A child battling legionnaires disease is believed to have been exposed to the potentially deadly bacteria during a stay at Starship Children's Hospital.
The child is in intensive care and other patients in the ward have been tested for the disease, which is a form of pneumonia.
Director of child health Dr Richard Aickin is reassuring parents and staff that it is an isolated incident.
"The safety of our patients is always our highest priority and I want to make it clear there is no reason for the public to be alarmed.
Patients at the the hospital had tested negative for the disease.
"The patients we have tested have weakened immune systems, making them susceptible to Legionella, so we believe it is very unlikely any other people are affected."
Legionella is usually caught through infected water or soil. Tests were being carried out in the children's ward to determine the source of the disease, Auckland District Health Board spokesman Matt Rogers said.
Aickin said the incubation period has passed without any new cases emerging.
"We are confident this is an isolated occurrence."
This is the first case of Legionnaires disease acquired by a patient at Starship or Auckland City Hospital.
The hospital would not release any further details of the affected patient.
One person died and eight were hospitalised after an outbreak of legionnaires disease in Canterbury in November.
The affected patients were believed to be infected while working in their gardens.
- Auckland Now