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Applied and Environmental Microbiology, October 2009, p. 6361-6366, Vol. 75, No. 19
0099-2240/09/$08.00+0     doi:10.1128/AEM.00961-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Quantification of Horizontal Transmission of Salmonella enterica Serovar Enteritidis Bacteria in Pair-Housed Groups of Laying Hens{triangledown} ,{dagger}

M. E. Thomas,1 D. Klinkenberg,2 G. Ejeta,2,{ddagger} F. Van Knapen,1 A. A. Bergwerff,1 J. A. Stegeman,2 and A. Bouma2*

Veterinary Public Health Division, Institute for Risk Assessment Sciences, Utrecht University, Yalelaan 2, 3584 CM Utrecht, The Netherlands,1 Department of Farm Animal Health, Faculty of Veterinary Medicine, Utrecht University, Yalelaan 7, 3584 CL Utrecht, The Netherlands2

Received 28 April 2009/ Accepted 2 August 2009

An important source of human salmonellosis is the consumption of table eggs contaminated with Salmonella enterica serovar Enteritidis. Optimization of the various surveillance programs currently implemented to reduce human exposure requires knowledge of the dynamics of S. Enteritidis infection within flocks. The aim of this study was to provide parameter estimates for a transmission model of S. Enteritidis in laying-type chicken flocks. An experiment was carried out with 60 pairs of laying hens. Per pair, one hen was inoculated with S. Enteritidis and the other was contact exposed. After inoculation, cloacal swab samples from all hens were collected over 18 days and tested for the presence of S. Enteritidis. On the basis of this test, it was determined if and when each contact-exposed hen became colonized. A transmission model including a latency period of 1 day and a slowly declining infectivity level was fitted. The mean initial transmission rate was estimated to be 0.47 (95% confidence interval [CI], 0.30 to 0.72) per day. The reproduction number R0, the average number of hens infected by one colonized hen in a susceptible population, was estimated to be 2.8 (95% CI, 1.9 to 4.2). The generation time, the average time between colonization of a "primary" hen and colonization of contact-exposed hens, was estimated to be 7.0 days (95% CI, 5.0 to 11.6 days). Simulations using these parameters showed that a flock of 20,000 hens would reach a maximum colonization level of 92% within 80 days after colonization of the first hen. These results can be used, for example, to evaluate the effectiveness of control and surveillance programs and to optimize these programs in a cost-benefit analysis.

* Corresponding author. Mailing address: Department of Farm Animal Health, Faculty of Veterinary Medicine, Utrecht University, Yalelaan 7, 3584 CL Utrecht, The Netherlands. Phone: (31) 30-2531248. Fax: (31) 30-2521887. E-mail: a.bouma{at}uu.nl

{triangledown} Published ahead of print on 7 August 2009.

{dagger} Supplemental material for this article may be found at http://aem.asm.org/.

{ddagger} Present address: Department of Microbiology and Veterinary Public Health, Faculty of Veterinary Medicine, Addis Ababa University, P.O. Box 34, Bishoftu, Ethiopia.

Applied and Environmental Microbiology, October 2009, p. 6361-6366, Vol. 75, No. 19
0099-2240/09/$08.00+0     doi:10.1128/AEM.00961-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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