Five surgeries started at Dunedin Hospital before medical staff realised their instruments were not properly sterilised and the patients involved were not informed of the breach.
The breaches include surgical cement, hair and a water-filled connector being found on or within the instruments or their tray once procedures started.
The Southern District Health Board (SDHB) confirmed the breaches, and said there was no documentation that the breaches had been openly disclosed to the patients involved.
SDHB chief executive Chris Fleming said in the first four cases, the contaminated material or instrument were removed and replaced before being used on the patient.
"The Southern DHB Sterile Services Team sterilises an average number of 150,000 packs of surgical equipment per year, and we take these five identified breaches extremely seriously," he said.
"This work is particularly challenging for the Sterile Services team in Dunedin, who work in a cramped space that is not fit for purpose.
"There is a risk that even if the instruments have not been used directly on a patient, they may have come into contact with other instruments that had been used, thereby compromising the sterile status of the other equipment."
He said the contaminants had been through the sterilisation process and the risk of them containing any infectious material was extremely low.
There were no adverse outcomes to the patients as a result of these breaches, Fleming said.
"Our practice is to advise patients of the events that breach our standards, including when the material has not touched the patient or the instrument not used on the patient. However it appear this has not happened in these cases."
RNZ has sought an interview with Fleming and asked for further information about whether the patients involved have still not been informed.
"We want to acknowledge their hard work in difficult circumstances, and can advise that a new facility is being developed in Dunedin, which is expected to be completed next year," Fleming said.
"In the interim, significant work has been undertaken to tighten processes and monitoring to mitigate the risks created by the facility constraints. This includes additional staffing, including a dedicated education and quality resource, and implementing additional steps to ensure greater checking and monitoring."
The breaches were reviewed and opportunities for improvement were identified, he said.
"We acknowledge that any event is too many and we continue to focus on improving our processes and thank our teams for their efforts in this."