DURHAM, N.C. — Six months after a medical mix-up at two of its hospitals, Duke University Health Systems is taking additional steps to address patients' concerns.

On Monday, the health care giant was scheduled to send out a second letter to nearly 4,000 of its patients who were operated on with tainted surgical tools.

Duke's latest letter updates patients on its investigation into the matter and informs them of a newly created center staffed with environmental health experts to consult with patients worried about the mix-up.

Cheryl Whitfield, one of approximately 3,800 patients affected, believes Duke's actions are a little too late.

More than six months after surgery to repair her shattered elbow, Whitfield's arm is visibly swollen. She said she fears that the hydraulic fluid that was mistakenly used to clean surgical instruments may be responsible for her symptoms. She said, however, that she is not sure.

Duke said contracted workers put hydraulic fluid into vats that was then mistakenly used to clean surgical tools at two Duke-affiliated hospitals.

Lab analysis on the hydraulic fluid is not expected back for a few more weeks.

Duke University Health CEO Dr. Victor Dzau recently told WRAL that the slow response many patients have complained about was because he had wanted to wait until Duke got the lab analysis back.

Dzau also said that he would like to monitor the patients involved to see if there are any long-term effects from the hydraulic fluid.

Duke is expected to release more details Tuesday regarding the consultation center.