Duke University Health System has settled claims by patients who alleged they suffered health problems after being exposed to hydraulic fluid on surgical instruments at two Duke hospitals in 2004.

The News & Observer of Raleigh reported Wednesday that the confidential settlement resolved claims against Duke by an unknown number of clients.

Meanwhile, dozens of patients exposed to the hydraulic fluid at Durham Regional and Duke Raleigh hospitals have sued the companies that contracted with Duke to sterilize the equipment.

The lawsuit said the plaintiffs were patients of Durham Regional or Duke Raleigh hospitals in late 2004, when more than 3,600 patients were operated on with instruments mistakenly cleaned with used hydraulic fluid. The fluid had been drained from an elevator and sent back to the hospitals for use as detergent.