New Zealand experienced a marked decline in campylobacteriosis incidence during 2007, with the 2008 notifications and hospitalization rates >50% lower than the averages for 2002–2006. This decline was sustained in 2009 (). This decreased incidence implies 70,000 fewer community cases in New Zealand in 2008 compared with the peak in 2006, on the basis of the widely used multiplier of 7.6× the number of notified cases occurring in the community (24
This reduction in incidence corresponds closely in time to the introduction of voluntary and regulatory interventions to reduce contamination of poultry with Campylobacter spp. Furthermore, patterns of the decline in disease incidence by population subgroup and area, along with the lack of plausible alternative explanations, suggest a causal effect from the poultry-focused interventions. The greater decline in campylobacteriosis in urban populations compared to the decline in rural populations () suggests that changes in foodborne transmission pathways were a key driver of the decline, compared with exposure pathways more likely to be encountered in rural settings (e.g., direct contact with contaminated environments or animals).
Source attribution modeling also provides supportive evidence that the decline in human campylobacteriosis can be largely attributed to a reduction in infection arising from poultry. The attribution study suggested a 74% decline in cases originating from poultry sources in 2008 compared with the baseline for 2005–2006. No statistically significant declines in attribution were found for any other sources ().
It is difficult to attribute the decline in poultry-associated human disease to any single intervention, because a range of food safety and poultry industry interventions were implemented since 2006. However, key informants identified the monitoring and reporting of Campylobacter spp. enumeration levels on poultry carcasses at the end of primary processing as particularly important, as well as the setting of mandatory performance targets.
The fall in campylobacteriosis rates in New Zealand is unusual in terms of the size and speed of the decline, and the regulatory measures that were used. Internationally, a small number of countries have reported declines in campylobacteriosis incidence following the implementation of control strategies focusing on poultry (25
). These countries have used various interventions, but a commonality has been strengthening on-farm biosecurity and monitoring the prevalence of Campylobacter
Although substantial evidence exists that poultry industry interventions contributed to the decline in campylobacteriosis incidence in New Zealand, several alternative explanations should be considered. These include the possibility of surveillance artifact, declining poultry consumption, declining disease associated with other foods or drinking water, effects of climate, and changes in consumer behavior.
Surveillance artifact is unlikely to have contributed significantly to the decline, however, given the magnitude of the reduction, the similarity of temporal trends in hospitalization and notification data (), the decline occurring across all population subgroups, and the lack of similar declines for the comparison group of notifiable enteric diseases (). Furthermore, the decline in campylobacteriosis in 2007 and 2008 was observed for all geographic areas (albeit to varying degrees), which suggests a change in a ubiquitous and common exposure. Salmonellosis rates may also have been expected to fall because of the potential concomitant effects of the interventions on Salmonella
spp. contamination of poultry. However, the lack of decline in salmonellosis is not surprising in the New Zealand context because Salmonella
spp. contamination levels were very low in poultry before the implementation of these interventions (29
To assess the possible impact of poultry consumption on the decline in campylobacteriosis, we examined poultry production data. In New Zealand, poultry production approximates poultry consumption because of the closed nature of the production system. Over the period of the marked decline in campylobacteriosis incidence (2006–2008), fresh poultry production waned by only 5.8% (30
). While this fall in production could have affected the incidence of poultry-associated foodborne campylobacteriosis, it is unlikely to be sufficient to explain the >50% drop in campylobacteriosis notifications occurring over this period.
Several foodborne pathways of campylobacteriosis (other than poultry) have been identified, including red meat and raw milk consumption (9
). The contribution of these pathways to sporadic campylobacteriosis in New Zealand has been estimated to be markedly less than that of poultry (9
). The magnitude of the decrease seen in 2008 is such that even if the contributions from food sources other than poultry had been eliminated in their entirety, they likely could not account for the observed decline in campylobacteriosis.
Contaminated water and other environmental sources have been implicated as a transmission pathway of human campylobacteriosis (32
). Although water is found to be contaminated with Campylobacter
spp., molecular epidemiologic studies have shown a low similarity between these genotypes and those found in human case-patients, suggesting that the strains detected in water are relatively apathogenic or that humans have limited exposure to them (12
). Furthermore, a high proportion of New Zealanders receive treated community water supplies, with only small gradual increases in the proportion receiving water that meets microbiological quality criteria (34
Changes in consumer behavior (e.g., hygiene, food preparation, eating out) could have plausibly contributed to the decline. However, challenges in altering consumer behavior have been acknowledged (35
), and, given the rapidity of the decline in incidence, it is unlikely a sudden, marked change in consumer behavior could have been a key driver of the decline.
The effect of climate was considered as a possible driver of the decline. Despite the seasonal pattern observed for campylobacteriosis, the main drivers of the association between climate and campylobacteriosis remain elusive (36
). However, the rapidity of the fall in incidence suggests that global climate change factors are unlikely to be key drivers.
A strength of this study is the multiple data sources that were accessed and analyzed, including source attribution techniques and key informant interviews. Nevertheless, a limitation of this study in determining the likely cause of the recent decline in campylobacteriosis is the descriptive nature of the epidemiologic analysis and the complex epidemiology of campylobacteriosis, which means that not all factors that might influence the disease’s incidence were examined explicitly. Although validated by studies in 2 other regions, the source attribution analyses were from 1 sentinel site only, and this work also has its own limitations (12
). A further weakness is that details of specific industry-level interventions to reduce poultry contamination are not in the public domain, and therefore cannot be examined in detail. We were also unable to examine in detail data on Campylobacter
spp. contamination levels in poultry. However, summary microbiological data on Campylobacter
spp. contamination levels from the national database for 2007 and 2008 as published in the updated Campylobacter
Risk Management Strategy 2010–2013 (23
) support a reduction in Campylobacter
spp. prevalence and counts on poultry over the period of the decline.
Rates of campylobacteriosis have shown marked annual variations in the past, so it will be important to assess medium- to long-term trends in disease and its attribution to assess the effects of NZFSA’s strategy. Notification and hospitalization data for 2009 indicate that the decline in incidence seen in 2008 has been largely sustained (). Despite the 2009 rates being slightly higher than those of 2008, they still represent a substantial decline compared with the average for 2002–2006 (48% for notifications and 50% for hospitalizations).
Although there are costs associated with implementing industry regulation, these are likely to be offset by both the direct and indirect savings from reduced disease effects and lost productivity, conservatively estimated to have cost NZ$600 per campylobacteriosis case in 2005 (37
). Given an estimated 70,000 fewer cases of campylobacteriosis in the community in 2008 than in 2006, this decline represents notable savings to New Zealand society. While progress has been made in responding to New Zealand’s campylobacteriosis epidemic, the costs and effects are still significant. As such, further research (including evaluating additional interventions) is desirable from a public health perspective to enable continued reductions of the still high burden posed by campylobacteriosis.
The findings of this study provide evidence of a successful population-level food safety response to a serious public health issue. New Zealand has experienced a prolonged national epidemic of campylobacteriosis. Fresh poultry was implicated as the dominant source, and a range of voluntary and regulatory interventions were introduced to reduce Campylobacter
contamination of poultry. The apparent success of these interventions demonstrates approaches other countries could consider for controlling infectious disease epidemics linked to specific food sources. This example highlights the importance of integrated public health surveillance that includes upstream hazards as well as disease (38
). Finally, the success of the response shows the value of collaboration between industry, food safety regulators, and public health researchers in addressing important food safety issues.