Up to 15% of Multnomah County residents who have tested positive for COVID-19 shared no contacts with the county, Dr. Jennifer Vines, county health officer, said Aug. 3.

That's a problem for public health officials trying to trace contacts with infected people.

"That could genuinely be because they've taken precautions and they don't have contacts," Vines said, "or it could be because they declined to talk to public health."

But health officials have struggled to trace cases. For the week ending July 25, 54% of Multnomah County's COVID-19 cases could not be traced to another case, far short of the benchmarks set by state officials to reopen counties.