The ACT Integrity Commission is considering more than 365,000 emails in its investigation into alleged privacy breaches from staff at Dhulwa Mental Health Unit.
It only took three weeks for the commission to decide to investigate the matter after receiving a report, the commission's annual report revealed.
This turnaround was much quicker than the average time it took for the commission to assess complaints, which was 74 days for reports received last year.
The commission is investigating the breaches as an alleged "misuse of official information".
The investigation was one of two the commission started in the 2022-23 year.
The commission did not reveal what the other investigation, dubbed Operation Athena, was related to.
The alleged breaches were revealed in March in an all-staff email sent by Canberra Health Services chief executive Dave Peffer.
Mr Peffer told staff there were 13 patients affected by the breach which had occurred "over a period of years". He said records had been "deliberately emailed" to people outside the organisation.
"In recent weeks we've discovered a serious breach in the privacy of patient health records within one of our teams, extending back some time," Mr Peffer said.
"Records have been sent by a small number of team members to multiple team members to multiple people within one of our industrial partners.
"Records that should never have been shared outside the organisation, without the express consent of our patients."
Canberra Health Services and Minister for Mental Health Emma Davidson dodged questions on the matter when it was first made public but released information over a series of days.
The privacy breaches were allegedly committed by staff at Dhulwa who had sent information to the Australian Nursing and Midwifery Federation.
Several staff were stood down over the matter and one person, mental health nurse Carol Sandland, was sacked.
Ms Sandland is suing Canberra Health Services, saying she was unfairly dismissed from her job at the unit.
A Fair Work Commission hearing earlier this year heard Ms Sandland had sent emails to the nurses' union including patients' names, details about their medication and plans for a person to be admitted, among other confidential information.
The ANMF has previously argued the disclosures were lawful as it related to safety concerns. The union said it had a long standing relationship with Canberra Health Services around the lawful disclosure of personal information when nurses and midwives and specific concerns around patient safety.
The annual report also revealed the commission received 148 reports of corruption over the year. Of these, 120 were corruption complaints, 22 were mandatory corruption notifications and six disclosures of disclosable conduct.
