[1] Univ Ghent, Fac Vet Med, Dept Reprod Obstet & Herd Hlth, Vet Epidemiol Unit, Salisburylaan 133, B-9820 Merelbeke, Belgium
[2] Univ Ghent, Fac Vet Med, Dept Vet Publ Hlth & Food Safety, B-9820 Merelbeke, Belgium
[3] Coordinat Ctr Vet Diagnost, Vet & Agrochem Res Ctr, CERVA, CODA, B-1180 Uccle, Belgium
[4] Sci Inst Publ Hlth, Dept Epidemiol, B-1050 Brussels, Belgium
[5] Univ Liege, Dept Food Sci, Fac Vet Med, Microbiol Sect, B-4000 Liege, Belgium
[6] ILVO, Inst Agr & Fisheries Res, B-9090 Melle, Belgium