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| Journal of the New Zealand Medical Association,
13-October-2006, Vol 119 No 1243
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Regulation of chicken contamination urgently needed
to control New Zealand’s serious campylobacteriosis
epidemic
Michael Baker, Nick Wilson, Rosemary Ikram, Steve Chambers,
Phil Shoemack, Gregory Cook
Imagine you were asked to investigate an epidemic of disease
that was causing at least one death a year in New Zealand, putting over 800
people in hospital, causing in excess of 15,000 notified cases, and a further
100,000 non-notified cases. Also imagine that your epidemiological and
laboratory investigation implicated a single food as the source for a large
proportion of these cases. Imagine that systematic testing of this widely
consumed food showed that it was routinely contaminated with the pathogen
causing this illness, often with thousands of organisms on each piece in its
pre-cooked state. Imagine you also found that cross-contamination in kitchens
was very hard to prevent and likely to occur in thousands of instances each
year. At this stage you would recommend the immediate withdrawal of this food
from the market and recall of contaminated batches to prevent as many cases of
disease as possible.
We do not need to imagine this scenario, as this is reality
for New Zealand in 2006. This paper outlines the scale of New Zealand’s
campylobacteriosis epidemic, the importance of fresh chicken as a major source
of this infection, and why we consider that this food should be withdrawn from
sale in New Zealand until it can be shown to pose a low risk to human
health.
New Zealand’s campylobacteriosis epidemicOur epidemic of campylobacteriosis reached a new high point
in May 2006 when the annualised national notification rate exceeded 400 per
100,000 for the first time, based on 15,553 cases for the preceding 12
months.1 (see Figure 1)
Rates in New Zealand were already the highest reported by
any country, being more than 3 times higher than in Australia and 30 times
higher than the United States.2 Many other
developed countries use surveillance methods that are as rigorous as those used
in New Zealand, so there is no basis for concluding that we are just better at
diagnosing and reporting this disease.
The health impact of campylobacteriosis now places it among
New Zealand’s most important infectious disease problems.
Campylobacteriosis caused more hospitalisations in 2005 than meningococcal
disease, acute rheumatic fever, AIDS, and tuberculosis combined (based on
principal diagnosis).3 The total number of
campylobacteriosis cases in the community is conservatively estimated at 115,000
per annum (based on a widely used multiplier of 7.6 times the number of notified
cases,4 although some countries have used
multipliers as high as a 100 times5).
Campylobacteriosis also kills. There is about one recorded
fatality a year from the acute effects of this
disease.3 Chronic effects include
Guillain-Barré syndrome (GBS), the risk of which is greatly increased (by
77 to 100
times6,7) in
the 2 months following Campylobacter infection. GBS is fatal for
4–15% of patients and leaves around 20%
disabled.8
We also estimate that this epidemic is costing New Zealand
about 75 million dollars a year, based on an update of a previously published
costing estimate9 ($533 per case in 1999,
updated using consumer price index movements to $632 in 2006 and applied to the
increase in estimated cases).
Figure 1. Annual number of notifications
(1980–2005) and hospitalisations (1995–2005) for campylobacteriosis
in New Zealand
 Source: Institute of Environmental
Science and Research Limited (notifications) and New Zealand Health Information
Service (hospitalisations, based on principal diagnosis).
What can be done to control this epidemicThe obvious control measure is to swiftly remove fresh
chicken from the food supply and only reintroduce it when it can be shown to
pose a very low risk to human health. Frozen chicken (or other processed forms
with reduced contamination levels) could be substituted, in the interim, to
allow continued consumption of this popular food. While this might appear a bold
public health step, we think it is fully justified for the reasons outlined
below.
Contaminated chicken meat has a central role as the source
of the Campylobacter epidemic. Two separate New Zealand case-control
studies of sporadic disease have specifically implicated this
source.11,12 One of these was a large
multi-centre study that found that chicken-related exposures could explain over
half of the population attributable risk, more than all of the other risk
factors combined.12 Other New Zealand
epidemiological studies of sporadic campylobacteriosis and of outbreaks, often
with supportive laboratory evidence,13–16
are also consistent with an important role for chicken as a risk
factor.17
The rise in campylobacteriosis over the last 25 years has
coincided with a substantial increase in poultry consumption (Figure 2). Most of
this increase has been in fresh chicken meat, which rose from 4 kg/person in
1981 to 30 kg/person in 2005, and now accounts for 80% of total production.
