RALEIGH, N.C. — Duke University has told thousands of patients whose surgical instruments were mistakenly washed in hydraulic fluid that there is no risk of getting infections as a result.

The university hospital system, however, did not address patients' fears that the mistake led to an increased risk of autoimmune or other noninfectious disorders.

In a

letter sent this week

to nearly 4,000 patients, the university cited a risk study done by an outside researcher it hired.

"We regret when any patient suffers," Duke said, adding that there is "always some risk of an undesirable outcome in any procedure."

Patients affected, however, say the health system was slow to respond and is evasive in its reaction. They see this latest letter as nothing more than fancy wording with very little relative substance.

As one of the 3,800 patients caught up in the issue, Carol Svec said she is less than pleased with Duke's recent response.

"It has been my impression that they've been very casual about this and hoping that it would go away," Svec said.

In the letter, Duke states "patients have not been put at risk," but Svec said the statement is not true.

"We were not at risk for bacterial infection, but we don't know what else we were put at risk for," she said.

Duke is focusing on infection in the letter, stating the tools were sterile and that infection rates did not increase. Bacteria-free, however, does not mean chemical-free, Svec said, and she wants to know how the chemicals will affect her body.

Duke officials said the chemical analysis is still to come.

Svec also said that she feels the letter leaves patients with a false impression.

"What worries me is that some patients will take this and put it in a box and not worry, when in fact the worst worries are yet to come," Svec said.

For two months late last year, surgeons at Duke Health Raleigh Hospital and Durham Regional Hospital unknowingly used instruments that had been washed with hydraulic fluid instead of soap.

The error happened after elevator workers drained hydraulic fluid into empty soap containers without changing the labels.

The federal Centers for Medicare and Medicaid Services issued a report last week saying the hospitals had put patients in "immediate jeopardy" by not detecting the problem, despite complaints from medical staff about slick tools.