Some 66 patients, most of them children, are being recalled for blood tests by the Health Service Executive (HSE) after a dentist who treated them tested positive for HIV.
The patients' families, all in the Dublin region, received notification of the recall this week but this only came to light yesterday.
The HSE said the dentist worked in two locations in the region, but would not identify them.
The dentist was diagnosed with HIV last October after feeling unwell. The HSE said it immediately made sure the dentist had no further contact with patients.
Asked why it was only now contacting patients treated by the dentist, some nine months later, the HSE's director of public health, Dr Brian O'Herlihy, said it took some time to identify the patients who should be contacted.
Only patients who would have had open wounds in their mouths as a result of treatment by the dentist were being recalled for blood tests.
Dr O'Herlihy said there were national guidelines in place on how to deal with situations which arose when a healthcare worker was diagnosed with a blood-borne infection.