TUESDAY, April 21, 2020 (HealthDay News) -- An early analysis of antibody testing from Los Angeles County finds a coronavirus infection rate that is up to 55 times the number of confirmed COVID-19 cases.
According to the researchers behind the study, the vast majority of people infected with the new coronavirus may be going without symptoms or have minimal symptoms.
It's one of the first in-depth analyses of local population infection rates conducted in the United States.
Los Angeles County's population totals more than 10 million. As the research team noted, by early April, there were 7,994 confirmed cases of COVID-19 reported in the county, including 600 COVID-19 deaths.
But new findings from the first round of ongoing antibody blood testing of county residents showed that about 4.1% of adults had antibodies to the coronavirus.
Adjusting for any statistical margin of error, that suggests that between 2.8% to 5.6% of the county's adults have antibodies to the coronavirus, which translates to between 221,000 to 442,000 adults in Los Angeles County having already had the infection.
That estimate is 28 to 55 times higher than the number of confirmed cases of COVID-19 reported to the county by the time of the study in early April, said researchers from the University of Southern California (USC) and the Los Angeles County Department of Public Health.
"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," lead investigator Neeraj Sood, professor of public policy and senior fellow at the Center for Health Policy and Economics at USC, explained in a university news release.
Now that the true, and much wider, penetration of coronavirus within the general public is known, "we might have to recalibrate disease prediction models and rethink public health strategies," Sood said.
Dr. Barbara Ferrer directs the L.A. County Department of Public Health. Speaking in the news release, she said the antibody test results "indicate that many persons may have been unknowingly infected and at risk of transmitting the virus to others."
The study also highlights the need for expanded polymerase chain reaction (PCR) testing, she said, so infected individuals "can be isolated and quarantined, while also maintaining the broad social distancing interventions." The antibody test can help detect past coronavirus infection, but a PCR test is required to diagnose current infection, Ferrer explained.
According to study co-leader Dr. Paul Simon, chief science officer at L.A. County Department of Public Health, "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."
The researchers plan to test new groups of people every few weeks over the coming months to assess the pandemic's spread in the county.
The U.S. Centers for Disease Control and Prevention has more on COVID-19.
SOURCE: University of Southern California, news release, April 20, 2020