(Reuters) – Connecticut said on Friday that two patients who recently underwent surgery at a VA Hospital may have been exposed to a rare brain disease, adding to 13 people already reported at risk in Massachusetts and New Hampshire.

The potential for exposure is believed to be the result of doctors using the same surgical instruments on several different patients. Those instruments were initially used on a New Hampshire patient, who has since died. That patient is now believed to have had a sporadic form of Creutzfeldt-Jakob disease, a condition similar to “mad cow” disease but not linked to beef consumption.

Not every operating room keeps such specialty instruments on hand, and they can end up in different states if they’ve been leased from medical supply companies.

Health officials have said that the normal cleaning procedures for surgical instruments used at hospitals reduce, but do not eradicate, the microscopic protein that causes CJD.

“On 8-29, 2013, the New Hampshire Department of Health notified the Connecticut Department of Public Health that two patients treated at the VA Hospital in West Haven may have been exposed to Creutzfeldt-Jakob disease,” William Gerrish, a spokesman for the Connecticut Department of Public Health, said in an email to Reuters.

“The risk of transmission of CJD to the two patients at the VA is considered very low. The general public and any other patients at the VA Hospital and their employees are not at any risk,” he said.

A New Hampshire health department spokeswoman, Kris Neilsen, said earlier on Friday that a fourth state may also be investigating possible exposure to patients, but she declined to name that state.

The Centers for Disease Control said in an emailed statement that it was in contact with the state health department in New Hampshire and the hospital to evaluate the situation. An official at the Food and Drug Administration was not immediately available.

A spokeswoman for medical supply company Medtronic Inc confirmed that its instruments were used in some of the cases, but not all.

The scare began after a neurosurgery patient at a hospital in Manchester, New Hampshire, died recently bearing symptoms of Sporadic CJD.

An autopsy to determine if CJD was present in the patient is being conducted, with results expected in about four weeks, said Neilsen, the New Hampshire health department spokeswoman.

There is no treatment or screening test for the disease, which has symptoms including failing memory, personality changes, blindness and sudden jerky movements. It normally kills in a matter of months.

Officials in Massachusetts and New Hampshire said all 15 patients who may have been exposed there have been notified.

(Additional reporting by Julie Steenhuysen in Chicago; editing by Daniel Trotta and Matthew Lewis)