The number of people infected with COVID-19 in Riverside County may be at least three times as high as the official tally, according to antibody testing results released Monday by public health officials.
Officials estimate there have been between 118,000 and 175,400 infections countywide based on randomized serology testing conducted earlier this month.
The study involved 1,726 county residents, 101 of whom tested positive for COVID-19 antibodies — a positivity rate of about 6%, according to a news release.
That’s at least a 235% increase over the 35,187 cases confirmed in the county through diagnostic tests.
Last week, the U.S. Centers for Disease Control and Prevention released data showing the number of coronavirus infections nationwide is much greater than the official count — between 2 and 24 times higher, depending on the region. In the Bay Area, the real number of infections is estimated to be at least 9 times higher.
The antibody or serology tests are meant to determine if someone has had a previous immune response to the virus — meaning their immune system worked to fight it off. Antibodies developed to do so stay in the blood after the infection is over.
Scientists are still working to understand antibodies for the new coronavirus.
The latest research suggests COVID-19 antibodies fade within a few months — meaning they may not help in staving off new infections. But antibodies are only part of the body’s defense, and experts say they the immune system may remember how to make fresh antibodies.
“We continue to learn new information about coronavirus, and this survey adds important research to the growing knowledge of COVID-19,” Riverside County Board of Supervisors Chair V. Manuel Perez said in a statement. “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.”
Officials noted that the study results are still being analyzed, and they had originally hoped to test a larger pool of 3,500 individuals. However, they added that their survey was unique in including both adults and children at least 5 years old.
Residents were randomly selected to participate in the study in hope that it would provide a more representative sampling of the community.
“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. Wesley Tait Stevens with Riverside University Health System, one of the study’s co-authors.
The survey was conducted across two weekends at the beginning of July — when Riverside County saw its highest numbers of new infections per day since the pandemic began, reaching a peak of 1,431 on July 10.
The county has been adding an average of 757 new cases per day over the past week. The overall COVID-19 death toll has reached 671, with 50 of the fatalities confirmed within the last week.