There is at least one case of tuberculosis, known as TB, in the Spring Hill prison in North Waikato.
Spring Hill Prison director Megan Tuhoro said the secure and controlled nature of the prison environment meant they were able to quickly isolate the unwell prisoner.
She said they were following the advice of Waikato District Health Board's Public Health Service, and there was no risk to any other prisoners or staff at this stage.
The prisoner arrived into prison on August 31, during Covid-19 alert level 2 restrictions.
Tuhoro said all newly received prisoners were managed together in a separation unit for their first 14 days in custody, and all prison staff wore masks while working in this unit.
Tuberculosis is an infectious bacterial disease which can become serious. People can have the disease with no symptoms, and can carry it for some time before they become symptomatic. It generally affects the lungs, but can also affect other parts of the body.
The World Health Organisation said the level of TB in prisons has been reported to be up to 100 times higher than that of the civilian population.
It believes cases of TB in prisons may account for up to 25 per cent of a country's burden of TB.
Corrections says the prisoner had an initial health assessment on September 1 with no respiratory symptoms raised or observed.
On September 18 he was seen by health services and raised concerns about symptoms he was experiencing, and was taken to hospital.
He returned on September 28 and is being cared for in a single cell in a separation unit, and all staff working with him are wearing PPE.
Tuhoro said a health and safety review is underway.
She said the prisoner's condition was stable.
The case was initially announced by the Corrections Association. The Waikato DHB has been approached for comment.
The Corrections department have a joint management plan with the Ministry of Health to manage TB outbreaks in prisons.
The Ministry of Health's website says there are typically about 300 cases of TB diagnosed in the country each year, and New Zealand is classified as a low incidence country for the disease.