Campylobacteriosis incidence is highly correlated with this increase in fresh
chicken meat production (Spearman’s rank correlation coefficient
rs= 0.98, p < 0.0001).
Figure 2. Annual production (tonnes) of fresh
and frozen chicken meat in New Zealand (1981–2005)
 Source: Statistics New Zealand
quarterly survey of poultry producers. Note that because almost all NZ chicken
production is destined for human consumption within NZ, and virtually no chicken
is imported, these data correspond well to human consumption
patterns.10
Although human campylobacteriosis can come from a multitude
of sources (contaminated food, water, or environments—or contact with
infected humans or animals), no source except for chicken has been implicated in
more than a few percent of cases in New
Zealand.11,12,18 Overall notification and
hospitalisation rates are higher in cities than in rural areas, which is also
consistent with a largely food-borne illness rather than one from contact with
contaminated environments, animals, or water.2
For those living in rural areas, non-poultry sources of
infection (such as direct zoonotic infection from farm animals) are likely to be
relatively more important than for those living in
cities.19 However, the rural population
accounts for only 14% of the total New Zealand
population,2 and many of those will still
consume and be infected from commercially produced chicken in the same way as
those living in urban areas.
There is good evidence that withdrawing fresh poultry from
the market would greatly attenuate this epidemic. There is a famous
‘natural experiment’ from Belgium where poultry was removed from the
market for 4 weeks in 1999 because of a scare over dioxin contamination. The
incidence of Campylobacter infection in that population dropped by 40%
from the expected rate, and then returned to ‘normal’ when poultry
was reintroduced.20
In 2000, Iceland introduced an intervention similar to the
one we are advocating. This intervention included testing chicken flocks and
only allowing those that were ‘Campylobacter-free’ to be
sold as fresh chicken. The remaining contaminated chicken could only be sold
frozen. This intervention was followed by a substantial decline in reported
campylobacteriosis.21,22 This approach is also
being used in Denmark and Norway.23 Evaluating
the net effectiveness of this intervention has been complicated by the fact that
it has been introduced with varying degrees of rigor, often along with other
control measures.21
Freezing chicken is not a perfect solution. While it does
not eliminate Campylobacter contamination, it has been found to
markedly reduce levels of the organism in chicken meat (by 0.5 to >2.5 logs,
or approximately a 3 to >300 fold reduction in contamination levels depending
on the methods used 5,22–26). If
introduced it would work in combination with current control measures, including
cooking and careful food handling.
Quantitative risk assessment in Denmark suggests that a drop
of about 100-fold in Campylobacter contamination levels of fresh
chicken is enough to reduce the risk to consumers by about
30-fold.5 Preliminary results from similar
modelling carried out in New Zealand also shows that freezing poultry would
considerably reduce the predicted number of human
infections.27
In addition, previous research in New Zealand has shown that
using frozen chicken protects people from illness, presumably because people
doing this are not handling and consuming fresh
chicken.12 Applying this risk-reduction
strategy in New Zealand could mean that instead of fresh chicken potentially
causing 59,000 cases of illness each year, it might only cause 2000 cases (based
on current incidence, using a conservative estimate of 50% of cases attributable
to chicken meat exposure,12 and a 2 log
reduction in contamination through use of effective
freezing5).
