Sampling suggests infection rate of 3.4 percent

Jeff Bethel, a researcher with the TRACE-COVID-19 study and associate professor at the Oregon State University College of Public Health and Human Sciences, goes over instructions with project volunteers outside the Guin Library at the Hatfield Marine Science Center on June 20. (Photos courtesy Oregon State University)

NEWPORT — Random sampling of Newport residents the weekend before last — the latest iteration of Oregon State University’s Team-based Rapid Assessment of Community-level Coronavirus Epidemics study, which models the prevalence of COVID-19 in communities — indicates that about 34 out of every 1,000 people in the city were then infected with the virus.

On June 20 and 21, 30 two-person field teams of volunteers canvassed 30 neighborhoods after meeting at the Hatfield Marine Science Center to collect field kits and receive marching orders. The largely local field teams boarded 30 white OSU Extension transport vans shortly after 10 a.m. on Saturday and Sunday, and visited 336 households, where 569 people agreed to self-administer tests. Thirteen of those people tested positive for SARS-CoV-2, the virus that causes COVID-19.

Jeff Bethel, a member of the TRACE leadership team and an associate professor in OSU’s College of Public Health and Human Sciences, expressed gratitude to the 71 percent of visited households that agreed to contribute samples to the study. “The high participation rate gives us confidence that our findings are robust and a good indication of how widespread the virus causing COVID-19 is in the general population of Newport,” Bethel said.

TRACE began in Corvallis and was later expanded to Bend. Results from the first three weekends of sampling in Benton County indicated that between one and two of every 1,000 Corvallis residents had the virus — 20 to 30 times lower than the apparent local prevalence.

The Newport project is the first time TRACE has sought to gauge community-wide spread in the midst of an outbreak — it was undertaken two weeks following the announcement that 124 workers at Pacific Seafood tested positive. It’s not a picture of all of those who have ever been infected but an epidemiological point in time, modeling how many people’s bodies contained the virus’s RNA on those two days in June.

The first three weekends of sampling in Corvallis were all prior to the reopening of restaurants and businesses under phase one. Results are still pending for samples taken there June 13 and 14, which could illuminate if and how increased social and economic activity influenced infections rates. The study in Bend was undertaken the last two days of May, two weeks after Benton County entered phase one, and indicated an infection rate of one in 1,000.

Prevalence is modeled by combining the results of the two days of random sampling with previous data about positive cases from the local health department and Oregon Heath Authority. The latest weekly report from the health authority, published on June 24, listed 246 cases in the Newport 97365 ZIP code, just under 2.3 percent of the population or almost 23 out of every 1,000 residents. That was already the highest number of infections per capita in Oregon. The next highest was in the 97026 ZIP code, on the north side of the Salem metro area, with 13 cases per 1,000.

“The tally of cases already reported by health officials tells us how many people are known to be sick with COVID-19,” Bethel said. “This number is well understood to underestimate the actual number of infected individuals because it misses asymptomatic individuals and people who have not sought testing or do not have access to testing. In contrast, the TRACE estimate of prevalence tells us about the fraction of individuals in Newport who are infected — whether or not they have symptoms, and whether or not they have access to testing. Public health and elected officials need this kind of information to plan and deploy resources.”

It might be noted that a fairly high number of those testing positive since the outbreak in Newport were reported to be asymptomatic, but those were tested because of close contact with a known positive case or another factor that made testing accessible.

Ben Dalziel, assistant professor in the College of Science at OSU and co-director of the project, said the results indicate “the potential for significant further spread unless strong actions are taken to reverse the course of COVID-19 in Newport.”

Kaety Jacobson, chair of the Lincoln County Board of Commissioners, said, “This kind of random sampling gives us a type of data we don’t have, and we will be working with OHA and OSU to understand how to incorporate this into the data tools we currently use. We will also be looking at the feasibility and cost of doing further sampling studies like this one.”

The TRACE study is a collaboration of the OSU colleges of Science, Agricultural Sciences, Engineering, Public Health and Human Sciences, and the Carlson College of Veterinary Medicine, in partnership with county health officials.


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