Genetic attribution of bacterial genotypes has become a major tool in the investigation of the epidemiology of campylobacteriosis and has implicated retail chicken meat as the major source of human infection in several countries. To investigate the robustness of this approach to the provenance of the reference data sets used, a collection of 742 Campylobacter jejuni and 261 Campylobacter coli isolates obtained from United Kingdomsourced chicken meat was established and typed by multilocus sequence typing. Comparative analyses of the data with those from other isolates sourced from a variety of host animals and countries were undertaken by genetic attribution, genealogical, and population genetic approaches. The genotypes from the United Kingdom data set were highly diverse, yet structured into sequence types, clonal complexes, and genealogical groups very similar to those seen in chicken isolates from the Netherlands, the United States, and Senegal, but more distinct from isolates obtained from ruminant, swine, and wild bird sources. Assignment analyses consistently grouped isolates from different host animal sources regardless of geographical source; these associations were more robust than geographic associations across isolates from three continents. We conclude that, notwithstanding the high diversity of these pathogens, there is a strong signal of association of multilocus genotypes with particular hosts, which is greater than the geographic signal. These findings are consistent with local and international transmission of host-associated lineages among food animal species and provide a foundation for further improvements in genetic attribution.Members of the genus Campylobacter, specifically Campylobacter jejuni and Campylobacter coli, are major causes of human morbidity worldwide and are the most common bacterial cause of gastroenteritis in industrialized countries (4). These bacteria are commonly found as apparently harmless members of the gut microbiota of many farmed and wild mammals and birds. This, together with the sporadic nature of most human disease, has contributed to the remaining uncertainty regarding the relative importance of different potential sources of human infection (34), inhibiting the implementation of effective public health interventions, which may have major economic consequences on intensive food production. Human infection with C. jejuni and C. coli has been epidemiologically linked to contact with pets and farm animals and to consumption of red meat, water, milk, and poultry (17,20,34).The advent of multilocus sequence typing (MLST) for both C. jejuni and C. coli and its application to large and diverse isolate collections have enhanced understanding of the ecology (38) and epidemiology (10) of these important pathogens. It has been shown that there is substantial genetic differentiation between farmed ruminants and chickens (29) and even greater differentiation between farmed chickens and wild birds at the same farm site (5). Furthermore, MLST supports the application of popul...
Summary In recent years the importance of prepared salads as potential vehicles of gastrointestinal infection has been highlighted by several large outbreaks both nationally and across international boundaries. Between 1992 and 2006, 2274 foodborne general outbreaks of infectious intestinal disease were reported in England and Wales, of which 4% were associated with the consumption of prepared salads. In total, 3434 people were affected, with 66 hospitalizations and one death reported. The attribution of prepared salad types and pathogens among prepared salad associated outbreaks are presented and discussed. Findings from UK studies on salad vegetables, fruit and mixed salads from 1995 to 2007 (21 247 samples) indicate that most bacteria of concern with regard to human health are relatively rare in these products (98·6% of satisfactory quality); however, outbreaks of salmonellosis were uncovered associated with bagged salad leaves and fresh herbs during two such studies. Although it is known that fresh salad vegetables, herbs or fruit may become contaminated from environmental sources, only in recent years has the association of foods of nonanimal origin, such as salad vegetables, with foodborne illness become evident and recurrent, demonstrating that major health problems can arise from consumption of contaminated prepared salads if hygiene practices breakdown.
The increasing availability of bagged prepared salad vegetables reflects consumer demand for fresh, healthy, convenient, and additive-free foods that are safe and nutritious. During May and June 2001 a study of retail bagged prepared ready-to-eat salad vegetables was undertaken to determine the microbiological quality of these vegetables. Examination of the salad vegetables revealed that the vast majority (3,826 of 3,852 samples; 99.3%) were of satisfactory or acceptable microbiological quality according to Public Health Laboratory Service microbiological guidelines, while 20 (0.5%) samples were of unsatisfactory microbiological quality. Unsatisfactory quality was due to Escherichia coli and Listeria spp. (not Listeria monocytogenes) levels in excess of 10(2) CFU/g. However, six (0.2%) samples were of unacceptable microbiological quality because of the presence of Salmonella (Salmonella Newport PT33 [one sample], Salmonella Umbilo [three samples], and Salmonella Durban [one sample]) or because of a L. monocytogenes level of 660 CFU/g, which indicates a health risk. In each case, the retailer involved and the UK Food Standards Agency were immediately informed, and full investigations were undertaken. Nineteen cases of Salmonella Newport PT33 infection were subsequently identified throughout England and Wales. The outbreak strain of Salmonella Newport PT33 isolated from the salad and from humans had a unique plasmid profile. Campylobacter spp. and E. coli O157 were not detected in any of the samples examined. The presence of Salmonella, as well as high levels of L. monocytogenes, is unacceptable. However, minimally processed cut and packaged salad is exposed to a range of conditions during growth, harvest, preparation, and distribution, and it is possible that these conditions may increase the potential for microbial contamination, highlighting the necessity for the implementation of good hygiene practices from farm to fork to prevent contamination and/or bacterial growth in these salad products.
Systematic national surveillance of foodborne disease outbreaks effectively serves the development of public health policy on food safety. The Health Protection Agency has maintained a collaborative surveillance system for foodborne outbreaks in England and Wales since 1992. Up to 2008, 2429 foodborne outbreaks were identified, described and analysed for changes over time. Salmonella spp. accounted for half of the outbreaks, although the proportion of these decreased over the surveillance period. Similarly, the proportion of outbreaks caused by Clostridium perfringens decreased, while those attributed to Campylobacter spp. and Vero cytotoxin-producing Escherichia coli O157 increased. Although poultry meat was the most frequently implicated food vehicle in outbreaks followed by miscellaneous foods and red meats, the proportion of outbreaks attributed to meats in fact decreased over time but those linked to miscellaneous foods did not. Over the surveillance period, the proportion of outbreaks linked to eggs and S. Enteritidis non-phage-type 4, particularly in food service establishments, increased, highlighting the importance of this organism/setting/vehicle association. Contributory factors in most outbreaks were cross-contamination, inadequate heat treatment, and inappropriate food storage. This study describes the overall decline in foodborne outbreaks, providing evidence that the introduction and adherence to effective control measures provide the best means of minimizing the risk of foodborne infection.
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