Surveillance of zoonotic bacteria in farm animals in The Netherlands. Results from January 1998 until December 2000

To obtain reliable quantitative data on the occurrence of zoonotic bacteria in farm animals in The Netherlands, a surveillance programme was implemented in April 1997. Results for January 1998 through December 2000 are presented in this report. In this period, faecal samples from in total 2,378 flocks/herds of layers, broilers, finishing pigs, dairy cattle and veal calves were examined for the presence of Salmonella spp., Campylobacter spp. and/or verocytotoxin-producing E. coli O157. Questionnaires were used to obtain data for risk factor analyses. For layers, prevalences of salmonella positive flocks were 12% (1998, using Rappaport-Vassiliadis (RV) as selective enrichment medium) and averaged around 20% in 1999 and 2000 (using both RV and modified semisolid RV (MSRV)); for broilers, the salmonella prevalence declined from 28% (1998, RV) to 16% (2000, RV & MSRV). For finishing pig, 34% (1998; 4th quarter only), 13% (1999) and 16% (2000) positive herds were identified, while for dairy cattle and veal calves, salmonella prevalences were around 3% (based on the use of RV only). Serotype discrimination showed the predominance of S. Enteritidis (mainly phagetype PT4) in layers in all years; for broilers this serotype prevailed until 1999, whereas S. Paratyphi B var. Java prevailed in 2000. In finishing pigs, S. Typhimurium predominated, with an increase of phagetype DT104 during the study period. The campylobacter prevalence in broilers decreased from 31% (1998) to 18% (1999), reaching 24% in 2000. Finishing pigs, dairy cattle and veal calves showed lower campylobacter prevalences for 1999 compared to 1998. C. jejuni was the dominating species in broilers and dairy cattle, whereas C. coli predominated in pigs; both species prevailed equally in veal calves. Prevalence estimates for E. coli O157 in dairy cattle were 5% (1998), 8% (1999) and 6% (2000; 8% with an adjusted processing of samples); for veal calves these were 5% (1998), 9% (1999) and 11% (2000; 17% with the adjusted method). PCR-test results revealed the presence of the virulence associated SLT- and/or eae-genes in all isolates examined. Potential risk factors were identified for E. coli O157 in dairy cattle and for Campylobacter spp. in broilers