How many people have been infected with COVID-19 in King County? Who is more likely to be infected and how severe are their symptoms? And are there common risk factors we can identify among people who became infected so we can reduce risk?

Public health officials are hunting for answers to these questions and more with a new study. About 5,000 randomly selected households from across King County will be receiving postcards in early August 2020 from Public Health – Seattle & King County, asking them to volunteer to have a few drops of blood taken from a finger. This is known as a seroprevalence study (“sero” referring to the blood).

Their blood will be analyzed for the presence of antibodies to the virus the causes COVID-19. An antibody test is different from a test that tells someone if they are currently infected with COVID-19.

Participants will also answer a confidential questionnaire that will help understand the spread and severity of disease. Taken together, information from the study will ultimately help to save lives.

“We don’t know the full extent of people infected with COVID-19 locally because many have mild symptoms or none at all,” said Dr. Jeff Duchin, Health Officer for Public Health – Seattle & King County. “This study is designed to give us a better understanding of COVID-19 transmission spread, which will inform our response efforts to slow the spread of disease in our community.”

How the antibody testing will work

In the first phase of the study, about 5000 households will receive postcard invitations to participate. They will visit a website and answer some initial screening questions. Only about 800 households can be tested, so not everyone who receives a postcard will be selected. The aim is for participants to reflect the diversity of King County, as well as groups that have had more illnesses and financial impacts from COVID-19.

For households that are selected, one representative will answer a few additional questions about people in the household and schedule an appointment to either go to a testing site or for a mobile testing team to come to their neighborhood. The Public Health study team will follow up with each participating household member to complete their own survey, asking about their recent activities, and if they have had symptoms of COVID-19.

When participating household members go to get tested, Public Health staffers will make a small pinprick on a participant’s finger, just enough for a few drops of blood. Testing will run through mid-August 2020.

In the study’s second phase, Public Health will be conducting targeted outreach to communities of color to invite their participation. This will provide additional information specifically about communities burdened with the most disproportionate impact from COVID-19, due to the cumulative practices and institutional systems of racism.

What the results will tell us

For the community, this study will shed more light on several important questions about COVID-19 infections, including:

• The extent of people infected in King County, including those with mild or no symptoms
• Why people chose not to get tested if they did have symptoms
• How many mild cases of COVID were never tested and detected
• If there are patterns in risk factors for infection

This information is important in directing strategy and resources to where they are needed most, which can help to slow spread of COVID-19 and save lives. Public Health plans to have preliminary results by September.

Each participant will also receive their results. A positive test means that they were infected with COVID-19. A positive test may also mean there is some ability to fight off future infections from COVID-19, but it is not known with certainty if there is protection or how long it might last.

There is also a possibility that someone with a positive antibody test could get infected with COVID-19 again. And if someone tests negative for antibodies, there is a chance that they could have had COVID-19 previously, even if the test does not find antibodies at the time of testing.

Other studies

King County’s seroprevalence study is one of several working to increase understanding of the spread of COVID-19 around the state and country.

UW Medicine, in partnership with the Paul G. Allen Family Foundation and the Washington State Department of Health, is launching a statewide seroprevalence study this summer, which will include some participants from King County.

Washington is also one of seven states in which some households will receive a kit to collect a blood sample at home and send it to a lab to be tested for antibody against the coronavirus that causes COVID-19. A national study will follow a similar process for a study of people in all states.

The current Public Health – Seattle & King County study is funded by the Centers for Disease Control and Prevention (CDC). If additional funding becomes available, new rounds of testing could help to understand local changes in infections and risk factors over time.