A case of mumps in the South Island could have already spread to others.

A person in the Marlborough area has been isolated due to suspicion they have the disease.

They were at the Blue Moon Lodge in Havelock on Christmas and Boxing Day, and at the Inlet Backpackers on Wednesday.

Public health officials are warning tourists in the area to check their immunisation status.

Medical Officer of Health Doctor Simon Baker said people need to stay alert to symptoms.

"Because this person stayed at backpackers it's very hard for our staff to actually trace people. They move on and no one knows where they've gone."

Baker said it also means there's a higher likelihood the disease has spread.

"Particularly when people are quite close together, and often in backpackers they are staying in dorms and sharing kitchens and bathrooms, people are closer together."

The news comes after an Auckland teen was misdiagnosed by doctors three times.

While still infected with mumps, she returned to work at a busy Auckland shopping centre, where she may have come into contact with 500 people.