Hundreds of thousands of people may have already been infected by the coronavirus in Los Angeles County, up to 55 times more than current testing shows, according to a new study by the USC and the Los Angeles County Department of Public Health.
Based on a preliminary survey that tested around 863 people, about 4.1% tested positive for COVID-19 antibodies, which indicates they were infected with the coronavirus at some point.
This antibody test is different than tests health officials are running on a more widespread basis, which only shows whether someone is currently infected with the disease.
When factoring in the reliability of the antibody test, researchers estimated between 2.8% and 5.6% of LA County’s adult residents may have already been infected by the coronavirus at some point.
That translates to somewhere between 221,000 and 442,000 LA County residents. Those figures are 28 to 55 times higher than the number of cases health officials have been able to confirm through conventional testing.
Based on that conventional testing, the county had only confirmed 7,994 cases of COVID-19 at the time of the study. That number is now up to 13,816 cases and more than 600 deaths.
LA County Health Director Barbara Ferrer said these results reinforce the need for physical distancing and stay-at-home orders, “because there are many, many people throughout the county, who are positive for COVID-19 who may not be showing any symptoms.”
Ferrer said USC and the county will expand the study over the next few months to try to confirm or improve their findings.
“Again, this data is preliminary,” she said.
Ferrer also cautioned that testing positive for COVID-19 antibodies doesn’t necessarily mean someone is immune or protected from the disease in the future.
If there’s a glimmer of hope from the new study, Ferrer said it shows the true mortality rate for COVID-19 is likely much lower locally than previously estimated. However, she said, it still appears to be more deadly than the flu.
Researchers used a marketing firm to select a random sampling of people for the study that was representative of LA County’s demographics, according to Ferrer.
“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,” said the lead investigator on the study, USC professor Neeraj Sood of the USC Price School for Public Policy. “The estimates also suggest that we might have to recalibrate disease prediction models and rethink public health strategies.”
The numbers, he said, prove that “we are very early in the epidemic.” Even if 5.6% of LA County residents have already been infected, that means almost 95% of people still haven’t, Ferrer noted.