A Health Canada recall of toys and novelty sets containing small, powerful magnets significantly reduced the number of emergency room visits by kids who had swallowed them, according to a new Toronto study.

The 2013 recall alert warned parents that the magnets used in sets often marketed as "adult toys" could easily be inhaled or swallowed by children, causing serious health problems. Health Canada followed that up with its first-ever mandatory consumer product recall, after one company failed to comply with the voluntary recall.

In 2011 and 2012, the two years before the recall, there were 22 cases of multiple magnet ingestions at Toronto’s Hospital for Sick Children (SickKids). Those cases resulted in six operations and nine endoscopies or similar procedures used to examine the esophagus, stomach and colon.

But in the two years after the recall, there were only five cases of multiple magnet ingestions, according to the study published Friday in the Journal of Pediatrics. Only one child required an operation and four required scopes.

"The recall worked, just by the pure numbers that we saw," Dr. Daniel Rosenfield, a SickKids emergency room physician who led the study, told CTVNews.ca in a telephone interview.

"We had a significantly smaller number of children presenting to our emergency department with swallowed magnets, multiple magnets specifically."

SickKids says previous research by Dr. Rosenfield and his colleagues was "instrumental" in getting Health Canada to issue a mandatory recall on the magnet sets, typically used for puzzle work, sculpture building or mental stimulation.

In 2011, Dr. Rosenfield and two other doctors published a case study involving a three-year-old boy who required laparoscopy to remove three magnets that had stuck together in his intestine. They later published a study that warned of "a significant increase of magnetic foreign body injuries."

"Kids can swallow lots of things and unless they get stuck, they’ll come out normally," Dr. Rosenfield told CTVNews.ca. "The problem with the magnets is, if you swallowed one and then had another five minutes later and another five minutes after that, they can get stuck across different loops in your gut and then pull them together."

Health Canada says that the swallowed magnets can attract one another while moving through the bowel, causing the intestines to twist, creating blockages and life-threatening perforations of intestinal walls.

"For survivors, there can be serious lifelong health problems," the agency said.

"I think this is a good case where Health Canada used its power correctly when we identified a threat…and was able to protect children’s health that way," Dr. Rosenfield said, noting that media coverage of the magnet dangers also helped increase awareness.

Dr. Rosenfield said his latest study highlights the importance of product recalls and should serve as a reminder that products containing the dangerous magnets are still out there. People can buy the magnetic sets online, either through websites such as Kijiji or from manufacturers outside of Canada.

"Parents and doctors and everyone else still need to remain vigilant," he said. "These products still exist and they’re still coming into our emergency departments or to our clinics, despite the fact that there’s been a lot of education around the dangers and the recalls."