have brought more testing and resources to neighborhoods where many residents can’t work from home and have little access to health care.
Public health officials on Oct. 6 installed coronavirus disparities tracking into the state’s four-tier pandemic monitoring system, which looks at metrics such as case rates and testing positivity in the state’s 58 counties and determines what can reopen when.
More prevalent, less deadly
Case data — drawn from sick people who wind up at diagnostic testing sites, clinics and hospitals — peg the COVID death rate at about 10% for those 65 and older in Orange County.
“That’s another part of the story that’s very interesting,” Bruckner said. “Clearly, COVID is a killer and I would never want to make light of that. That said, as you count more cases that are asymptomatic and lightly symptomatic, the case fatality rate is going to go down.
“The take-home point is that, depending on the different ways you’d calculate COVID deaths, we’re overestimating deaths in OC between four- to 10-fold.”
Put more simply, the study estimates about one death per thousand infected people for those younger than 65, and about 10 deaths per thousand for those 65 and older.
“Based on our estimates, that means about 1 in 100 adults over 65 who gets COVID dies of it,” Bruckner said. “That’s pretty serious. But it’s not 10 in 100, which is the estimate based on who presents at the clinic.”
Recommendations
The widespread prevalence of COVID in Orange County warrants continued public health measures, the study said: physical distancing, proper and consistent use of face masks, ventilation and hand hygiene.
And, in addition to contact tracing, county health authorities “may want to consider active surveillance of novel infections.” That would involve some 800 to 1,000 tests per week in a representative sample of residents, as well as a targeted component for higher-risk groups or places such as nursing home residents, laborers in high-density settings and highly impacted neighborhoods.
“Such surveillance, unlike clinic- or hospital-based strategies, would provide a less biased estimate of the rate of new SARS-CoV-2 infections,” the study said.
Finally, as fatality rate estimates are several-fold lower, “This updated estimate should inform the broader policy debate in the U.S. regarding the relative benefits and limitations of various SARS-CoV-2 mitigation strategies.”
How it was done
UCI researchers led the project in partnership with the OC Health Care Agency, which provided funding, testing sites and input on the study’s survey methods.
It was designed to be more comprehensive and rigorous than its predecessors, including many more people than were tested in L.A. or Santa Clara counties. Researchers went to the homes of people who couldn’t make it to drive-through sites, with a special eye toward reaching under-served communities, and didn’t initially indicate they’d be offering blood, or serology, tests, to avoid pre-selecting for people who might want them.
Fingers were pricked and blood collected from 2,979 adults from July 10 to Aug. 16, later in the pandemic than similar studies done in Los Angeles and Santa Clara counties in the spring. Researchers at UCI are planning more work on racial and ethnic disparities, geographic hot spots, and tracking people who’ve tested positive over time to see how long immunity lasts.
Neeraj Sood, professor of public policy at the USC Price School for Public Policy and principal investigator for the groundbreaking serology study done by USC and the Los Angeles County Department of Public Health in the spring, said that’s one of the outstanding questions.
“The level of antibodies you have, and how fast they decline, might correlate with how severe your disease was,” said Sood, who’s also planning to study people who’ve tested positive over time in L.A. County. “There’s more and more evidence which suggests seroprevalence declines over time. So even serological testing might be underestimating the true prevalence — we might only be catching infections over the last few months, rather than since the pandemic began.”
A big takeaway from O.C.’s work is that many people had COVID and didn’t know it, supporting the notion that the virus is a silent spreader, said UCI’s Bruckner. “Ongoing public health strategies that relate to the whole population — and not just those who think they’re sick — are warranted,” he said.
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Study finds 12% of Orange County residents had coronavirus by summer - OCRegister
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