A Waikato prison is grappling with a mass illness that started on Christmas Eve

One Spring Hill Corrections Facility prisoner has a confirmed case of campylobacter, while a total of 47 inmates are unwell.

Acting Prison Director Megan Tuhoro said they are working closely with the Waikato District Health Board's Public Health Service to establish what's made the prisoners sick.

She says all prison meals are prepared in supervised industrial kitchens.

Tuhoro says they have hygiene practices and policies to ensure that all food is prepared safely and to a high standard.

There are currently 879 inmates in the prison.