Her office "will investigate the matter and ensure that the personal health information of Ontarians is not being compromised by any organizations under my jurisdiction," Information and Privacy Commissioner Ann Cavoukian said in an email to Ontario's New Democrats, who requested her help.
Cavoukian added that she's already contacted the Health Ministry to confirm that no personal health details are being provided to U.S. border services.
NDP provincial health critic France Gelinas said she's been contacted by three people who have been denied entry to the U.S. based on their personal health history.
One woman she spoke to, Ellen Richardson, has gone public with her story, saying she was turned away Monday at Toronto's Pearson airport by a U.S. customs agent because she was hospitalized in June 2012 for clinical depression.
Richardson attempted suicide in 2001 by jumping off a bridge, which left her a paraplegic. But her mental health has improved with medication and professional help from a psychiatrist, she said.
She said she travelled through the United States several times in recent years and never had a problem.
This time, the agent cited the U.S. Immigration and Nationality Act, which denies entry to people who have had a physical or mental disorder that may pose a "threat to the property, safety or welfare" of themselves or others, she said.
"It's ridiculous. It's utterly ridiculous," she said.
"I was never a threat to others. I would never harm anyone."
Richardson, who takes medication to combat depression, said she provided the U.S. agent with the name and phone number of her psychiatrist, but it wasn't enough.
She was told she would have to get "medical clearance" and be examined by one of only three doctors in Toronto whose assessments are accepted by Homeland Security, she said.
Richardson, who has a website and wrote a book about her struggle with depression, said she has no recollection of police being involved in her 2012 hospitalization.
She said she had become suicidal, wrote a suicide note and called her mother, who came over and called 911.
"I wasn't a threat to anyone, other than myself," Richardson said.
Gelinas said another person she spoke to told her that they had been turned away at the border over a physical ailment that had nothing to do with mental health.
She wouldn't provide any details to protect the person's privacy, but Gelinas said she was told that the U.S. agent in that case also mentioned a fairly recent, specific medical episode that happened in an Ontario hospital.
Gelinas said at first she tried to find some explanation for why U.S. authorities might have the information, such as police records. She asked many questions, but nothing seemed to explain how the Department of Homeland Security got the information.
"The amount of their personal information that is spit back at them is astonishing," she said.
"I have no idea how this could happen, but it did. I believe those people. They have given me physical, tangible proof that this happened."
A person's medical history must remain confidential, she said. To hear that specific details of a person's medical history is being shared with a foreign government is "extremely alarming."
Health Minister Deb Matthews owes Ontarians an explanation, Gelinas added.
U.S. authorities don't have access to medical or other health records for Ontarians travelling to the United States, said Samantha Grant, a spokeswoman for Matthews.
Government officials referred all other questions to police services, saying it was an operational matter.
Federal law allows personal information to be transferred outside Canada, even without the consent of the individual to whom the information relates. Once the information is in foreign hands, the laws of that country will apply.
Canada's privacy commissioner has called for the federal government to re-examine the circumstances under which it allows personal information about Canadians to be processed outside Canada.
Mike Sullivan, the New Democrat MP who represents the Toronto riding where Richardson lives, says he has sent a letter to the federal privacy commissioner's office asking for an investigation into the matter.
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