Seattle area COVID-19 tests show infections declining

For all those living in the Seattle region hunkering down in their homes, there is new evidence that social distancing is reversing coronavirus infection rates, a green shoot of hope in this frightening spring of 2020.

After analyzing results of more than 25,000 nasal swab tests taken in hospital emergency rooms and daytime clinics in the greater Seattle area, researchers have found compelling evidence that COVID-19 infections in the heart of Washington state’s outbreak peaked roughly on March 28 and are now in steady decline.

At that apparent apex of infections, about 13% of those tests taken outside of hospitals were coming back positive. If that downward trend — and rigorous physical distancing — continues, researchers predict that by mid-May as few as 2% of tests in the region will be positive.

“This is the first objective data that suggests the incidence of infection appears to be decreasing here,” said Dr. Larry Corey, past president and director of Fred Hutchinson Cancer Research Center, a professor in its Vaccine and Infectious Disease Division and an author of the unpublished study.

“It’s gratifying to see that the sacrifices people are making are having results,” he said. “I want to thank the people of this region, the governor and the mayor for how they have responded to this crisis.”

Corey said the researchers have submitted their findings in a letter to an academic journal, but felt the data are of major interest to the general public and should be shared as quickly as possible.

The work is a collaboration among teams led by Dr. Keith Jerome, a professor at both Fred Hutch and the University of Washington who directs the UW Virology Lab; and Dr. Alex Greninger, assistant professor at UW’s Department of Laboratory Medicine. The analysis was done by a Fred Hutch statistical team led by Drs. April Randhawa, Leigh Fisher, Shuying Li and Jessica Andriesen.

The researchers collected data from tests involving 25,486 individuals, mostly in King and Snohomish counties who were treated as outpatients — those visiting various clinics but not hospitalized. A smaller contingent tested had visited emergency rooms in the same region. Thus, the researchers had data on patient demographics and site-of-origin data for the samples.

As a way to track the epidemic, Hutch-based statisticians evaluated the rate of positive COVID-19 patients coming to these clinics each day. The study began on March 2, the first day that regional SARS-CoV-2 detection was initiated in the UW Virology Lab, and it tracked the rate of positivity until April 8.

“We reasoned that the analysis of the rate of COVID positivity in outpatient and ER facilities with established connections to the laboratory would allow estimates of COVID-19 incidence in our region,” Corey said.