COVID-19 Positivity Rates in Multnomah County Have Been Rising for Months

Test positivity rates are a useful shorthand for COVID’s spread in a community.

13.8%.

That’s the percentage of COVID-19 tests that came back positive in Multnomah County in the week ending June 25. It’s the highest positivity rate in Oregon’s most populous county since the week ending Feb. 5. And it’s one of several indications that a significant amount of COVID is being transmitted in Portland as the pandemic’s third summer begins.

U.S. Centers for Disease Control and Prevention data officially shows that community transmission is “high” in nine counties. That means the state recommends indoor masking there.

Test positivity rates are a useful shorthand for COVID’s spread in a community because they indicate when tests are not showing all the cases that are erupting.

In past phases of the pandemic, Oregon public health officials said a 5% positivity rate was the mark they were shooting for. To be sure, rapid tests have become more available, which may mean tons of tests are happening that aren’t reported to public health officials; it may also mean some people are getting professionally tested after knowing they’re positive.

“We know this is an undercount because more people are testing at home,” says Oregon Health Authority spokesman Rudy Owens. “Recent evidence from a study this spring in New York City suggests about 1 in 30 cases were being reported to public health.”

And from the end of February through the beginning of April, the average weekly positivity rate fell below 5%; it’s mostly been climbing since.

“Trends tell us people are still getting sick, and we know the virus is circulating widely in Oregon,” Owens says.

Here’s how positivity rates have increased in Multnomah County since May 1.

Week beginning Test positivity

May 1 10.1%

May 8 10.9%

May 15 11.8%

May 22 12.5%

May 29 12.4%

June 5 12.2%

June 12 12.6%

June 19 14.7%

Source: Oregon Health Authority