Officially, Riverside County has more than 35,000 known cases of COVID-19 since the start of the pandemic.
But a study by the Riverside University Health System finds far more people are likely to have been infected with the virus without having been tested or diagnosed.
The study, conducted over two weekends this month, tested 1,726 individuals, finding 101 had antibodies for COVID-19. That is a positivity rate of 5.9%.
If that positivity rate is extrapolated to Riverside County's entire population, it would mean about 118,000 to 175,400 people in the county had been infected.
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While some of those infected individuals may not have experienced negative effects from the virus, health officials note those without symptoms can still spread it to others, who may face more serious consequences.
The presence of antibodies indicates the individual has at some point been infected by the virus and the body's immune system has fought it off. Antibodies stay in the blood even after the virus is gone from the body. Health experts remain uncertain as to how long the antibodies remain in the body and continue to provide protection against future infections.
"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."
In addition to the known 35,000 cases, Riverside County has had 671 deaths from COVID-19 and currently has 488 people hospitalized. Health officials say more than 356,000 people have been tested for the virus.