Cattle linked to common stomach bug

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.

It typically keeps people sick for about a week.

In about one in every 1000 cases, the bug develops into a disease called Guillain-Barre Syndrome. This paralyses patients for weeks or months, leaves a fifth of its victims permanently disabled and kills 5 per cent of them.

The Ashburton study found campylobacter in 98 per cent of dairy cows' faeces, 84 per cent of beef cattle faeces, 65 per cent of duck faeces and 60 per cent of sheep faeces.

This meant that farmers who had any contact with animal faeces needed to be specially careful about washing hands before eating or smoking.

The levels of campylobacter in meat were much lower.

Red meat is generally safe, but the study looked at levels in the internal organs known as offal.

It found the main species of campylobacter in 5 per cent of pork offal, 9 per cent of beef offal and 36 per cent of sheep offal.

It also found it in 28 per cent of fresh chickens on sale in the district and in 55 per cent of rivers and streams.

"The animal and water components of this study have shown that New Zealanders living in rural South Canterbury live in an environmental sea of campylobacter," the study concluded.

"Any person living and working in this environment is likely to be heavily exposed to this micro-organism."

Dr Cook said that as well as doing further research on the sources of the bug, Environmental Science and Research was working on ways of reducing human infection from chicken.

Ideas include "crust freezing" techniques which could kill the bacteria without hardening the texture of the chicken.

"Overseas they have found that if you freeze the chicken it kills off a lot of the campylobacter," Dr Cook said.

"So we are looking at the effect of refrigeration, both chilled and frozen, to see if there are some effects that we can use to kill off campylobacter in chicken."

Environmental Science and Research scientists are also studying the way bacteria can survive in dehydrated potato which is heated with water to make potato pie toppings or potato and gravy in some fast-food outlets.