A county health clinic in northwestern Arkansas was evacuated Thursday after more than two dozen employees became ill.

Arkansas Department of Health spokeswoman Ann Wright says no patients at the Washington County Health Department were among those sickened. The cause of the illness was under investigation, but local television station KHBS reported that the sickness was caused by pesticides.

The sick employees complained of dizziness and nausea, Wright said. The Washington County Regional Medical Center released a statement saying it had received 26 people suffering from nausea and vomiting.

The hospital said the sick employees had been exposed to an “unconfirmed source” while at the health department.

John Gibson, county administrator, told KHBS that three people were taken to a hospital in Springdale. None of the illnesses was considered life-threatening, Gibson said.

Gibson said a pest-control company had sprayed insecticide in the building three days ago.

Rick Johnson, health department administrator, said the outbreak moved among the staff too quickly to have been a flu or other communicable illness.

“There’s definitely an external factor at work here,” Johnson said.