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A mystery virus at a Central North Island prison has confined 50 inmates to their cells.
The virus swept through Tongariro/ Rangipo Prison near Turangi on Friday and prompted prison authorities to issue a "lockdown" for three days.
The move has angered inmates and members of their families who were stopped from seeing each other during scheduled visits at the weekend.
A Department for Corrections spokesman said the prison was closed to visitors to maintain public health and to ensure the virus didn't spread.
However, the sister of one prisoner told the Daily Post guards were free to come and go during the weekend, making attempts by corrections officials to contain the virus futile.
The woman, who did not want to be identified, said she had saved money for several weeks to make the trip from Auckland to see her brother at the weekend.
No one told her the prison was closed until her brother rang from prison on Friday afternoon, after she had already arrived in Taupo.
"I wasn't sure what was going on so I drove to Turangi but they wouldn't let me through the gate."
She said a friend, who was also planning to visit a prisoner, was contacted on Friday at 10pm by corrections department staff, informing her the prison was off-limits to the public for three days.
The woman said the lockdown had inconvenienced dozens of people who had come from around the North Island to visit family or friends behind bars.
Her brother told her unwell prisoners had been confined to their cells over the weekend and were "playing up".
"No one's very happy about the whole thing," she said.
More than 50 inmates have been affected by the virus, which caused diarrhoea and high temperatures.
By last night, only eight prisoners were still being cared for by the prison's on-call nurse.
Officials are unclear what caused the virus but stress it is not food poisoning.
A preliminary report indicates the cause is not salmonella and officials are waiting on the results of further tests which were due today.
"We are awaiting test results before we can determine how it was contracted and whether it is related to any viral illness in the community," said Gavin Dalziel, the corrections department's regional manager for Central/ Waikato.
One staff member displayed symptoms and was sent to their own health professional. However, it is unclear if the staff member's symptoms were linked to the same virus at the prison.
Mr Dalziel has defended the department's actions in closing the prison to the public.
"We decided to take an isolation precaution in the interests of overall public health.
"At that stage we had not received the results from the laboratory so exercised caution in that respect," he said.
"Once it was established we had a potential infectious situation on our hands we advised as many of the visitors as possible.
"As you can appreciate this took time and some people would have been advised later than others."
