Scientists at the University of Otago said in a statement that the country should ban fresh chicken to help cut down on the number of people hospitalized with camplyobacter.

The researchers compared human cases reported in New Zealand with data from other countries in 2003 and found it to have more than three times the rate of infection than neighbour Australia, and 30 times that of the United States.

But officials at New Zealand's Food Safety Authority (NZFSA) have reiterated that the actual source of the country's high number of cases is still not known. And poultry processors say they cannot therefore take all the responsibility for the rising infection rate.

"There's nothing in the farming practices or processing industry of New Zealand that is any different to anywhere else in the world,"<\i> said Michael Brooks, executive director of the country's poultry industry association (PIANZ).

"We acknowledge that campylobacter is present in poultry and that we should do something to tackle this but there is nothing in this new study to explain why chicken is the major cause of these cases," he told AP-Foodtechnology.com.

Campylobacter occurs naturally in the gut of birds, and chicken meat often becomes contaminated with the bacteria during slaughter and processing. If the meat is not cooked properly, the bacteria can cause severe stomach discomfort, diarrhoea, headaches and nausea in humans and can be severe enough to cause death or serious neurological damage, particularly in the old or very young.

Human cases of campylobacter have risen steadily in the last 20 years in many countries but no-one is sure why New Zealand, with a population of 4.1 million people, has such a high number of cases.

The EU, for example, recorded an average 47.6 cases per 100,000 people last year, a rise of 32 per cent since 2003. But in New Zealand, cases are now at a new high of 416 per 100,000 people, based on 15,553 cases recorded during the 12 months to May 2006.

And they seem to be rising faster than other regions too. In the last four weeks, reported cases doubled unexpectedly, according to the NZSFA.

"Data suggests that poultry is by far the most important food source but we don't have the data to show how important all other sources are," said Dr Roger Cook, principal microbiologist at the NZSFA.

Although around 90 per cent of fresh chicken available in supermarkets contains the bacteria, it can also be transmitted to humans through water, by handling animals and other environmental routes.

The NZFSA has commissioned two major studies as part of an international research project to gain a better understanding of the sources of campylobacter infection. These will gather isolates from human cases in specific regions of the country as well as water, animal sources and foods available in supermarkets at the time of the human infections.

The isolates are then put through molecular typing that allows the researchers to identify strains of the bacteria specific to chicken, for example, or other animals or sources. The first study, completing in a year's time, will give the authorities a much clearer idea of what is driving the current increase in infection.

But although there is no evidence yet to show why New Zealand's campylobacter cases are rising, Dr Michael Baker, lead author of the recent study, believes that the recent increase is likely to be linked to growing consumption of fresh chicken, which could be under-cooked by consumers and may be contaminating other foods.

New Zealanders eat more chicken than any other meat - 39.1 kg on average per year - and demand for poultry has been increasing by around 6 per cent each year, says the industry.

In a statement Dr Baker said that contaminated chicken is likely to be causing at least 50,000 cases of campylobacter infection in New Zealand each year and more than 400 hospitalisations, based on a previous large national study that found at least 50 per cent of disease could be attributed to chicken consumption.

"Let's make chicken the focus of our campylobacter control efforts. If we are successful in controlling that source we could potentially eliminate at least 50 per cent of cases. Once we have achieved that, then let's look at the other less important sources of infection," he said.

He called for fresh chicken - accounting for about three quarters of all chicken meat sold in New Zealand - to be banned from shelves and replaced by frozen chicken.

But while politicians reacted to the study by calling for tougher intervention from the food authorities, Dr Cook says only allowing frozen chicken is unlikely to be as successful in reducing campylobacter cases as other methods.

"Freezing chicken does lead to a drop in campylobacter but it is not a substantial drop compared to what we see with other methods," he said, adding that frozen chicken must be thawed properly before cooking and this process creates extra juices that can be spread around the kitchen, raising the risk of cross-contamination of other foods.

Dr Cook says that decontamination washes - where carcases are dunked into a solution of chemicals at the end of the slaughter process - are a more successful way of reducing campylobacter contamination.

"Work that the industry has done shows that this may reduce bacteria up to 100,000-fold, although it has been seen to change the quality of the chicken."

He said the food authority is also developing a risk assessment model to better evaluate where to intervene along the food production line.The industry says it is doing enough to tackle the problem, looking at farm interventions and leak-proof packaging of chicken meat, and also employing its own researchers to assess where the high number of cases is coming from.

But another author of the recent study, Dr Nick Wilson, believes the industry is procrastinating.

"There has been a tendency to blame the public for not handling poultry properly. This is like blaming the consumer who finds half a mouse in their meat pie. Fresh chicken sold in New Zealand is literally dripping with campylobacter," he said.

He pointed to a programme to reduce campylobacter contamination in Iceland's poultry in 2000 that involved freezing poultry from flocks which tested positive for campylobacter rather than allow it to be sold as fresh poultry after it had been slaughtered. These measures were followed by a significant decline in disease rates.

How the consumer responds to the current debate may however be the most influential factor on industry and regulatory action in this area.