Abstract
In the autumn of 1995 the first outbreaks of enterohemorrhagic Escherichia coli O157:H7 including ca 100 human cases were reported in Sweden. From outbreaks in other countries it is known that cattle may carry these bacteria and in many cases is the source of infection. Therefore, the present study was performed to survey the Swedish bovine population for the presence of verotoxin-producing E. coli (VTEC) of serotype O157:H7. Individual faecal samples were collected at the 16 main Swedish abattoirs from April 1996 to August 1997. Of 3071 faecal samples, VTEC O157 were found in 37 samples indicating a prevalence of 1.2% (CI95% 0.8–1.6). All 37 isolates carried genes encoding for verotoxin (VT1 and/or VT2), intimin, EHEC-haemolysin and flagellin H7 as determined by PCR. Another 3 strains were of serotype O157:H7 but did not produce verotoxins. The 37 VTEC O157:H7 strains were further characterised by phage typing and pulsed-field gel electrophoresis. The results clearly show that VTEC O157:H7 is established in the Swedish bovine population and indicate that the prevalence of cattle carrying VTEC O157:H7 is correlated to the overall geographical distribution of cattle in Sweden. Results of this study have formed the basis for specific measures recommended to Swedish cattle farmers, and furthermore, a permanent monitoring programme was launched for VTEC O157:H7 in Swedish cattle at slaughter.
Highlights
The first case of enterohemorrhagic colitis due to infection with verotoxin-producing Escherichia coli (VTEC) O157:H7 in Sweden was reported in 1988 (Sjöblad et al 1989)
The results from the present study show that VTEC O157:H7 is present in the Swedish cattle population at a prevalence of ca 1.2% (CI95% 0.8-1.6)
The prevalence of VTEC O157:H7positive healthy cattle is in the range of what has been reported (0.4%-15.7%) in other western countries where extended studies have been performed on faecal samples from animals at slaughter (Chapman et al 1997, Heuvelink et al 1998, Bonardi et al 1999, van Donkersgoed et al 1999, Pradel et al 2000, Johnsen et al 2001, Lahti et al 2001, Meyer-Broseta et al 2001, Paiba et al 2002, Tutenel et al 2002)
Summary
The first case of enterohemorrhagic colitis due to infection with verotoxin-producing Escherichia coli (VTEC) O157:H7 in Sweden was reported in 1988 (Sjöblad et al 1989). In 1995, 114 human cases of infection caused by VTEC O157:H7 were reported. In Sweden, infections with VTEC O157:H7 in humans have been compulsorily notifiable since January 1, 1996 (www.sva.se/pdf/ zoonosrapp2001.pdf). Other VTEC serotypes than O157:H7 are not notifiable, but may be an emerging problem in Sweden as in other European countries. The source of infection for verified human VTEC O157:H7 cases in Sweden has been determined only occasionally. In 1995 it was not known whether VTEC O157:H7 was present in the Swedish bovine population. A nationwide monitoring programme was initiated in April 1996 to survey the Swedish bovine population for the presence of VTEC O157:H7, and if found, to what extent. Isolates of VTEC O157:H7 were to be characterised by their virulence genes (vtx; vtx; eaeA and EHEC hlyA), phage typing and pulsed-field gel electrophoresis
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