Officials at Hawke's Bay District Health Board say 55 patients may be affected by equipment that was not properly sterilised.
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Hawke's Bay DHB chief executive Kevin Snee said they were made aware of the situation on Monday when one of the nurses alerted the line manager.
The batch of equipment was used in Hawke's Bay hospital operating theatres and sent out to outpatient clinics where it was used by district nurses between 2 and 11 February.
Mr Snee said the formal sterilisation process was not completed as it should have been.
"The risk of infection is extremely remote," he said.
"I want to apologise for any distress this has caused any patients.
"We take responsibility for the problem. My priority as a doctor is patient care. This has never happened before and it won't happen again."
Executive director for provider services Colin Hutchison said a batch of equipment that should have been sterilised overnight between the 1 and 2 February "failed to undergo the third and final stage of cleaning of our surgical equipment which is the sterilisation process".
On 2 February that equipment was then distributed. There were 91 pieces of equipment. Half of the equipment was recalled before it was used.
About 55 potential patients who may have had this equipment used were identified. Of those, 18 patients were within the main theatre block.
Packs were sent to health facilities across Hawke's Bay.
In the last day, the DHB said it had taken a lot of advice nationally and locally to understand the clinical risk for these patients who may have had this equipment used on them and the advice was that the risk to patients was minimal, but it was not zero.
Hawke's Bay DHB medical officer of health, Dr Nick Jones, said the advice they received was that "despite there being very low risk, we can't be 100 percent certain that the risk is zero because of the failure of the final step".
"We will be providing vaccination as appropriate."
The possibility of blood-borne viruses - hepatitis B, hepatitis C and HIV - remain a concern.
"Of those three, our greatest concern would be hepatitis B," he said.
However, patients won't know for 24 weeks if they have been affected.