Freezing, or using some other proven method to decrease
contamination levels in fresh poultry, appears to be the only plausible way of
reducing illness from this source in the short-term. The current approach of
waiting for the poultry industry to lower contamination levels doesn’t
appear to be working. Surveys of fresh chicken in New Zealand show that
contamination is routine and appears to be at high levels (89% of 250 chicken
meat samples collected in a national retail survey in 2003–4 were
contaminated28). Programmes to prevent poultry
colonisation on the farm offer potential to reduce contamination levels, but may
take years to implement.29 Reducing
contamination in poultry slaughter houses has also proven
difficult.30
Educating those who prepare chicken at home and in
restaurants to take precautions with handling chicken is important, but it is
unlikely to significantly reduce infection rates because of the acknowledged
difficulty of changing consumer behaviour,31
and because of the technical difficulties of preventing cross-contamination in
the kitchen setting. Kitchen contamination studies show that preparation of
meals with raw chicken results in cross contamination to hands, plates, chopping
boards, utensils, and ready to eat food.32
Preparing fresh chicken also results in very widespread distribution of
Campylobacter in the kitchen environment and this organism can be
recovered from kitchen surfaces 24 hours later. Simple cleaning with hot water
and detergent does not appear to be sufficient to clean these surfaces, and the
use of a chlorine-containing disinfectant appears
necessary.33
Switching to frozen chicken will pose challenges for chicken
producers and may be unpopular with some consumers, but is certainly not
technically difficult to implement. Frozen chicken was the main form of retail
chicken product in New Zealand up until the late 1980s and still accounts for
about 20% of chicken sold in this country (Figure 2). The poultry industry could
certainly be permitted to find alternative processing methods that achieved the
same levels of microbial reduction as freezing. It will also be necessary to
review and monitor the methods used to freeze poultry as some methods achieve
much higher levels of organism reduction than
others.22,25
The requirement to achieve low Campylobacter
contamination levels in chicken meat, through freezing or other methods, offers
the huge advantage of rewarding producers who deliver safer food. Currently
there is little or no financial incentive for industry to invest in methods to
lower such contamination. These bacteria are invisible to consumers and
restaurant staff, who cannot therefore assess (and potentially pay a premium
for) ‘Campylobacter-free’ product to lower the risk to them
and their customers.
Allowing producers who achieved low contamination levels to
continue to distribute fresh chicken would give them a strong economic incentive
to develop and implement methods to reach this goal. Given the very large cost
of this epidemic, there would be a net economic benefit to New Zealand society
from spending tens of millions of dollars on implementing such control measures.
As a major food producing and exporting country, we should
be a world leader in controlling food-borne diseases like campylobacteriosis.
Our current status at the top of the campylobacteriosis league table must be
highly embarrassing for our critical food production sector.
ConclusionsMany of New Zealand’s important epidemics are
difficult to control. The epidemics of diabetes, road traffic injuries, and some
forms of cancer have complex origins and preventing them will take all of our
collective ingenuity, not least because they involve sustained changes in human
behaviour and extensive modifications to our environment. By contrast, the New
Zealand campylobacteriosis epidemic is relatively easy to control because it can
be greatly reduced by managing a single dominant source. There are parallels
with the famous public health intervention of taking the handle off the public
water pump to control the London cholera outbreak of 1854 (this is a slight
simplification of historic events, but it illustrates the principle of
controlling epidemics by identifying and managing their
source34).
Given this evidence, we call on the New Zealand Food Safety
Authority to remove fresh chicken from sale until it shows
Campylobacter contamination levels that are consistently below a
specified maximum regulatory level. This change in policy could permit the
continuing distribution of frozen chicken, which we suggest should be
accompanied with large pictorial health warnings and instructions on each
package about correct thawing and cooking.
We also recommend that these changes be accompanied by a
rigorous evaluation programme to measure their impact on reducing the high
health burden of campylobacteriosis in the New Zealand population. The poultry
industry could assist by making the results of their extensive microbiological
testing programme available to researchers. Evaluating interventions to reduce
disease risk should take precedence over further research on Campylobacter
transmission pathways and microbiology.
New Zealand has the opportunity to act decisively to control
a serious public health problem. To not act would mean accepting the serious
ethical, health, and economic consequences. Such inaction could only be
justified if the arguments presented here can be convincingly refuted by sound
evidence for alternative courses of action.
Author information: Michael G Baker, Nick
Wilson, Public Health Physicians; Wellington School of Medicine and Health
Sciences, University of Otago, Wellington; Rosemary Ikram, Clinical
Microbiologist, Medlab South, Christchurch; Steve Chambers, Professor of
Pathology, Christchurch School of Medicine, University of Otago, Christchurch;
Phil Shoemack, Medical Officer of Health, Bay of Plenty District Health Board,
Tauranga; Gregory Cook, Associate Professor, Department of Microbiology and
Immunology, University of Otago, Dunedin.
Correspondence: Dr Michael Baker,
Department of Public Health, Wellington School of Medicine and Health Sciences,
PO Box 7343, Wellington South. Fax: (04) 389 5319; email: michael.baker@otago.ac.nz
References:
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