Auckland District Health Board is confident it can contain an instance of tuberculosis which has forced it to test hundreds of staff and patients.
The DHB is testing 240 staff and up to 20 patients after a woman died from a rare form of the disease.
The woman was in hospital for several weeks before the disease was diagnosed.
Chief medical officer David Sage said 240 staff, including some medical students, have been linked to the woman. However, the number of patients is less than 20.
He said the woman's case was not diagnosed because she had a very unusual response to a rare form of the disease - so the usual signs of TB were not present.
Dr Sage said TB is a slow and insidious disease which becomes infectious only in its respiratory form, so anyone who had been exposed or infected at this time would not be in any danger.
While there are up to 400 cases of tuberculosis a year in New Zealand, Dr Sage said it is unusual to die from it.