Alberta Health Services has issued a warning after thousands of patients had their confidential health information "inappropriately accessed" by a former AHS employee.

An AHS investigation has determined that the former employee accessed the health information of 1,309 Albertans. The same former employee viewed the "demographic information" of another 11,539 individuals, AHS said in a news release Monday.

AHS said the former employee accessed the electronic files on the AHS Netcare and Netcare Personal Directory programs between January 2004 and July 2015.

Despite the breach, health officials say none of the medical files have been altered or compromised.

"The protection of patient privacy is not only a legislated duty of our employees, it's part of our patient-first culture, and our values," AHS interim vice-president Dr. Francois Belanger said in the news release.

"We take privacy incidents very seriously, and continue to work with our employees to ensure they're supported with privacy education and regular communication."

AHS said it began auditing the worker after receiving a complaint from another AHS employee.

The matter was also reported to Alberta Health and to the Office of the Information and Privacy Commissioner of Alberta.

Patients are being notified via direct-mailed letters which are going out Monday.

Patients affected by the breach can expect to receive their notifications within five to seven business days.

The letters will also include information on how patients can request a full audit log of all the activity on their files.

AHS has set up a call-in line to support people affected by the breach. Information about the call-in line is included in the letters.