Risk Factors for <i>Campylobacter</i> on Broiler Farms

Lay summaryCampylobacter is the leading cause of food poisoning in the UK, with chicken meat being the most common source of Campylobacter exposure.Campylobacter does not cause illness in chickens, and is widespread in chicken farms, with 60% of UK broiler flocks carrying Campylobacter by the time they are slaughtered.Reducing Campylobacter in broiler flocks is therefore potentially an opportunity to reduce human exposure to Campylobacter via chicken meat.This review, which formed part of a wider assessment of interventions to reduce Campylobacter in chicken meat across the processing chain, looked at evidence for practices which could reduce the prevalence of Campylobacter in broiler flocks.Farm management measures such as preventing unnecessary entry into broiler houses, using dedicated boots and clothing, and cleaning hands and footwear were found to reduce the risk of Campylobacter entering the flock.However, the studies did not show which measures work best, and many highlighted the challenge of maintaining these practices, especially under real farm conditions.Removing a proportion of a flock early for slaughter (to cater for demand for smaller birds), and poor cleaning between flock cycles, especially in older or lower-quality housing, were also linked to higher levels of Campylobacter in broiler farms.Campylobacter may also spread during transport of chickens to the slaughterhouse, due to stress, close crowding or poorly cleaned transportation equipment.Other potential sources, such as feed, water, litter or parent birds, appeared to be less important.Evidence for the effect of other domestic animals on the farm, or wildlife or pests, was mixed, although adjacent broiler houses were found to increase the risk of Campylobacter.Overall, this review found that good hygiene and farm management practices remain the best tools available, but that further research is needed to understand how Campylobacter spreads on broiler farms and which interventions can best reduce its prevalence. Executive SummaryAn umbrella review, based on three systematic reviews which included meta-analysis and two systematic reviews with qualitative outcomes, was conducted to evaluate the evidence for risk factors for Campylobacter prevalence in broiler farms.This umbrella review focused on eight risk factor categories: animal-related; vertical transmission; water, feed & litter; environmental; equipment & vehicle, external & regional; farm management & biosecurity; and pests & wildlife.Quantitative assessment of different risk factors was limited due to variabilities in study design, methodologies and outcomes measured across the included reviews as well as the analytical tools chosen for this study; further quantitative analysis or meta-analysis is recommended for drawing robust conclusions.Farm management & biosecurity was highlighted by all reviews as a crucial factor in controlling Campylobacter colonisation, although there was a lack of quantitative prevalence estimates to support this.While there was evidence for transmission between broiler flocks and adjacent domestic animals, wildlife and pests, and external environmental sources, the relative importance of these transmission routes and the directionality of spread could not be determined.Transmission of Campylobacter during transport from the farm to slaughterhouse was also identified as a risk factor.Vertical transmission, feed, water and litter were not determined to be important risk factors, although they cannot be ruled out in rare cases.Overall, this report highlights the need for high-quality, standardised studies investigating the sources of Campylobacter in broiler houses, including investigations into genetic linkage and the directionality of spread, and the effectiveness of biosecurity and hygiene interventions in preventing colonisation of broilers by Campylobacter from animals and external environmental sources.