The results are from the first round of an ongoing study by USC researchers and county health officials. They will be conducting antibody testing over time on a series of representative samples of adults to determine the scope and spread of the pandemic across the county.
Based on the results of the first round of testing, the research team estimates that approximately 4.1% of the county's adult population has an antibody to the virus. Adjusting this estimate for the statistical margin of error implies about 2.8% to 5.6% of the county's adult population has an antibody to the virus — which translates to approximately 221,000 to 442,000 adults in the county who have been infected. That estimate is 28 to 55 times higher than the 7,994 confirmed cases of COVID-19 reported to the county at the time of the study in early April. The number of COVID-related deaths in the county has now surpassed 600.
"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 lead investigator Neeraj Sood, professor of public policy at the USC Price School for Public Policy and senior fellow at the USC Schaeffer Center for Health Policy and Economics. "The estimates also suggest that we might have to recalibrate disease prediction models and rethink public health strategies."
What do the antibody testing results mean for controlling COVID-19?
The results have important implications for public health efforts to control the local epidemic.
"These results indicate that many persons may have been unknowingly infected and at risk of transmitting the virus to others," said Barbara Ferrer, director of the L.A. County Department of Public Health. "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."
The antibody test is helpful for identifying past infection, but a PCR test is required to diagnose a current infection.
"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 Paul Simon, chief science officer at the L.A. County Department of Public Health and co-lead on the study.
Comment: It also suggests that the lockdown measures probably aren't as effective as people think. The decision to socially isolate should be an autonomous choice, not the result of government coercion. Either way, this virus will spread through the population, run its course, and humanity will live on. It's not the black death, or anywhere near approaching that level of risk and destruction.
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.
With help from medical students from the Keck School of Medicine of USC, USC researchers and public health officials conducted drive-thru antibody testing on April 10 and 11 at six sites. Participants were recruited via a proprietary database that is representative of the county population. The database is maintained by LRW Group, a market research firm.
The researchers used a rapid antibody test for the study. The FDA allows such tests for public health surveillance to gain greater clarity on actual infection rates. The test's accuracy was further assessed at a lab at Stanford University using blood samples that were positive and negative for COVID-19.
In addition to Sood and Simon, other authors and institutions contributing to the study include Peggy Ebner of the Keck School of Medicine, Daniel Eichner of the Sports Medicine Research and Testing Laboratory, Jeffrey Reynolds of LRW Group and Eran Bendavid and Jay Bhattacharya of the Stanford University School of Medicine.
The study was supported by funding from the USC Schwarzenegger Institute for State and Global Policy, the USC Lusk Center for Real Estate, the USC president's office, the Jedel Family Foundation, LRW Group, SoapBoxSample and several individual donors.
Comment: As more time passes, more stats come out, painting a clearer picture (which is still murky, however). More people are infected, the death rate is lower than previously believed. Voice of America reports that perhaps 25% of Americans may already have it, the vast majority showing mild or no symptoms. And up to 70% of the military may already have had it. Another study suggests something similar for Sweden, where at least 11% of the population are believed to have contracted the virus. Iceland screened 6% of its population and only 0.7% tested positive. Yet here's an anomaly: a French boy who had the virus somehow didn't manage to pass it on to any of the 172 people he came into contact with.
As for deaths, there are contradictory bits of information. On the one hand, doctors are being encouraged to list Covid-19 as the cause of death for practically anyone (if they're dead and test positive, count it as a Covid-19 death). This suggests the death numbers are inflated. Yet many hard-hit areas (like NYC, London, Bergamo, etc.) have seen a large spike in mortality over the past month or two, and not all of these excess deaths have been attributed to Covid-19. Official numbers released by the UK government don't even include all deaths attributed to Covid-19 - just those who die in hospital.
It will be a while before we can say anything with certainty about the extent of Covid-19 and unrelated deaths in said areas.