A Risk Assessment of Shiga Toxin-producing Escherichia coli (STEC) in the Norwegian Meat Chain with Emphasis on Dry-cured Sausages

Abstract

coli is part of the normal gastrointestinal microbial flora of humans and animals. E. coli bacteria causing enteric/diarrhoeal disease are categorized into different groups based on their virulence properties and pathogenic features in humans. Enterohaemorrhagic E. coli (EHEC) are E. coli strains that  cause bloody diarrhoea  and haemolytic uraemic  syndrome  (HUS)  in humans, and have a defined zoonotic association. The major virulence factor of EHEC (and the actual  cause  of HUS)  is  the  ability  to  produce Shiga  toxins  (Stx),  thus  the  name Shiga Toxin Producing E. coli (STEC).  With enteropathogenic Escherichia  coli  (EPEC),  the diarrhoea in these  patients  is  due  to  attaching  and  effacing  (A/E)  lesions  in  the  enteric epithelium.    This risk assessment  was  conducted  after  a  human  outbreak  of  STEC  O103  in  2006, associated with contaminated dry-fermented sausages.   The Norwegian Scientific Committee for Food Safety (Vitenskapskomitéen for mattrygghet), Panel on  Biological  Hazards,  was  asked  by  the  Norwegian  Food  Safety  Authority (Mattilsynet) for  a  risk  assessment  regarding  shiga  toxin-producing  E.  coli  (STEC)  in  the Norwegian meat chain, with emphasis on dry-cured sausages. In response, an ad hoc Working Group  of  experts was  appointed with  the mandate  to  draft  a  risk  assessment  regarding  this issue.   The current report approaches the task by following and analysing the entire process, from the origin of the meats at farm level, to the final production and storage of dry-cured sausages. An overall  aim of  the  report has been  to  identify  and describe potential  intervention options  in various parts of this chain.     The main conclusions from the risk assessment are as follows:   It is  not  possible  to  give  any  reliable  quantitative  estimates  of  the  current  risk associated with consumption of dry-cured sausages.    There are  no  clear  indications  of  any  general  change  in  the  epidemiology  of  STEC  infections in humans in Norway over the last decade.   There is no documentation that there has been any change in the occurrence of various STEC in the domestic animal reservoir during the last decade.   The combination of proper slaughter hygiene and use of  thermal decontamination of sheep,  cattle  and  pig  carcasses  represents  an  efficient  way  to  reduce  STEC contamination. This approach would not only cause a reduction in the contamination level of STEC, but also provide a general beneficial effect on the level of other enteric pathogens, such as Salmonella and Yersinia enterocolitica.   Proper use  of  starter  cultures  in  fermentation,  combined  with  higher  fermentation temperatures,  will  reduce  the  probability  of  growth  of  STEC  in  contaminated  drycured sausages.   A combination  of  higher  fermentation  temperatures,  a  lower  pH  during  the  process, and heat-treatment of  the  final product should effectively eliminate  the potential  risk for transmission of STEC infections from consumption of dry-cured sausages. A 5 log reduction is possible.   Technological options  are  available  to  reduce  significantly  the  transfer  of  potential pathogens through meats in general, and specifically through dry-cured sausages.    The most important data gap is the lack of information about the actual occurrence of STEC infections  in  humans  in Norway.  Improved  laboratory  diagnostic  procedures and  epidemiological  surveillance,  combined with  better  reporting  and  tracing  in  the health care system are necessary.    The implementation  of  properly  designed  base-line  studies  of  various  domestic animals,  to  provide  data  on  the  occurrence  of  various  serotypes  and  their  virulence factors  present  is  recommended.  Also,  this  would  provide  a  better  basis  for comparison with human isolates.