Hundreds of thousands of LA County residents may have coronavirus, USC antibody study suggests

First round of antibody tests released

Startling results from antibody testing. Suggests the coronavirus may have infected far more people than we ever thought.

LOS ANGELES - Researchers at the University of Southern California and the Los Angeles County Department of Public Health on Monday released their initial findings from an antibody study, which suggests that hundreds of thousands of L.A. County residents may have developed coronavirus antibodies.

While researchers say this doesn't mean that an individual is immune to the virus, it does provide health officials with deeper insight into the virus and its spread across the county.

The study suggests that the number of L.A. County residents infected with the coronavirus far exceeds the number of confirmed cases, meaning there are potentially hundreds of thousands of residents who are unknowingly infected with the illness and not showing any symptoms, but are still capable of spreading it to others.

The numbers prove that "we are very early in the epidemic," said USC professor Neeraj Sood of the USC Price School for Public Policy, who is spearheading the study.

Dr. Neeraj Sood talks USC Antibody study

The USC Price School of Public Policy details university's antibody study.

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The county's public health director, Dr. Barbara Ferrer, said that based on the data, the county's social-distancing requirements need to remain in place.

"These findings underscore the importance of expanded polymerase chain reaction (PCR) testing to diagnose those with infection so they can be isolated and quarantined, while also maintaining the broad social distancing interventions," Ferrer said.

The antibody test is helpful for identifying past infection, but a PCR test is required to diagnose current infection.

Based on the results of the first round of testing, which was conducted on 863 adults in the county, the researchers estimate that 4.1% of the county's adult population has an antibody to the virus, meaning they have SARS-CoV-2 antibodies in their bloodstream.

"Adjusting this estimate for statistical margin of error implies about 2.8% to 5.6% of the county's adult population has antibody to the virus- which translates to approximately 221,000 to 442,000 adults in the county who have had the infection. That estimate is 28 to 55 times higher than the 7,994 confirmed cases of COVID-19 reported to the county by the time of the study in early April," USC said in a press release on the findings.

The initial findings also suggest that the county's mortality rate is much lower than county officials believed since the rate of mortality has been calculated using the number of confirmed county cases, rather than the number of potentially infected individuals in the county.

"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 L.A. County Department of Public Health and co-lead on the study.

Researchers at USC say that updated estimates to the COVID-19 mortality rate can help lawmakers assess whether to keep stay-at-home orders and social distancing measures in place and for how long.

The first round of testing was conducted on April 10 and 11. The individuals selected for the study were selected at random by the market services firm LRW Group. The firm used a large proprietary database to ensure factors such as age, race and sex were part of the random selection.

There are still questions about the accuracy of these tests, which have not yet been approved by the Food and Drug Administration.

USC's antibody test was manufactured by Premier Biotech and has tested blood from COVID-19-positive patients with a 90 to 95% accuracy rate. However, researchers at USC still say it's unclear if the tests can check for immunity.

"COVID-19 is a new disease, so we don’t know the extent to which tests identify neutralizing antibodies and the extent to which antibodies give immunity. Even if some immunity is conferred, we don’t know how long this immunity lasts," Sood said in a USC release.

According to Sood, prior to the antibody testing, data on the virus has been dependent on confirmed COVID-19 cases, which relies on tests that detect active infection. This “selection bias” doesn’t give researches the full picture when they work to understand the virus, he said.

The study's results have not yet been peer-reviewed by other scientists. The researchers plan to test new groups of participants every few weeks in the coming months to gauge the pandemic's trajectory in the region.

In early April, researchers at Standford University tested a group of 3,330 adults and children in Santa Clara County for SARS-CoV-2 antibodies. The study found that the population prevalence of COVID-19 in Santa Clara ranged from 2.49 percent to 4.16 percent, meaning that the virus could be more widespread than previously thought.

“The most important implication of these findings is that the number of infections is much greater than the reported number of cases,” the researchers wrote. “Our data imply that, by April 1 (three days prior to the end of our survey) between 48,000 and 81,000 people had been infected in Santa Clara County. The reported number of confirmed positive cases in the county on April 1 was 956, 50-85-fold lower than the number of infectious predicted by this study.”

Neither serology test has been approved yet by the FDA.