Doctors are seeing an increase in cases of acute stomach illness caused by the bacteria Yersinia pseudotuberculosis.
In a newsletter, the Royal New Zealand College of General Practitioners says cases have been seen in Auckland, Wellington and Christchurch, and some patients have been admitted to hospital.
Symptoms include abdominal pain, fever and sometimes diarrhoea.
The Ministry of Health website says Yersinia pseudotuberculosis bacteria can be spread by eating or drinking contaminated food or water and contact with infected faeces, contaminated soil or infected animals.