Cattle are an unexpected source of food poisoning.

Cattle are an unexpected source of food poisoning.

Cows are an unexpected source of food poisoning.

Cows - New Zealand's main export producers - have been revealed as unexpected carriers of the most prevalent stomach bug, campylobacter.

The number of food poisoning cases caused by campylobacter has quadrupled in New Zealand in the past 15 years and is now five times Australia's rate and almost 10 times that of Canada.

Experts assumed the increase was related to the growing popularity of chicken, a prime source of the bug.

The average New Zealander eats 36kg of chicken a year, compared with 15kg 10 years ago.

But an Institute of Environmental Science and Research study, published quietly by the Ministry of Health two years ago, found that the biggest risk factor for campylobacter in the rural district of Ashburton was contact with cows.

Eating chicken is still believed to be the main cause of campylobacter in urban areas.

The finding was unearthed during a Herald inquiry into what is in our food and why New Zealand has the highest food poisoning rate in the developed world.

The Ashburton study suggests that New Zealand's livestock-based economy may be a big contributor to these high rates.

It recommends that farmers should:

* Stop drinking raw milk taken directly from cows on the farm.

* Stop drinking untreated water.

* Wash their hands before eating or smoking after contact with animals.

The Food Safety Authority's principal adviser for food microbiology, Dr Roger Cook, said the findings did not threaten New Zealand's dairy and meat exports, which were processed or frozen.

The authority has commissioned nine further reports from Environmental Science and Research to follow up the Ashburton study.

These will include a discussion document on the main sources of campylobacter, to be published in March.

The authority says contact with animals, drinking untreated milk and water, and swimming in contaminated water appears to be "equally, if not more responsible" than eating chicken and other foods for most cases.

Campylobacter is a bacterium that causes diarrhoea, stomach cramps and fever two to four days after infection.