Campylobacter jejuni: exposure assessment and hazard characterization : growth, survival and infectivity of Campylobacter jejuni

Campylobacter jejuni, a small, curved or spirally shaped highly motile microorganism, is identified as a major cause of bacterial gastroenteritis throughout the world. Serious complications such as the Guillain-Barré syndrome and reactive arthritis might occasionally follow infection. In this thesis data were generated in the fields of hazard characterization and exposure assessment, which were used to identify risk factors for Campylobacter. Although C. jejuni is generally seen as an obligate micro-aerophile, in this thesis it was shown that it can grow aerobically in the presence of pyruvate, and growth might also be possible in the presence of other antioxidants. However, as result of the strict minimal growth temperature (30ºC), C. jejuni is still assumed to be generally unable to grow in foods and therefore growth is not considered as a large risk for campylobacteriosis. C. jejunican, and does, survive effectively for long periods of time under non-growing conditions in various environments. Temperature is the most influencing factor in survival and survival will be optimal at low temperatures (around 4ºC). As many foods are stored chilled, this will prolong the survival of C. jejuni. Furthermore survival is enhanced at low oxygen conditions, as often present in packaged foods. While the effects of environmental conditions on the survival of C. jejuni have been studied extensively, the knowledge of the effect of environmental factors on the infectivity was scarce. Therefore, the effect of environmental conditions (temperature, medium and atmosphere) on both the survival of C. jejuni and the infectivity of the surviving cells was investigated. We revealed that culturability and infectivity are linearly related. Furthermore, our study on the effect on the infectivity of adding nonculturable C. jejuni cells to culturable cell suspensions, showed nonculturable cells not to be infective (in vitro). Therefore, absence of culturable C. jejuni cells indicates that a product can be regarded as representing a very low risk with respect to campylobacteriosis. Food products can be contaminated with Campylobacter during production or afterwards at the consumer’s home. Once contaminated the risk is high that Campylobacter will survive on food products until the moment of consumption, except if the product undergoes an elimination step during preparation, such as heating. The growth requirements for Campylobacter are met in the gastrointestinal tract of warm-blooded animals. As a result especially products of animal origin, like chicken meat and raw milk, are often contaminated by Campylobacter, but also products of non-animal origin, like vegetables and fruits, can be contaminated. Within the exposure assessment cross-contamination in the home, the importance of raw vegetables and fruits as a risk factor for Campylobacter, and the relative importance of chicken meat, raw milk and raw vegetables and fruits were studied. The effect of different cross-contamination routes during the preparation of a chicken fruit salad was investigated. It was shown that the mean transfer rate by cross-contamination was 0.12% of the initial number of C. jejunion the chicken fillet, and that the different tested cross-contamination routes; cutlery, cutting board and hands, were equally important. The high prevalence and concentration of C. jejuni on chicken meat, the high percentage of consumers who exhibit improper hygienic and cleaning behaviour, and the significant transfer of Campylobacter during improper food preparation, indicate cross-contamination from raw foods, such as chicken, to other ready-to-eat foods as a large risk factor for Campylobacter infection. Fresh produce can become contaminated with C. jejuni during cultivation or processing. Especially vegetables and fruits which are eaten raw may present a risk. In this thesis Dutch data on the prevalence of Campylobacter on raw vegetables and fruits were newly analysed. Thirteen of the 5640 vegetable and fruit samples were Campylobacter positive, resulting in a prevalence of 0.23% (95% confidence interval (Cl): 0.12-0.39%). The prevalence on packaged products was significantly higher than on unpackaged products. Finally, the newly acquired data and quantitative literature data on the prevalence and concentration of Campylobacter entering the consumer phase were summarized for three food groups; vegetables and fruit, chicken, and raw milk. These data were used in a quantitative risk assessment model to estimate the exposure and the number of illnesses as result of the consumption of these foods and to compare their relative importance. The prevalence and concentration are low on raw vegetables and fruit, but the quantity of raw vegetables and fruits consumed is very high. In contrast, raw chicken and raw milk show relative high prevalence and concentration levels, but the consumption is low. Despite the differences in parameters, the exposure calculated out of the combination of parameters indicates all these three foods as high risk factors for Campylobacter. So foods which are not heavily contaminated with Campylobacter, but are consumed in large quantities can constitute a similar high risk on Campylobacter infection as foods which are consumed in small quantities but are heavily contaminated with Campylobacter.