[1] Natl Inst Publ Hlth & Environm, Ctr Infect Dis Control Netherlands, NL-3720 BA Bilthoven, Netherlands
[2] Univ Utrecht, Div Vet Publ Hlth, Inst Risk Assessment Sci, NL-3508 TD Utrecht, Netherlands
[3] Free Univ Amsterdam, Med Ctr, Dept Med Microbiol & Infect Control, NL-1007 MB Amsterdam, Netherlands
[4] Univ Utrecht, Fac Vet Med, Dept Infect Dis & Immunol, NL-3508 TD Utrecht, Netherlands
[5] Univ Gottingen, Inst Med Microbiol, D-37075 Gottingen, Germany
[6] Vet Labs Agcy, Addlestone KT15 3NB, Surrey, England
[7] Cent Vet Inst, NL-8200 AB Lelystad, Netherlands