Incidents such as one in Hawke's Bay in which unsterilised equipment was used on patients should not happen, Health Minister David Clark says.

Hawke's Bay District Health Board has launched an investigation after a batch of 91 pieces of equipment sent out to Hawke's Bay Hospital theatres, outpatient clinics and by district nurses between February 2 and 11 did not undergo final sterilisation.

Half of the equipment was used. Up to 55 people from across Hawke's Bay including children and elderly patients are affected and will now require testing for infections such as HIV and hepatitis. It will be 24 weeks before they are in the clear.

DHB chief executive Kevin Snee told a press conference this morning that while the equipment was cleaned and heated to a very high temperature, the final stage of sterilisation was not carried out.

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"This means there is a very remote chance those patients may have been exposed to an infection," he said.

The DHB became aware of the issue on Monday when a theatre nurse noticed the colour coding on the packet was wrong and notified a manager.

Snee apologised for any distress patients were suffering.

"Understandably we're seeking answers about how this failure occurred."

Clark told reporters this afternoon it was too early to say what had gone wrong.

"This kind of thing shouldn't happen," he said.

He also ruled out considering compensation for affected people at this stage.

"It's too soon to say. We don't know exactly what's happened in this situation yet. That will need a fuller investigation," he said.

Clark said such incidents were rare.