RIVERSIDE COUNTY, CA —Riverside County health officials said Monday that preliminary data from a recent Riverside University Health System COVID-19 antibody testing study show well over 100,000 county residents have likely been infected with the virus but they were never accounted for.
The randomized study of 1,726 county residents — the results of which are still being analyzed — was conducted over two weekends in July and included children (5 years and older) and adults. Researchers wanted to know whether the individuals had been exposed to coronavirus and developed COVID-19 antibodies. Initially, 3,500 individuals were sought for the study.
Of the, 1,726 people tested, 101 of them showed they had developed antibodies for COVID-19 — a positivity rate of 5.9 percent. Negative tests numbered 1,621, and four tests came back with unclear results, according to RUHS.
"Based on that data, it is estimated there have been between 118,000 and 175,400 infections in Riverside County," according to RUHS. As of Monday afternoon, 35,187 infections have been reported countywide.
It's not clear how many of those who showed they had developed antibodies were asymptomatic when infected. On Friday, Dr. Geoffrey Leung, Riverside University Health System-Medical Center, said asymptomatic carriers are greatly contributing to the uptick in new coronavirus cases.
"Forty percent of spread is silent spread," he said.
Residents could not volunteer for the antibodies study, in part, because health officials wanted a more representative sampling of the community, officials said.
“We believe the number and variety of participants shows the study successfully recruited an excellent representation of the community and accurately reflects the prevalence of the antibody in Riverside County,” said Dr. Tait Stevens, with Riverside University Health System and co-author of the study.
The medical community does not yet know the extent of the benefits of testing positive for coronavirus antibodies. For example, it is not yet known if someone can contract the virus again after testing positive for antibodies, and how long any protection might last.
County officials said the study underscores the need to wear face coverings as people may have the virus without any symptoms, then easily spread it to others when not wearing a mask or keeping six feet of distance.
“We continue to learn new information about coronavirus, and this survey adds important research to the growing knowledge of COVID-19,” said Riverside County Board Chair and Fourth District Supervisor V. Manuel Perez. “We still must protect everybody out there who is susceptible to getting sick, and we should do so by wearing face coverings, physical distancing, washing our hands and avoiding gatherings.”
The county's public health department is not creating a list of study participants and will not collect the individual information from the research, officials said.
A final study report has not yet been released by county officials.