Risk assessment of verocytoxin-producing E. coli (VTEC) in Danish pork

Abstract

Verocytotoxin-producing Escherichia coli (VTEC) is recognized as a food-borne pathogen of major importance. Infection by VTEC is known to cause a wide range of symptoms, from uncomplicated diarrhoea to haemorrhagic colitis, haemolytic uraemic syndrome and death. VTEC has primarily been isolated from cattle. However, in several countries VTEC has also been isolated from pigs. The prevalence in Danish pigs remains unknown but a small-scale study indicated that is was very low (2.1%) (non-published). All isolates were VTEC types that very rarely have been associated with human disease and are considered low pathogenic VTEC. The present risk assessment aimed at assessing whether human cases of VTEC could be attributed to Danish pigs and pork. A review of recent studies on VTEC gave no indication that VTEC in Danish pork should be considered a risk to the consumers. Introduction VTEC is an emerging zoonotic pathogen causing severe illness in humans. The main sources of human exposure to VTEC have been considered to be contaminated bovine products but several other sources have been identified. At present, pigs and pork are not considered to be the source of human VTEC infections in Denmark. However, VTEC has been reported in pigs and pork in several countries and therefore, it cannot be ruled out that pork could be a source of VTEC infection in humans. The present risk assessment was carried out to assess whether human cases of VTEC could be attributed to Danish pigs and pork. Materials and Methods The structure in the Codex Alimentarius guideline for risk assessment was adopted—including hazard identification, hazard characterization, exposure assessment and risk characterization. The hazard identification and characterization covered a description of the agent and its virulence and pathogenicity. A description of the range and severity of clinical manifestations of the infection in humans was also included. In the exposure assessment, both cattle and pigs were considered but the primary focus was on pigs and pork. The exposure assessment covered: < the origin of the meat consumed in Denmark; < the prevalence of VTEC in live animals, and in raw meat and meat products in several countries; < the growth in meat and processed meat and factors influencing it; < the consumption of meat and meat products in Denmark. However, the prevalence data was insufficient and incomplete. Especially, information about the prevalence of VTEC in Danish pigs and pork was sparse. Data about the consumption of meat and meat products was also poor, in particular for children below 5 years of age. Considering that children in this age group appear to be highly susceptible, this constituted a serious problem in the risk quantification step of the risk characterization. For these reasons, we decided to abandon the quantitative risk assessment approach and instead carry out a qualitative risk assessment. Expert opinion was used to increase the applicability of the incomplete data. Results Hazard identification VTEC is a food-borne pathogen of major importance. This was realized for the first time in 1982 in connection with two outbreaks of haemorrhagic colitis (HC) in the states of Oregon and Michigan, USA (Riley et al., 1983). Since then, several human out-breaks have been reported throughout the world. In Denmark, human cases of VTEC infection have been reported since 1997, when molecular detection methods were introduced. VTEC is now the 5 most frequent cause of gastrointestinal infection in humans and more common than Shigella infection (Scheutz et al., 2005). Since 1997, there appears to be an increase in the National incidence (3.1 per 100.000 per year in 2004) (Scheutz et al., 2005) but this may partly be explained by an overall increase in sen-