Nelson Marlborough Health said in the last four weeks, 24 cases had been notified to the Medical Officer of Health, compared to a range of 6-16 cases in the same period over the previous five years.
A number of known risk factors for campylobacteriosis had been identified in the people affected. These were: drinking raw (unpasteurised) milk or untreated water, and contact with animals and/or nappies.
Nelson Marlborough Medical Officer of Health Dr Stephen Bridgman advised people against drinking raw milk and said it was risky for anyone to consume, but young children and babies, older people, pregnant women and people with a weakened immune system were especially at risk of severe illness.
The public health service was working with the Ministry for Primary Industries, the Ministry of Health and the Institute of Environmental Science and Research to identify the reasons for the increase.
A single source cause was yet to be found and investigations were ongoing.