WHITBY, Ont. - Ontario's privacy commissioner has launched an investigation after the health information of more than 83,000 people who attended flu clinics in Durham Region, east of Toronto, disappeared.

The privacy commission office was advised Monday by the Durham Region health department that a USB key containing the records had gone missing, said spokesman Bob Spence.

The device contained the names, addresses, phone numbers, dates of birth and health card numbers of patients who attended H1N1 flu vaccination clinics in the region between Oct. 23 and Dec. 15.

The focus of the investigation will be on what happened, how it happened and what steps can be taken to prevent a similar incident from occurring in the future, said Spence.

The probe will work in co-operation with, but be separate from Durham Region's own probe, he added.

"The privacy commission is always concerned any time that personal information is inadvertently disclosed or lost,"said Spence.

"This is personal health information that is very sensitive. You don't want your neighbour to know what type of operations and so on you've had."

Durham health officials said the USB key was lost on Durham Region headquarters property in Whitby while being taken to a clinic.

Health Department officials have searched but haven't found it, but said there's no reason to believe the device was deliberately taken.

They added the ability to read the personal health information is limited.

Spence said Durham officials responded very quickly to this.

"There have been times in the past where internal investigations or searches have gone on for a couple of months and the public hasn't been notified," said Spence.

Durham Region said it "sincerely apologizes for this lapse in protection and safekeeping of personal health information."

It said a letter will be sent out to the patients affected and anyone with concerns or questions can contact Durham Health at 905-666-6241 or 1-800-841-2729.