Sonoma County using antibody tests to help determine scope of coronavirus outbreak
After three months into the local fight against the new coronavirus, it still remains unclear how many Sonoma County residents actually have been infected by the contagion since only a sliver of the county’s nearly 500,000 people have been tested.
In fact, just 32,000 people, or 6% of the population, know for sure if they’ve had or still have the virus because they tested positive. Since the county mounted an aggressive, multifacted testing regimen beginning in April, more and more cases have emerged but the area’s total infection rate continues to hover at only 2% of those tested.
With the COVID-19 outbreak under control at least for now, county public health officials are turning their attention to trying to discern how many residents were infected by the virus, yet didn’t likely know it because their bodies fought it off. To get a clearer picture of the magnitude of the virus spread, county health officials last week started antibody testing approved by the U.S. Food and Drug Administration. These tests detect often unknown previous coronavirus infections, and the results will help guide the next stage of public health response to the ongoing battle against the highly contagious pathogen in the community. And the test results could possibly point to the need for more public health precautions, said Dr. Sundari Mase, the county’s health officer.
“If (for example) 5% of our community is already infected, we’d tell people we didn’t know that this extra huge number of people got infected so be careful, wear your facial coverings, really observe the mitigation measures,” Mase said in an interview this week.
What’s more, Dr. Lee Riley, professor of infectious diseases and vaccinology at UC Berkeley School of Public Health, said if the epidemic continues and a second wave of infections occurs in a community, local health officials can evaluate whether people who have the antibodies showing previous infections are less likely to get infected or develop symptoms during such a spike or surge.
Antibodies are proteins that help fight off infections. But it’s not clear yet if having antibodies to the coronavirus can protect someone from becoming reinfected with the infectious disease or how long that antibody protection may last for an individual.
County health officials are prioritizing the tests for COVID-19 antibodies in individuals that are part of high-risk groups, such as first responders, those who previously tested positive for the coronavirus and the people they’ve come in close contact with. Infected residents are being tested to determine if they in fact developed antibodies in their bloodstream, while their contacts are being tested to see if any previously were misdiagnosed negative for the infectious disease that has swept the globe, killing at least 113,000 people in the United States, nearly 4,900 in California and four residents of Sonoma County.
If the antibody test results point to a far higher prevalence of infection in the county than previously thought, public health workers could begin testing the general population, Mase said.
It’s not prudent to conduct widespread antibody testing among the general public now, she said, because it could be that the “true percentage” of county residents who actually have contracted the virus could be less than 1%. When that real prevalence, the share of residents in a community infected by the coronavirus, is less than 1%, the antibody testing can result in a number of false positives or false negatives, the county health officer said.
Meanwhile, Vitalant, operator of the area’s major blood donation center, also has begun conducting COVID-19 antibody tests on everybody who donates blood. It take two weeks for donors to get the results.
The new testing at the blood bank, which began June 1, is aimed at letting blood donors know whether their immune system has produced antibodies to fight the coronavirus, though that does not mean someone is definitely immune to it. Such donors also could be eligible to donate so-called “convalescent plasma,” an experimental therapy that could help people recover from severe cases of COVID-19.
Unlike the county’s ongoing diagnostic testing confirming people have the virus, this test only detects antibodies that point to a previous viral infection. And the test reveals if the immune system indeed has responded to defeat the infection.
Mase said antibody testing could be used to retest individuals who previously were given diagnostic tests through the county’s contact tracing program because they were in close contact with someone infected with COVID-19. Some of these individuals could have tested negative earlier, because they were tested before the virus could be detected in their bodies.
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