A total of 13 patients from an N.H hospital and other states who underwent brain surgery may have possibly been exposed to a rare and deadly disease through contaminated equipment, said state health officials on Wednesday.

According to USA Today, eight of them were from the New Hampshire hospital while the rest affected were from other states with a rare and fatal brain disease called Creutzfeldt - Jakob disease (CJD), which seems similar to “mad cow” disease. Those two diseases, however, are not related.

Health officials affirmed that the risk of infection was “extremely low.” They are also sure that the patient who underwent brain surgery in May and died in August at the Catholic Medical Center in Concord, N.H., had sporadic CJD, which spontaneously occurs idiopathic, meaning, no known cause. The National Prion Disease Pathology Surveillance Center is currently doing autopsies to confirm this belief.

Other patients may have been infected afterwards via surgical equipment improperly sterilized. The abnormal protein – the disease-causing prion – cannot be terminated in the usual hospital sterilization. Some surgical instruments used were just rented, and the equipment has been quarantined.

José Montero, the director of public health at the New Hampshire Department of Health and Human Service told USA Today "The risk to these individuals is considered extremely low, 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."

Conversely, there is no noted risk to other patients admitted in the Concord Hospital, their staff or to the public.

CJD infects just one out of one million people globally and there are roughly 200 people diagnosed yearly in the United States. CJD is often confused with “mad cow” disease or bovine spongiform encephalopathy, a brain-wasting prion disease passed on from infected cattle.