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Campylobacter spp., especially Campylobacter jejuni and C. coli, are the main cause of human bacterial gastroenteritis in the developed world (http://www.who.int/mediacentre /factsheets/fs255/en/). Chicken meat is frequently contaminated with Campylobacter (19), and it is a commonly held view that reducing the number of flocks infected with this organism would reduce the number of human Campylobacter cases. A better understanding of the epidemiology of Campylobacter in broiler flocks is required in order to design successful control programs at the farm level.In some European countries, flock colonization of chickens with Campylobacter has a clear seasonal pattern, with highest rates seen in the summer or autumn (20). Studies in the United Kingdom in the early 1990s suggested that there was no increase in the proportion of flocks colonized with campylobacters in warmer months (21, 28). However, we recently found that housed flocks were more likely to be Campylobacter positive in summer (46) in a geographical subset of the data in this study, and evidence of seasonality was also found in 401 batches reared in the United Kingdom in 2008 (20). The reasons for the seasonal variation are not fully understood but are likely to involve the frequency and nature of exposure of the flocks to Campylobacter spp. There is further evidence that climatic factors such as temperature correlate with both broiler flock and human infections (36,43,52). Temperature could also affect the environmental sources of Campylobacter spp. to which broiler chickens may become exposed. A better understanding of the roles of season and climatic factors and their relative impacts on broiler flock colonization with Campylobacter will be useful for policy makers and broiler companies who are formulating control programs to reduce flock infection with this important zoonotic pathogen.Typing of isolates from foods and clinical cases has provided evidence that many strains isolated from chickens share attributes with those from human cases (13,25,37). Multilocus sequence typing (MLST) has been used to assess the relative importance of sources, reservoirs, and transmission routes for human Campylobacter infection in the United Kingdom (48,56). The population of Campylobacter isolates from human cases in England has been well analyzed by studies of isolates from Ͼ2,900 cases from three areas spanning the years 2000 to 2006 (14, 56). However, data sets for strains from chicken flocks at slaughter were smaller and may have been less representative. For example, while 307 chicken isolates were cited

The 2011 EFSA opinion on Campylobacter was updated using more recent scientific data. The relative risk reduction in EU human campylobacteriosis attributable to broiler meat was estimated for on‐farm control options using Population Attributable Fractions (PAF) for interventions that reduce Campylobacter flock prevalence, updating the modelling approach for interventions that reduce caecal concentrations and reviewing scientific literature. According to the PAF analyses calculated for six control options, the mean relative risk reductions that could be achieved by adoption of each of these six control options individually are estimated to be substantial but the width of the confidence intervals of all control options indicates a high degree of uncertainty in the specific risk reduction potentials. The updated model resulted in lower estimates of impact than the model used in the previous opinion. A 3‐log10 reduction in broiler caecal concentrations was estimated to reduce the relative EU risk of human campylobacteriosis attributable to broiler meat by 58% compared to an estimate larger than 90% in the previous opinion. Expert Knowledge Elicitation was used to rank control options, for weighting and integrating different evidence streams and assess uncertainties. Medians of the relative risk reductions of selected control options had largely overlapping probability intervals, so the rank order was uncertain: vaccination 27% (90% probability interval (PI) 4–74%); feed and water additives 24% (90% PI 4–60%); discontinued thinning 18% (90% PI 5–65%); employing few and well‐trained staff 16% (90% PI 5–45%); avoiding drinkers that allow standing water 15% (90% PI 4–53%); addition of disinfectants to drinking water 14% (90% PI 3–36%); hygienic anterooms 12% (90% PI 3–50%); designated tools per broiler house 7% (90% PI 1–18%). It is not possible to quantify the effects of combined control activities because the evidence‐derived estimates are inter‐dependent and there is a high level of uncertainty associated with each.

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Campylobacter is the most common known source of human bacterial enteritis in the developed world and poultry is considered the main source. Broilers often become colonized with Campylobacter during rearing, and then contaminate the farm environment. The objective of this study was to identify Campylobacter-positive environmental reservoirs on farms, as these pose a risk to broiler flocks becoming colonized with Campylobacter. We considered the temporal aspects of exposure and colonization. A longitudinal study monitored six conventional rearing farms over 2 years. The broiler flocks, catchers' equipment, vehicles, shed surrounds, shed entrance, other equipment, farm entrance, other animals, puddles, dead birds, mains water and drinkers were systematically sampled 2-4 times per flock. A multivariable generalized estimating equation model was used to assess associations between contaminated environmental sites and colonized broiler flocks. The associations were adjusted for confounders and other known risk factors. To further assess temporality of contamination, the sequence of contamination of the different environmental sites and the flocks was established. Contaminated shed entrances and anterooms, contaminated drinkers and shedding of Campylobacter by other animals such as cattle, dogs, wildlife and rodents were significantly associated with positive flocks. The reservoir of 'other animals' was also the reservoir most commonly positive before the flock became colonized. The other sites usually became contaminated after the flock was colonized.