The 20 serious and sentinel events reported in the year to June included a patient death which followed an incorrect diagnosis in the emergency department and two women burned by heat pads while in labour.
The report listed the death of an in-patient because of an overdose of non-prescribed drugs, an intrauterine death still being investigated and four suicides.
To the end of June last year, seven serious medical mistakes were reported.
There were three in 2007, which was the first year information about serious and sentinel events was made public.
Chief medical officer Richard Bunton said a national reporting system, with definite criteria of what district health boards should and should not be reporting, had been developed.
Improving the reporting of serious events would bring overall benefits for patients, he said.
Nationally, there were 308 serious incidents.
Of those, 92 died during admission or shortly afterwards, although not necessarily as a result of the event.
Each year, about 950,000 people are admitted to public hospitals.
The report showed about three in 10,000 were affected by a serious incident.
The Ministry of Health's quality improvement committee, which released the report, expected the number of serious events reported nationally would continue to rise during the next few years.
Among the events in Otago, a patient came to the emergency department with hip pain and was seen in the middle of a busy shift.
A normal X-ray, good response to simple pain relief and the ability to move led to a diagnosis of a sprain injury.
However, the patient came back to the department two days later unconscious and septicaemic.
An abscess in muscle deep in the abdomen was diagnosed and despite surgery and intensive care, the patient died.
If a blood test had been ordered at the first presentation, the condition could have been diagnosed earlier, which might have made a difference, Mr Bunton said.
Another patient in the ISIS rehabilitation ward at Wakari Hospital died from an overdose, after acquiring methadone prescribed for someone else.
The most likely source of the methadone was another patient, but this could not be verified.
Two women were burned by heat pads during labour.
One of them required dressings to burn wounds on her thighs and stomach.
Another woman was bleeding for two hours and lost 1.5 litres of blood after birth before the self-employed midwife informed the obstetric team.
During this time no observations of vital signs were made and no blood tests were sent for cross match.
The woman needed two units of red blood cells.
Action taken after the incident included education sessions for core and self-employed midwives and medical staff, with open discussion of issues in recent cases, and the undertaking of skills and scenario-based activities.
Team-building exercises were incorporated into education activities to promote the importance of team aspects of caring for women in the maternity ward.
It was also recommended fracture sites be identified with an arrow drawn in permanent marker on the patient's leg after a patient had a medical procedure done on the wrong leg.
The patient had also indicated the wrong leg to the house surgeon.
Falls represented 27% of the serious events reported nationally.
In Otago, three patients suffered fractures and one a head injury after falling.
Intensive care specialist and principal medical adviser to the ministry, Dr David Galler said all deaths and injuries were a tragedy for families and of great concern for district health boards.
"However, the reality is that even with the best people, processes and systems, errors can occur.
"When they do, we need to find out what went wrong, whether it could have been prevented and what improvements or changes should be made."
A sentinel event is one which is life-threatening or has led to an unanticipated death or major loss of function, and a serious event is one which requires significant additional treatment.
