Hundreds of thousands of Los Angeles County residents may have been infected with the coronavirus by early April, far outpacing the number of officially confirmed cases, according to a report released Monday.
The initial results from the first large-scale study tracking the spread of the coronavirus in the county found that 2.8% to 5.6% of adults have antibodies to the virus in their blood, an indication of past exposure.
That translates to roughly 221,000 to 442,000 adults who have recovered from an infection, according to the researchers conducting the study, even though the county had reported fewer than 8,000 cases at that time.
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A person drops a specimen at a new COVID-19 mobile testing site in Bell.
(Christina House/Los Angeles Times)
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A person swabs their mouth at a new COVID-19 mobile testing site in Bell.
(Christina House/Los Angeles Times)
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A man talks with a healthcare worker outside Kedren Community Health Center in South LA, where they are offering walk-up coronavirus testing along with other medical services.
(Jason Armond/Los Angeles Times)
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A specimen is turned in at the new mobile testing site for people with symptoms of the coronavirus at Charles R. Drew University of Medicine and Science in South Los Angeles.
(Christina House/Los Angeles Times)
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A portrait and quote by Martin Luther King, Jr. overlooks a new mobile testing site for people with symptoms of the coronavirus at Charles R. Drew University of Medicine and Science in South Los Angeles.
(Christina House/Los Angeles Times)
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Julie Montez, right, sits in her car as a nurse administers a coronavirus test at Arrowhead Regional Medical Center in Colton.
(Irfan Khan/Los Angeles Times)
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Nurses pose for a fun photo between breaks at a drive-through public testing for coronavirus at Arrowhead Regional Medical Center in Colton.
(Irfan Khan/Los Angeles Times)
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Healthcare workers tend to a driver in line at a drive-through Coronavirus (COVID-19) testing site at the Westminster Mall in Westminster.
(Allen J. Schaben/Los Angeles Times)
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Healthcare workers tend to a driver in line at a drive-through Coronavirus testing site at the Westminster Mall in Westminster.
(Allen J. Schaben/Los Angeles Times)
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Juan Infante, a certified medical assistant, takes the temperature of a patient before she gets tested for Covid-19.
(Carolyn Cole/Los Angeles Times)
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Gessie Lurlay is working as a coronavirus screener at the Camarena Health Center in Madera.
(Carolyn Cole/Los Angeles Times)
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Francis Gon-Gibbs, of LA County Fire Department Lifeguard Division, stands at the entrance of a new mobile testing site for people with symptoms of the coronavirus at Charles R. Drew University of Medicine and Science in South Los Angeles.
(Christina House/Los Angeles Times)
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A man drops off his self-administered COVID-19 test in a blue bin at a drive-up test site at the Veterans Administration Parking Lot 15 outside of Jackie Robinson Stadium in Los Angeles.
(Genaro Molina/Genaro Molina/Los Angeles Times)
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Workers direct drivers at a drive-up test site for COVID-19 at the Veterans Administration Parking Lot 15 outside of Jackie Robinson Stadium in Los Angeles.
(Genaro Molina/Los Angeles Times)
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A man misses the blue bin while dropping off his self-administered COVID-19 test at a drive-up test site at the Veterans Administration Parking Lot 15 outside of Jackie Robinson Stadium in Los Angeles.
(Genaro Molina/Los Angeles Times)
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Workers help conduct drive-thru coronavirus testing at Crenshaw Christian Center in South Los Angeles.
(Jason Armond/Los Angeles Times)
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A sign directs people to drive-thru coronavirus testing at Crenshaw Christian Center in South Los Angeles.
(Jason Armond/Los Angeles Times)
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Cassidy Roosen, with Beach Cities Health District, holds up a sign that says, “We’re All In This Together,” while waiting to direct cars at a drive-through, appointment-only coronavirus testing location, at the South Bay Galleria, in Redondo Beach.
(Jay L. Clendenin/Los Angeles Times)
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A woman shows her notice from her doctor that allows her to obtain a test for COVID-19 at a new drive-up testing site in a parking lot at the South Bay Galleria in Redondo Beach.
(Genaro Molina/Los Angeles Times)
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Coronavirus CO drive-thru sample collection takes place at the county fairgrounds in Victorville.
(Irfan Khan/Irfan Khan/Los Angeles Times)
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San Bernardino County health care worker takes a sample at a coronavirus drive-thru sample collection that took place at the county fairgrounds in Victorville.
(Irfan Khan/Los Angeles Times)
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Motorists, line up on Stadium Way, near Dodger Stadium, waiting to enter a parking lot and be tested for the coronavirus.
(Mel Melcon/Los Angeles Times)
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Members of the Los Angeles Fire Dept. wear protective gear while handing out kits to people to swab the inside of their mouths to test for the coronavirus, inside a parking lot on Stadium Way, near Dodger Stadium.
(Mel Melcon/Los Angeles Times)
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Riverside County medical personnel screen a car of load of four people at a coronavirus drive-though testing facility for Coachella Valley residents in the parking lot of the Southwest in Indian Wells.
(Gina Ferazzi/Los Angeles Times)
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Aerial views cars lined up for drive-through coronavirus testing inside a parking lot on Stadium Way near Dodger Stadium.
(Robert Gauthier/Los Angeles Times)
“We haven’t known the true extent of COVID-19 infections in our community because we have only tested people with symptoms, and the availability of tests has been limited,” study leader Neeraj Sood, a professor at USC‘s Price School for Public Policy, said in a statement. “The estimates also suggest that we might have to re-calibrate disease prediction models and rethink public health strategies.”
The early results from L.A. County come three days after Stanford researchers reported that the coronavirus appears to have circulated much more widely in Santa Clara County than previously thought.
The Stanford team estimated that 2.5% to 4.2% of Santa Clara County residents had antibodies to the coronavirus in their blood by early April.
Though the county had reported roughly 1,000 cases in early April, the Stanford researchers estimate the actual number was 48,000 to 81,000, or 50 to 85 times greater.
The Santa Clara study recruited around 3,300 participants from social media, which has raised some concerns that the results may not be representative of the county as a whole. The researchers made adjustments to their data to account for that problem.
The study was composed differently in Los Angeles; participants were selected through a market research firm to represent the makeup of the county. The county and USC researchers intend to repeat the study every two to three weeks for several months, in order to track the trajectory of the virus’ spread.
Both counties used rapid antibody tests supplied from Premier Biotech, a Minneapolis-based company. The test has not yet been approved by the FDA, although the federal government does allow for such tests to be used for public health surveillance.
As antibody testing, also known as serological tests, has risen in prominence, so too have concerns about accuracy over the results.
The L.A. County Public Health Department cautioned healthcare providers last week against interpreting results from such tests “until there is additional data on their best use because of concerns of both false negative and false positive results.”
Nevertheless, antibody tests have increasingly become a focal point in the response to coronavirus because they can potentially show the true extent of the virus’ reach and therefore can shed light on how close the population is to achieving herd immunity, in which enough people have some degree of immunity to the virus that it becomes difficult for infections to spread.
Such tests can also provide a more accurate picture of how lethal the virus is. Right now, the mortality rate is based on the number of confirmed infections, but the higher the number of infections, the lower the fatality rate.
“Though the results indicate a lower risk of death among those with infection than was previously thought, the number of COVID-related deaths each day continues to mount, highlighting the need for continued vigorous prevention and control efforts,” said Dr. Paul Simon, chief science officer at the L.A. County Department of Public Health and co-lead on the study.
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