DURHAM, N.C. — An outside research firm will monitor the health of patients affected in a hydraulic fluid mix-up at two Duke University Health System-affiliated hospitals, the hospital system announced Thursday.

PharmaLink, based in Research Triangle Park, will collect and analyze health information from patients who may have been exposed last fall to surgical instruments that were mistakenly washed in used hydraulic fluid during the cleaning process.

Duke Health's program will detect any unusual patterns or symptoms and illnesses among affected patients.

PharmaLink is a full-service clinical research organization that has managed similar programs involving up to 250,000 patients. Over the next year PharmaLink researchers will periodically report back to Duke Health about its findings.

"It's the right thing to do, it's what patients asked for," said Dr. Michael Cuffe, Duke Health's vice-president of medical affairs. "We've been very responsive. Using an outside group is the next step."

Duke Health has said that the residual amount of hydraulic fluid left on the tools was less than a fraction of a drop and that the risk of infection was low and the tools were still sterile. Officials admit, however, that long-term effects of exposure are unknown.

"If we do find some sort of impact on human health, we will let patients know directly. We will let them know immediately," Cuffe said.

One year since the mix-up, however, some patients affected feel the mistake is the source of their mysterious health problems.

"I was supposed to be better in four to six weeks," said Bambi Giltz, who has surgery Dec. 20 at Duke Health Raleigh Hospital.

Glitz said persistent bruising and swelling have not gone away and that her doctors are unable to explain why.

"I've been able to walk," she said. "It's just really painful. Not a day goes by that I'm not in severe pain."

With Duke Health's new study, Glitz, and patients like her who are now seeing other doctors, will have to have their medical records sent to PharmaLink. Patient records already in the Duke Health system, however, will transfer into the study.

Lawyers for affected patients have claimed that patients exposed to the surgical instruments are at a higher risk than Duke Health experts want to admit. In their own independent analyses, researchers said they found more metals in the fluid than what Duke reported.