Health officials in Washington are warning that the coronavirus is spreading more widely throughout the state, an increase likely driven by transmissions that took place over Memorial Day weekend.

In a report issued Saturday, the Washington State Department of Health pointed to two distinct hot spots, both of which are showing worrying signs of increased spreading.

Confirmed COVID-19 cases are rising fastest in four counties east of the Cascade Mountains, mostly rural and agricultural areas that were spared from the first substantial outbreak in Washington.

Both cases and the rate at which tests are coming back positive are increasing in Yakima, Spokane, Franklin and Benton counties. Projections in three of those counties show they are at risk of recording hundreds of new cases a day by the end of the month; Yakima County is already recording cases at that rapid rate.

The outbreaks east of the Cascades are now comparable to the worst days of the coronavirus epidemic in King County, home to Seattle, in mid-March. Though they are much more sparsely populated, there are as many cases per capita now in the eastern counties as there were in Seattle during the height of its outbreak.

King County has a population 2.25 million and has recorded 8,611 coronavirus cases, according to state health department figures, or a little under four cases per 1,000 residents. Yakima County, population 250,000, has recorded 5,129 confirmed cases, a per capita ratio five times higher than King County.

The state health department also said it was concerned about a growing number of cases confirmed in western Washington. Models maintained by epidemiologists at the University of Washington show the estimated reproductive threshold — the average number of people someone infected with the virus infects — rising above the 1.0 threshold needed to keep cases on the decline.

Washington, the state that suffered the first confirmed coronavirus case back in January, is now beginning to reopen its economy. In a statement Saturday, Gov. Jay Inslee (D) said the new report was cause for concern.

“The report estimates cases and deaths will soon increase substantially if COVID-19 continues to spread at current levels,” Inslee said. “This data will force us to look for some creative solutions and strengthen our strong local – state partnerships to address the disease activity.”

He asked Washingtonians to wear masks more vigilantly and to continue practicing social distancing.

“This is not the time to give up on efforts to protect ourselves, our families and our communities. We are still in the middle of a pandemic that is continuing to infect and kill Washingtonians,” Inslee said.

In a statement, Kathy Lofy, Washington state’s health officer, said the increased number of cases was likely a result of Memorial Day weekend festivities about three weeks ago. That stretch of time would give people a sufficient period in which to get sick, develop symptoms and progress to a state in which they seek treatment for their illness.

Lofy said the new cases are not indicative of any spread at protests over the murder of George Floyd, an unarmed black man who was killed by police in Minneapolis. The protests that have been especially large in Seattle, Tacoma and other western Washington towns.

Any new cases among protesters probably have not had time to manifest in substantial ways yet and likely would not show up for at least another week.

After about a month at a stable plateau, the number of confirmed coronavirus cases across the country has started to rise. More than 20,000 new cases have been identified on each of the last four days, according to the COVID Tracking Project. Doctors confirmed nearly 24,000 cases on Thursday and more than 26,000 cases on Friday.

States that raced to reopen their economies, such as Texas, Florida, Arizona and the Carolinas, are seeing substantial increases. But so too are states such as Washington, where restrictions have been lifted more slowly.

More than 2,066,000 people in the United States have been diagnosed with the coronavirus. More than 115,000 have died, by far the highest total of any country in the world.