A mother had a cotton swab left inside her after having a baby at Middlemore Hospital, and another patient died because extremely low blood sugar levels weren't picked up.
The number of "serious adverse events" at Counties Manukau Health facilities has almost doubled since the last Health and Quality and Safety Commission report in 2012.
The health board had 45 incidents in the year to June 2013. The previous report listed 24.
Included in the 45 are cases of patients who have been diagnosed with cancer after waiting long periods to be seen by a specialist.
One patient had a chest x-ray that was not examined properly and cancer was found seven months later.
Thirty-three of the 45 events related to falls.
Three patients died as a result of their falls, five suffered cerebral haemorrhages and 10 fractured hips.
The board is now working to reduce the risk of serious harm from falls by introducing a fall prevention programme.
It plans to hand out non-slip socks, nurse patients on low beds and put up falls alert signs to help reduce accidents.
Almost 500 serious adverse events happened in New Zealand hospitals in the year.
Of the 489 events, 437 were reported by district health boards. That was 21 per cent higher than the 360 reported a year earlier.
Commission chairman professor Alan Merry says much of the increase is likely due to improved reporting.
That was expected to continue in coming years as systems improved further.
- Manukau Courier
Are our classrooms becoming overcrowded?