Nearly 500 instances of Canterbury health professionals accessing patient medical records have been reviewed since the country's first online health database was launched, but all were found to be legitimate queries.

The Canterbury District Health Board (CDHB) rolled out the pioneering HealthOne system (previously called the electronic Shared Care Record View) in September 2013, and it was expanded to the West Coast DHB area in November 2014.

The system allows thousands of health professionals - including GPs, pharmacists and hospital clinicians - access to the medical records of almost 550,000 enrolled patients across Canterbury and the West Coast.

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CDHB chief medical officer Dr Nigel Millar said 479 "accesses" to patient medical records had been reviewed since the launch, but all were found to be legitimate queries and none had required disciplinary action to be taken against staff.

Millar said the cases did not represent instances of inappropriate access, but were "simply accesses we were unable to validate automatically". The 479 reviewed cases represented less than one in a thousand accesses, he said.

The number of flagged cases rose steadily in the initial months after the system went live and peaked during winter 2014 "perhaps because during the winter people are more likely to seek healthcare somewhere other than where they are registered".

Flagged cases had since dropped to a "noticeably lower level", despite overall use of the system continuing to grow.

Millar said flags could be raised whenever a clinician accessed a patient's records at a primary care facility other than where the patient was enrolled, or if the patient was not enrolled anywhere.

"Having access to HealthOne for clinicians working at multiple facilities and often in after hours, acute and emergency settings provides a significant benefit to patients, especially those requiring urgent care."

In September, Privacy Commissioner John Edwards expressed concerns about inappropriate access to patient records by health workers and about online security in general following high-profile hacking incidents like that of Apple's iCloud in August, where hundreds of private photographs of celebrities were stolen.

"If that sort of sophisticated hacking was brought to bear on these systems, it would be horrific," he said.

Labour health spokeswoman Annette King asked the Government in January to investigate privacy issues relating to the sharing of records between GPs and hospitals, but said its response was a "deaf ear".

"I do think the sharing of health information between health professionals is important for patients to ensure joined up diagnosis, treatment options ... but the weakness has always been not adequately engaging the people themselves," she said.

"Many of those I have spoken to have no idea their information has been shared. Informed consent and explanation must be the first principle."

Millar said every access to HealthOne was audited and reports were generated regularly to review any potential "indicators" or red flags.

"Where the indicator can't be validated using the data available, contact will be made with the user," he said.

"Where there is no new evidence provided to support the access and there is a potential privacy breach or non-compliance, access to HealthOne is removed. Appropriate action is then taken by the clinician's employer and/or the clinician's registering body."

To date, 878 people from Canterbury and the West Coast have opted off HealthOne.

Patients can opt out of having part or all of their information shared electronically by talking to their GP or phoning 0508 testsafe (0508 837 872).