No association between partial depopulation and Campylobacter spp. colonization of Dutch broiler flocks A.D. Russa 1 , A. Bouma 1 , J.C.M. Vernooij 1 , W. Jacobs-Reitsma 2 and J.A. Stegeman 1 1 Department of Farm Animal Health, Faculty of Veterinary Medicine, Utrecht University, Yalelaan, Utrecht, the Netherlands, and 2 Animal Sciences Group, Wageningen University and Research Centre, Lelystad, the Netherlands 2004/0758: received 1 July 2004, revised and accepted 27 April 2005 ABSTRACT A.D. RUSSA, A. BOUMA, J.C.M. VERNOOIJ, W. JACOBS-REITSMA AND J.A. STEGEMAN. 2005. Aims: To determine whether an association exists between partial depopulation of a flock and increased Campylobacter colonization in that flock. Methods and Results: Data from 1737 flocks of two Dutch integrators were used. Flocks that experienced partial depopulation were defined as ‘exposed’ and those that did not as ‘nonexposed’. Multivariable modelling was accomplished with, in addition to ‘exposure’, the independent variables ‘age of broilers at slaughter’ and ‘season’ to adjust for possible confounding. The response variable was ‘Campylobacter colonization’. The odds ratio (OR) for partial depopulation for integrator A was 0Æ8 [95% CI (0Æ4, 1Æ8)]; for integrator B the OR ¼ 0Æ8 [95% CI (0Æ5, 1Æ3)]. Age and season were confounders: the difference in Campylobacter status between exposed and nonexposed flocks of integrator A could be explained by both variables; for integrator B, only season was associated with Campylobacter status. Conclusions: We found no significant association between partial depopulation and an increased risk of Campylobacter colonization among broiler flocks at final depopulation. Significance and Impact of the Study: This study demonstrates that Campylobacter colonization in a broiler flock is not influenced by the partial depopulation of that flock. Keywords: broilers, Campylobacter, epidemiology, partial depopulation, risk factors, zoo ¨noses. INTRODUCTION Campylobacter species are a major cause of food-borne gastrointestinal infections in humans (World Health Organ- ization 2000). An important source of human Campylobacter infections is the handling and consumption of undercooked contaminated chicken meat (e.g. Kapperud et al. 1992; Eberhart-Phillips et al. 1997; Evans et al. 1998; Allos 2001; Neimann et al. 2003). Consequently, an important contri- bution to the reduction of the exposure of humans could be obtained by a reduction of Campylobacter colonization of broiler flocks. Although the exact contamination sources and transmis- sion routes of Campylobacter are still unknown, many risk factors with respect to increased Campylobacter coloniza- tion have been identified (e.g. Kapperud et al. 1992, 1993; Jacobs-Reitsma et al. 1994; Van de Giessen et al. 1996; Jacobs-Reitsma 1997; Refregier-Petton et al. 2001; Bouwk- negt et al. 2004). These include, for example, poor farm hygiene, short time between two consecutive-production periods, the presence of other farm animals, rodents and insects, seasonal variations and partial depopulation. Although biosecurity measures, such as hygienic barriers and rodent control, have resulted in a decreased coloniza- tion of Campylobacter on broiler farms (Gibbens et al. 2001), infections on broiler farms still occur frequently Correspondence to: A. Bouma, Department of Farm Animal Health, Faculty of Veterinary Medicine, Utrecht University, Yalelaan 7, 3584 CL Utrecht, the Netherlands (e-mail: a.bouma@vet.uu.nl). Present address: A.D. Russa, Department of Anatomy and Histology, Muhimbili University College of Health Sciences, Dar es Salaam, Tanzania. ª 2005 The Society for Applied Microbiology Letters in Applied Microbiology 2005, 41, 280–285 doi:10.1111/j.1472-765X.2005.01751.x