Nearly 150 patients who underwent weight-loss surgery in Montreal have been told they may have been exposed to HIV, hepatitis or other infections from an improperly cleaned medical instrument, according to CTV News.

Patients who underwent bariatric surgery between 2012 and 2014 at the Lachine Hospital in Montreal's west end learned of the problem earlier this year. They were told that a review of sterilization protocols found that a tool used during the surgery hadn't been thoroughly cleaned.

The tool, called a liver retractor, is typically disassembled, physically cleaned and then sterilized. But the review found that the device was not properly disassembled before being cleaned, although it was sterilized.

“We realized by unscrewing it completely that there was some sort of ashe and debris remaining in the internal part of the instrument,” said Charles Frenette, the director of infection prevention at McGill University Health Centre.

Not knowing what that debris was or whether it was contaminated, the hospital decided to alert the affected patients.

Frenette told CTV Montreal Tuesday that the risk of infection is “really, really minimal.”

Nevertheless, 147 bariatric surgery patients have been contacted and told to undergo blood tests.

So far, 90 percent of the patients have been tested and all have come back negative. But the hospital has been unable to contact about 15 affected patients, and is still looking for them.

Read more: