Coronavirus antibody testing shows LA County outbreak is up to 55 times bigger than reported cases

The Covid-19 outbreak in Los Angeles County is likely far more widespread than previously thought, up to an estimated 55 times bigger than the number of confirmed cases, according to new research from the University of Southern California and the L.A. Department of Public Health.

USC and the health department released preliminary study results that found that an estimated 4.1{3c4481f38fc19dde56b7b1f4329b509c88239ba5565146922180ec5012de023f} of the county’s adult population has antibodies to the coronavirus, estimating that between 221,000 adults to 442,000 adults in the county have had the infection. 

This new estimate is 28 to 55 times higher than the 7,994 confirmed cases of Covid-19 reported to the county through early April. The number of coronavirus-related deaths in the county has now surpassed 600, according to the Department of Public Health. The data, if correct, would mean that the county’s fatality rate is lower than originally thought.

The results are based on antibody testing of about 863 people who were representative of L.A. County, the researchers said. 

“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, in a statement.

With just just 4{3c4481f38fc19dde56b7b1f4329b509c88239ba5565146922180ec5012de023f} of the population infected with the disease, L.A. County is still very early in the epidemic, said USC Professor Dr. Neeraj Sood, who led the study. “Many more people in L.A. County could potentially be infected and as those number of infections rise, so will the number of deaths, the number of hospitalizations and the number of ICU admissions,” he said. 

Sood said the chance someone tested positive for the anitbodies but didn’t actually have Covid-19 was low. They used tests from Premier Biotech, a Minneapolis-based company. 

On Sunday, New York Gov. Andrew Cuomo said the U.S. Food and Drug Administration approved the state’s antibody test, and the state will conduct “thousands” of tests this week. The antibody tests will give the state its “first true snapshot” of how many people in the state have been infected with Covid-19, he said. 

“We don’t really know how many people were infected. How many people had coronavirus but self-resolved. We don’t really know because we haven’t been able to do testing on that large of scale,” Cuomo said. 

Global health officials have questioned if antibody testing can accurately determine whether a person has any immunity to the disease. The World Health Organization issued a warning Friday saying there’s no evidence serological tests can show whether a person has immunity or is no longer at risk of becoming reinfected.

Dr. Mike Ryan, executive director of WHO’s emergencies program, said scientists are also studying how long any potential immunity might last.