For the whole of last year 16 cases were reported there. And the jump in the rate of campylobactor at the factory has prompted an investigation.

Millions of chickens - a source of campylobactor - are killed at the factory each year.

Campylobactor, a notifiable disease, is a naturally occurring bacteria found in the gut of many animals. People who become ill with it suffer stomach cramps, nausea, headache, fever and diarrhoea. Symptoms can last from a day to a week and can have lasting consequences. Over the past nine years, 11 deaths have been associated with campylobactor in New Zealand.

This country has the highest reported rate of the disease in the developed world and it is estimated about 90 per cent of raw chicken has campylobactor.

However, Tegel assures there is no link between the campylobactor rates among staff in New Plymouth and levels of campylobactor on chicken leaving the factory.