More than 50 patients at Hawke's Bay Hospital may have had inadequately sterilised surgical tools used on them, the DHB has admitted.
Ninety-one pieces of equipment failed to go through the final stage of sterilisation earlier this month.
The equipment was used on 55 patients between February 2 and 11.
DHB Chief Executive Kevin Snee admitted that an error had been made during sterilisation.
"While this batch of equipment was properly cleaned, heated to a very high temperature and dried, the final sterilisation process was not completed as it should have been."
Bacterial infection has been ruled out due to the other two stages of sterilisation, however there is a low risk of viral infection.
Dr Snee said an investigation had been opened into the incident.
"Understandably the DHB is seeking answers as to how this failure occurred and we have launched an investigation to understand how this happened. This investigation will also be externally reviewed."
Patients who are at risk of contracting illnesses through the equipment have been notified.
The DHB has reassured patients that their chance of contracting any infection is minimal.
"We would like to reassure the public of the expert scientific advice we have received to emphasise how small the risk of infection is."
Dr Snee also apologised to anyone affected by the incident.
"The DHB unreservedly apologises for any distress this has caused and we will be working closely with those affected."
Any patients with concerns are urged to contact Hawke's Bay Hospital.