Risk factors for the colonization of broiler flocks with Campylobacter in Iceland
This thesis is an investigation of risk factors associated with the colonization of broiler flocks with 'Campylobacter' in Iceland. A longitudinal study was carried out between May 2001 and September 2004. Pooled caecal samples were obtained from 1,425 flocks at slaughter and cultured for 'Campylobacter. ' Due to the strong seasonal variation in flock prevalence, analyses were restricted to flocks raised during the four summer seasons. Initial analyses focussed on particular aspects of production; broiler house attributes and management practices, farm-level factors, and temperature-related factors based on thresholds of fly activity. Potentially important predictors identified from the initial studies, as well as several flock-level variables, were included in a logistic regression analysis, with random effects at the house and farm levels. The risk of flock colonization was predicted to increase when the house was cleaned with geothermal water, when boots were cleaned and disinfected before entering the house, with increasing age at slaughter, with increasing flock size, and with increasing cumulative degree-days above an average temperature of 4.4°C during the 2 to 4 week period before slaughter. Protective factors included the presence of at least one cool day (a maximum temperature below 8.9°C) during the same period before slaughter, and an official (municipal) treated water source compared to an untreated source. A non-official treated water source was marginally protective. Analysis of variance components revealed that differences among farms accounted for a significant amount of the variation in flock status. The farm-to-farm variation was explained by two factors, the use of geothermal water for cleaning, and water source/treatment. Geothermal water may be a surrogate for micro-climatic conditions or agro-environmental pressures on the farm and surrounding region. Further studies directed toward identifying underlying environmental factors, and treatment of the broiler's water supply may provide the means to substantially reduce 'Campylobacter ' in broiler flocks in Iceland. Additional interventions that require investigation include fly control during high risk periods (i.e. periods of sustained high temperatures with minimal cool days), shipping flocks at a younger age, and limiting flock sizes. Boot dipping procedures should be examined on farms experiencing a high prevalence of 'Campylobacter.'