A spokesperson added: “We have been assured the health board is taking all precautionary measures to prevent incidents like this from happening again.”
Llais, which represents people across health and social care in Wales, said the public needed to know processes to protect them were being followed and working.
People, it said, would be understandably worried unsterilised instruments were used, and patients waited to be told.
A spokesperson said: “Health boards have a duty to keep people safe and, in line with the duty of candour, to be open and take prompt action when things go wrong.”
They added: “It’s essential for trust and confidence that the investigation is thorough and that learning leads to real change.”
Plaid Cymru dubbed the failings “terrifying”.
It said: “Those responsible for such glaring failings on clinical safety should be brought to account – and the health board must show full transparency on how it is dealing with this.”
The Welsh Conservative’s health spokesman Peter Fox called it “a serious breach of care.”
“An apology alone is not good enough. We need a full investigation into why this appalling incident occurred.”
Reform’s Laura Anne Jones, said: “It’s scandalous that it’s taken three weeks for my constituents to be informed.”
The Welsh Liberal Democrats and the Green Party have been approached for comment.