At least four patients have been exposed to unsterilised surgical equipment during operations at facilities run by the Southern, Waikato and Canterbury District Health Boards.
At Southern DHB, old congealed blood was discovered inside a surgical screw driver that was used during an operation, and in a second incident, equipment was exposed to air when it should not have been because it was incorrectly put together.
Southern DHB Chief Medical Officer Nigel Miller said the blood would have been through a sterilisation process but it's still not good enough.
"It doesn't seem right, I wouldn't like that to happen. It's an uncomfortable thought.
"The process of cleaning, the decontamination - that wasn't done to the highest possible standard."
The affected patients were not notified by the DHB.
"On both occasions we got a detailed risk analysis from the people with the most experience in infectious diseases, and we decided there wasn't any risk to the patients and therefore we didn't inform them," Dr Miller said.
Newshub requested details under the Official Information Act about equipment sterilisation at all 20 DHBs after the Hawke's Bay Hospital sterilisation scare in February, when more than 50 patients may have had inadequately sterilised surgical tools used on them. Fifty-five patients are now facing 24 weeks of HIV and hepatitis testing.
Thirteen of the 20 DHBs reported incidents, including Hawke's Bay, but in the vast majority of cases the problems were identified before the tools were used.
Two weeks after being contacted, Waikato DHB failed to get back to Newshub. It subsequently reported eight incidents related to sterilisation, four of which appear to have exposed patients to unsterilised equipment and in other cases forced delays to operations which were already underway.
In one case at Waikato Hospital last year, a surgeon noted during an operation there was a stiffness when attempting to drill into the bone - and when he removed the drill he noticed tissue from a previous operation was still inside.
Other cases noted dried blood and bone residue stuck on equipment.
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In February at Canterbury DHB, two unsterilised surgical telescopes were used on two patients during operations after an old sterilising machine malfunctioned and didn't complete its cycle.
Chief Medical Officer Sue Nightingale told Newshub it's unacceptable.
"We've had a system in place since our last sterilisation incident in 2006 to ensure we can't have incidents that get through the system without being sterilised.
"At the end of the cycle there is a printout that tells you if the cycle's successful or not. It did say the cycle was not successful, it failed, but that got missed and the instruments got sent along to theatre. Unfortunately in theatre that wasn't picked up straight away."
Dr Nightingale says patients were told after it was picked up later that day. The reassurance was made by the next day no harm was done to the patients.
"At the time we checked every batch that went through the steriliser in the preceding month to make sure no other failures had been missed - there were none. We checked every sterilisation pack in the entire district health board including all of our peripheral hospitals that day."
Following the incident, a serious event investigation was launched and is still underway. It's looking at the processes, the sterile services unit and the processes in theatre. Extra steps have also been taken to stop any future events.
"We've instituted a third check, so in the sterilisation unit before instruments leave they're checked by another person who isn't involved in the process of sterilising them.
Dr Nightingale says extra training and reminders are available for staff.
"When we move into our new hospital the Hagley Hospital in November, we've got a fully automated system coming online - so it could just not happen again when that system's in place."
Unanswered questions surround Waikato DHB data. The DHB delayed its information release to Newshub by two weeks despite repeated requests for the data. The information provided is inconclusive and clarification will be asked of the DHB.
Southern DHB says both incidents at its hospitals were immediately responded to and an infectious disease specialist/infection prevention and control risk assessment was made. The patients were monitored postoperatively for 30 days and checked at 90 days. No infection or adverse outcome was found.
Dr Miller says they were isolated incidents considering there were around 350,000 sterilisations in 2018/19, and processes have not been changed since.
"I don't think we've changed any steps, but people have been made aware in the process and we keep up the awareness of everyone in the system.
"Our staff are really committed to this, they take pride in their work, they don't cut corners, they really want to do it to the best of their ability."
No one lost their jobs at Canterbury DHB or Southern DHB following the incidents. Waikato DHB has been approached for comment.