ap photo Housing and Urban Development Secretary Ben Carson, left, talks with resident Maggie Rawland, right, after touring the Plymouth Place senior housing facility with Iowa Gov. Kim Reynolds, Tuesday in Des Moines.

DES MOINES — Health officials in Iowa are working to determine what is causing a spike in coronavirus cases in the northwest corner of the state where several counties are seeing a surge, Gov. Kim Reynolds said Tuesday.

Sioux County has a 14-day positivity rate of 30 percent. Public health officials usually recommend mitigation measures including crowd restrictions, face coverings and business closures to slow the virus’ spread when an area surpasses 5 percent positivity.

Two adjacent counties — Lyon and Osceola — have rates above 20 percent

“In Sioux County there isn’t a specific outbreak so we need to continue doing the case investigation. I think that it’s saying that there is significant community spread happening within the county and then they need to do what they can to help mitigate that,” Reynolds said.

The Republican governor acknowledged the rate of spread is very high but said she’s hopeful it is stabilizing. The county began seeing cases increase in early August when and has since seen the 14-day rolling total of positive cases increase six-fold since.

“I don’t know what’s going on up there,” Reynolds said. “It’s what we see a lot of times when we start to open things up and I think we should expect that you’re going to see probably a little uptick in cases.”

The White House coronavirus task force had been advising Iowa to implement a mask policy for weeks as the state surged to the top of all states for virus spread in August. Reynolds has resisted. She closed bars in six counties for a short time when increases were noticed in highly populated areas and in university towns. In the past few weeks, the overall state situation has improved, but daily statistics remain elevated.

Iowa’s positive case numbers surpassed 81,000 on Tuesday as the state posted 517 new cases in the past 24 hours and 19 deaths, raising the death toll to 1,285.

“It’s obvious that people are not wearing masks in northwest Iowa,” said David Johnson, a retired state senator who lives in Ocheyedan in Osceola County.

He said funerals and weddings are packed with people not wearing masks or social distancing. In his city, typically only those working in businesses where masks are required, such as a clinic or pharmacy, wear them, he said.