The Centers for Disease Control and Prevention published a study Friday identifying coronavirus antibodies in 1% of Oregonians whose blood was tested this spring.
The study, conducted by the Oregon Health Authority, found nine out of 897 people tested from May 11 to June 15 had antibodies to coronavirus – indicating a previously undetected infection.
The Oregon findings underscore what public health officials have already said: Only a fraction of active infections are identified through diagnostic tests. But it is difficult to draw sweeping conclusions from the relatively small number of anti-antibody cases identified in the study.
“The data suggest that a substantial number of COVID-19 cases in Oregon have gone undiagnosed and have not been reported and that a large portion of Oregon’s population remains susceptible to COVID-19 infection,” state officials wrote in the study, published as part of a weekly report by the Centers for Disease Control and Prevention.
Unlike diagnostic tests that identify active infections, serology tests analyze blood to determine if someone has been previously infected by identifying the presence of antibodies. It can often take two to three weeks after an infection for someone to develop those antibodies.
Dr. Paul Cieslak, one of the authors, said the results were “pretty close to what we expected.” He warned that with only nine identified antibody cases in the study, “there is a margin of error that this will be very valuable,” with a range of .2% to 1.8%.
“We do not want to make this more than it was,” he said. “But it confirmed what we thought, that there were a bunch of undiagnosed infections.”
The Oregon study provides some support for modeling that officials have been using for months to analyze prevalence during the pandemic. The modeling last month, for example, estimated 52,400 Oregonians infected on July 2 – even though only one-fifth of these were identified through diagnostic tests.
Findings from the antibody study, if extrapolated to the entire population of the state, would equate to about 42,000 infections by June 15th.
“I do not think our results are terribly inconsistent with the modeling, let me say that,” Cieslak said.
The latest Oregon modeling estimates 88,800 cumulative infections as of July 30, again with only about one in five identified through diagnostic tests.
To complete the antibody study, officials recruited 19 facilities in Oregon to supply blood samples from patients to the state Public Health Laboratory for testing. They found that older Oregonians were more likely to have antibodies screened among them.
The test did not identify any antibodies in 29 children tested and found only two people with antibodies among 485 adults 64 and younger.
But among Oregonians 65 and older, seven people out of 383 had antibodies tested.
The state launched its study in May one week after telling The Oregonian / OregonLive that it did not analyze the results of antibody tests it did not receive from labs to estimate the prevalence of infections. With so many dubious antibody tests on the market, government officials said they did not trust the results.
But Cieslak said the state tempered those concerns by conducting the in-house research lab with a serology test that selected it.
State officials have said more antibody studies are planned, including in long-term facilities and schools. Cieslak said he is not sure when that could happen.
The state’s findings are generally consistent with estimates by federal officials that only about one in 10 infections has been identified through diagnostic tests since the beginning of the pandemic. Officials in Boise, meanwhile, have completed a similar antibody study that tested previous infections in 1.79% of people.
As of Friday, the state has confirmed 22,613 confirmed presumed infections from diagnostic tests. Except for the new study, Oregon does not report any antibody test results.
“We are here for the time being,” Cieslak said, noting that millions of Oregonians are not infected with coronavirus. “We need to keep the social distance until we get very good treatments as a reliable vaccine.”
– Brad Schmidt; [email protected]; 503-294-7628; @_brad_schmidt
Subscribe to Oregonian / OregonLive newsletters en podcasts for the latest news and top stories.
