HILLSBORO, Ore. (AP) -- Authorities say six employees from Intel's Hillsboro campus were taken to a hospital for mysterious respiratory issues for the second time in less than a week.

The Oregonian/OregonLive reports Intel said Monday morning the employees were being treated for minor breathing difficulty.

Officials said 16 other people were treated Monday, but were not taken to the hospital.

Fifteen employees went to hospitals Thursday complaining of difficulty breathing. The employees reported "respiratory irritation" and "minor breathing difficulty," according to Intel. All of them were home from the hospital by late Friday.

Intel said previous and current investigations have shown no hazardous materials were released.

Intel says it evacuated people from the affected building.

Intel's Ronler Acres campus is the company's most advanced manufacturing facility, where the company develops each new generation of microprocessor.