On Thursday night, Oregon Gov. Kate Brown issued a stay-home order for Umatilla County, the first time she has sent a county back into lockdown after reopening businesses from COVID-19.

This morning, one reason became clear: An Oregon State University door-to-door canvass suggests 17% of the county's largest city, Hermiston, has COVID.

The OSU public health study teams canvassed 471 people in Hermiston last weekend. Forty-one of them tested positive for SARS-CoV-2, the virus that causes COVID-19. University researchers estimate that 169 of every 1,000 people in Hermiston have the virus, or 3,000 people total.

"Our results indicate the virus is extremely widespread in Hermiston and more prevalent than previous data had indicated," said Ben Dalziel, an OSU assistant science professor and co-director of the project. "Half of the 30 randomly selected neighborhoods we visited had at least one positive participant. This means that the virus is very widespread within the community, not clustered in only a few locations."

OSU researchers also took samples from the sewers of Hermiston and Boardman, where they found "consistently strong viral signals in both cities that have remained very high and not decreased over time," said Tyler Radniecki of the OSU College of Engineering.

Perhaps most disconcerting: The study found 80% of the Hermiston residents who tested positive had no symptoms. That suggests the virus could be spreading among city residents to the most vulnerable people.

The OSU study, called Team-based Rapid Assessment of Community-level coronavirus Epidemics, or TRACE, began this spring in Corvallis and later expanded to Bend and Newport. The university sent researchers to Hermiston after the Eastern Oregon city became an epicenter of the virus's spread.

Hermiston is an Oregon agricultural hub, famous for its watermelon crop. Four of the state's 12 largest active workplace outbreaks occurred at warehouses in the city: at Lamb Weston, a frozen potato packing plant; Medelez Trucking; Shearer's Foods, which packages potato chips and other snacks; and a Walmart Distribution Center.

Gov. Brown issued a statement on the study's findings. "This study confirms what we have feared based on weeks of troubling data from the Oregon Health Authority: The coronavirus has spread throughout Hermiston and threatens the entire community," she wrote. "Umatilla County is now in a 'baseline, stay home' status and we must do everything possible to contain these outbreaks."

The governor's office tells WW that Brown reviewed the OSU data before issuing her order to reclose the county.

Spokesman Charles Boyle says the governor's Thursday briefing "included a preliminary briefing on the OSU TRACE study and wastewater samples in Hermiston that added more data points to the trends we were seeing in climbing case rates and community spread."