Study reveals New Zealand campylobacter rates highest in world
Three times higher than Australia; 30 times higher than the US
09 July 2006
University of Otago public health researchers say New Zealand should seriously consider banning the sale of fresh chicken for human consumption, and switch to frozen chicken instead, to alleviate the country's serious campylobacter epidemic.
A study by the University's Wellington School of Medicine and Health Sciences' researchers just published in the international journal Epidemiology and Infection paints an alarming picture about the rate of campylobacter infection in New Zealand. Infection rates have risen steadily for more than two decades and are now more than three times higher than that reported in Australia and 30 times higher than the United States. This is the first time that New Zealand's comparative situation has been quantified and comprehensively reported in an international peer-review journal. Since the research was completed, rates have risen to a new high of 416/100,000 for the 12 months ending May 2006, based on 15,553 cases notified during that period.
Lead study author Dr Michael Baker says New Zealand now has the dubious distinction of having the world's highest reported rates of campylobacter infection. "Immediate action is needed to control New Zealand's epidemic of campylobacter infection. In addition to food hygiene, we actually need to deal with the source of the infection."
The study reported that the rise in notifications was matched by a similar rise in hospitalisations for this infection - suggesting that the increase in disease rates is real, rather than being caused by better surveillance.
Dr Baker says the causes of this increase are not known for sure, but are likely to be linked to the rise in consumption of fresh chicken. A recent report, commissioned by the New Zealand Food Safety Authority, noted that up to 90 per cent of fresh chicken sold for consumption is contaminated with campylobacter. The risk is not from properly-cooked chicken, but largely from under-cooked chicken and foods that have been cross-contaminated from fresh chicken.
Dr Baker estimates 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. He bases this estimate on a previous large national study that found at least 50 per cent of disease could be attributed to chicken consumption - more than all of the other risk factors combined. Overseas studies have found that that the real rate of campylobacter in the community is seven-to-eight times higher than the number of notified cases, suggesting there are now more than 100,000 cases of campylobacter infection in New Zealand each year (based on 13,839 notified cases in 2005 and 871 hospitalisations).
"Chicken has become the cheap and dirty food of New Zealand," Dr Baker says. However, he suggests that, while it may be cheap to buy, the estimated cost of campylobacter to New Zealand today is $70 to 80 million, of which chicken consumption is likely to be responsible for at least half.
Dr Baker urges two key approaches to reduce the harm from the campylobacter epidemic. "First, we have to acknowledge that contaminated chicken is the major cause of this epidemic. A good start would be an open public dialogue between the poultry industry, regulators, scientists and consumer organisations about the scale of the problem and how to address it using proven methods.
"Second, we should immediately switch to frozen poultry and seriously consider banning the sale of fresh chicken for human consumption, unless it can be shown to have minimal contamination. Freezing chicken greatly reduces contamination levels."
Dr Baker also advocates a research programme to evaluate the impact of any switch to frozen poultry. "That way we would know at the end of the day how much illness had been prevented."
One of the study co-authors, Dr Nick Wilson, who has observed the debate about the causes of New Zealand's campylobacter epidemic for more than 10 years, says he is dismayed at the level of procrastination by industry. He cites two misconceptions which he has seen used to justify these delays.
"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. Everything that raw chicken touches can become cross-contaminated to the extent that even a spotlessly well-run home kitchen or restaurant can become a source of infection. We have to move away from this kind of victim blaming.
"The second misconception I have heard over and over again is that chicken is just one of many sources, so should not be singled out. This is like the tobacco industry saying that smoking is not the only cause of lung cancer. While it is technically correct, it diverts attention away from the main cause. 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."
To support these arguments Dr Baker cites two well-documented examples from overseas. The first example was a "natural experiment" in Belgium where poultry was withdrawn from the market for four weeks in 1999 because of concerns that it might be contaminated with dioxin. Rates of campylobacter infection fell by 40 per cent during this ban, and then returned to the previous level after chicken was put back on the shelves.
A second example comes from Iceland, where a comprehensive programme to reduce campylobacter contamination in its poultry was introduced in 2000. This programme included 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. New Zealand, like Iceland, is an island country that produces its poultry locally so such measures should work here.
Dr Baker says it is completely unacceptable to sell a food that is heavily contaminated with bacteria that is making thousands of New Zealanders sick each month. "We know enough to act now to control this epidemic. I would never let unfrozen poultry into my house."
Other findings reported in the paper:
Campylobacter infection reached a peak of 14,790 cases in 2003, a rate of 396/100,000 population.
Corresponding rates in other countries were: Australia (117/100,000 in 2003), England and Wales (85/100,000 in 2003), Scotland (87/100,000 in 2003, Iceland (116/100,000 in 2000), Netherlands (37/100,000 in 2001), United States FoodNet sites (13/100,000 in 2003), and Canada (40/100,000 in 2000)
Rates of campylobacter notification are highest in children under 5 years and young adults (20-29 years). Hospitalisations also have a peak in the elderly (those 70-plus years).
Rates are significantly higher in males.
Rates are significantly higher in Europeans than in Maori and Pacific People, unlike many serious infections that tend to have higher rates in Maori and Pacific populations.
Rates are significantly higher in urban areas compared with rural populations for both notifications and hospitalisations.
The highest notification rates were in Wellington and South Canterbury district health board areas. Both districts had annual notification rates >400 / 100 000 (based on average for 2001-2003).
For more information, contact
Michael Baker
Senior Lecturer
Department of Public Health
Wellington School of Medicine & Health Sciences
University of Otago
Tel 64 4 385 5541 extn. 6802
Email michael.baker@otago.ac.nz
Brigid Feely
Communications Manager
University of Otago
Tel 64 3 479 8263
Email brigid.feely@otago.ac.nz
