Door-to-door tests help track COVID-19’s spread in one Oregon town

Surveying neighborhoods directly may give a more accurate view than other methods

Testing in Corvallis, Oregon

On April 20, a member of a coronavirus testing team in Corvallis, Ore., demonstrates a carefully choreographed protocol, one that keeps distance between study volunteers and researchers.

Karl Maasdam

Through mid-May, researchers will be knocking on doors in Corvallis, Ore., and asking people inside their homes if they’d agree to a coronavirus test. These door-to-door tests, which began on April 19, may be the first of their kind in the country, the scientists say, and will help determine whether people currently have the virus that causes COVID-19. The tests promise to provide an accurate estimate of infection rates in the college town of about 60,000 people.

Preliminary results suggest that approximately 2 in 1,000 people in Corvallis had SARS-CoV-2, the virus that causes COVID-19, when they were tested over the weekend of April 25 and 26, researchers report May 7. That rate is lower than estimates from some other places in the United States and globally, and lower than at other time points during the pandemic, but still high enough to be concerned about, the team says.   

The weekends of testing involve asking families to swab their noses and put the samples into a container on the doorstep, while researchers wait outside at a safe distance. Science News spoke with population biologist Benjamin Dalziel at Oregon State University, one of the researchers leading the study, called TRACE-COVID-19. This interview has been edited for brevity and clarity.

SN: What can random door-to-door sampling tell us that other methods, like drive-up tents, can’t?

Dalziel: The door-to-door piece is very important. Embedded into the case counts that we get from other projects are barriers to health care, which are numerous and include the ability to access a tent [or] the types of people who will click on a Facebook ad to get mailed a test. That’s a biased sample.

The truly representative sample of a community that’s obtained by going door to door is one of the key values of this study. By randomly sampling a large number of individuals — our target is 960 a weekend — you get that representative sample. Each team goes to a single neighborhood, and works that neighborhood for two days. If someone isn’t home, there’s a chance to go back the next day.

This is also an opportunity to engage with the community. We leave behind informational material. There are other benefits than just reducing barriers to access.

SN: How quickly was the project put together?

Dalziel: It was four to six weeks of feverish problem solving.… We felt like we were assembling an airplane in midair.

SN: How do you pick the houses?

Dalziel: The first stage is we select neighborhoods. Thirty neighborhoods is our current number, and we’re shooting for somewhere between eight and 16 households in each one. It depends on how many people are home.

Each team goes to a neighborhood, and selects households at random by starting in a particular place and going to every 5th or 6th or 8th house, walking in a certain pattern. A simple example is always turning right.

SN: How are people reacting?

Dalziel: It is extraordinary. The response is overwhelmingly positive. Most folks knew who we were and wanted to participate. For instance, when we first went out, within two minutes of parking, somebody cruised by, rolled down the window, and said, “Hey, you’re those TRACE people! Thank you so much. Can you come to my house?”

SN: How do your early results compare with others, such as Seattle SCAN’s, which uses tests by mail?

Dalziel:  Our results are similar to those from the Seattle SCAN study for April 16 to April 21.… Our estimate of approximately 2 infected people out of 1,000 is lower than some other places and times, and we can be grateful for that.

But it is still high enough to be concerning. If we relaxed social distancing too quickly, this prevalence would be sufficient to initiate a second phase of exponential growth in the epidemic.

SN: The study is designed to last about a month. What comes next?

Dalziel: We’re working to incorporate antibody [testing] as fast as we can. As the news indicates, the antibody question has some complexities to it…. Our current funding is for a four-week, first phase study. We’re actively looking at a number of ways to scale up.

Laura Sanders is the neuroscience writer. She holds a Ph.D. in molecular biology from the University of Southern California.

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