Health officials said equipment used during the Cape Cod surgeries was also used on a New Hampshire patient believed to have Creutzfeldt Jakob disease - a degenerative brain disorder spread by infected brain tissue and cerebrospinal fluid.
Eight New Hampshire neurosurgery patients have also been contacted about a possible exposure, according to the New Hampshire Department of Health and Human Services.
"The risk to these individuals is considered extremely low," Dr. José Montero, the department's director of public health, said in a statement. "But after extensive expert discussion, we could not conclude that there was no risk, so we are taking the step of notifying the patients and providing them with as much information as we can. Our sympathies are with all of the patients and their families, as this may be a confusing and difficult situation."
Creutzfeldt Jakob disease, or CJD, is extremely rare, affecting one in a million people worldwide per year, according to the National Institutes of Health. It's believed to be caused by abnormal proteins called prions that lead to a sponge-like pattern of holes in the brain. It can be diagnosed only through an autopsy.
Most CJD cases are sporadic, meaning they arise in people with no known risk factors. But up to 10 percent of cases are hereditary, according to the NIH, and 1 percent of them are acquired through contact with contaminated brain tissue.
"The risk of contracting CJD from a surgical instrument is extremely low," the Massachusetts Department of Public Health said in its statement. "There have been only four confirmed cases in the world, and none of these cases occurred in the U.S."
Early symptoms of the disease include memory loss, behavioral changes, lack of coordination and visual disturbances, which give way to involuntary movements, blindness, weakness and coma. There's no cure, and about 90 percent of patients die within a year, according to the NIH.
The surgical equipment used on the suspected CJD patient and 13 others in New Hampshire and Massachusetts was made by Medtronic, a company that makes tools for neurosurgery. The Massachusetts Department of Public Health is working with Medtronic to "determine the extent of potential exposure" in the Cape Cod patients, according to the statement.
"The five patients have been notified and counseled, and there is no risk to hospital staff or members of the public," the department said in a statement.