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This research project aims to determine the relative contribution of different risk factors, both food and non-food related, to the burden of C. jejuni infection in humans.
Study Duration : April 2003 to April 2005
Contractor : Public Health Laboratory Service
Campylobacter is the most commonly reported cause of bacterial infectious intestinal disease (IID) in the UK. A wide range of risk factors for infection have been identified however a proportion of infections appear to be unexplained by recognised exposures. This suggests that numerous risk factors may be involved and/or that they may be due to as yet unidentified risk factors. The aim of this study was to determine the relative proportional contribution if different risk factors, both food and non-food related, to the burden of UK-acquired sporadic Campylobacter jejuni IID.
A case-control study was performed between 1 April 2005 and 30 June 2006 in five Health Protection Units (HPU) in England. Data were collected by means of a standard, self-administered questionnaire. Strains of Campylobacter isolated during the study period were submitted to HPA, where they were speciated and underwent antibiotic resistance determination. A sub-sample of isolates were also submitted for comparative phylogenomics (comparing genomes of different strains) and multilocus sequence typing (MLST).
Cases were defined as individuals aged 18 years or above with laboratory-confirmed Campylobacter spp. infection, reported to the HPUs involved in the study and registered with a GP in that area. Cases were excluded if they had travelled abroad 14 days prior to illness onset, or if they reported suffering from chronic gastrointestinal symptoms. Controls were frequency-matched to cases.
Odds ratios (OR), 95% confidence intervals (CI) and p-values were calculated to compare the prevalence of each exposure amongst cases and controls. Single and multivariable analyses were conducted.
In the comparative phylogenomics study whole genome comparisons were carried out and the relationship of strains examined using Bayesian-based algorithms. The isolates were also examined by MLST and a data tree was generated using ClonalFrame to infer clonal relatedness.
To read the final report click (External)
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Results from the case-control study, comparative phylogenomics and MLST studies suggest that chicken-related exposures, particularly the consumption of chicken, is a risk factor for a substantial proportion of human Campylobacter infections. None of the environmental exposures examined in the case-control study were associated with human illness.
In the single risk variable analysis factors associated with increased risk of Campylobacter enteritis were: self-reported diarrheal illness in the previous 12 months, self-reported previous Campylobacter enteritis, use of antibiotics, antacids and H2-receptor antagonists or proton pump inhibitors in the previous 28 days, owning a pet puppy, acquiring a pet dog 2 weeks to 3 months previously, consumption of chicken at least once weekly, consumption of red meat once a week, and sharing kitchen facilities.
In the final multivariable model consumption of chicken from a commercial establishment in the previous 5 days was a major risk factor (OR=1.95) as was consumption of chicken 4 or 5 times a week. Chicken prepared outside the home in the previous 5 days always carried a greater risk of illness than chicken prepared in the home. Other risk factors identified were self-reported previous Campylobacter enteritis (OR=2.2), use of H2-receptor antagonists or proton pump inhibitors (OR=3.4) and recent acquisition of a pet dog (OR=14.4). Identified risk factors accounted for 49% of cases; and chicken-related exposures accounted for 41% of cases.
The 158 Campylobacter jejuni strains examined by comparative phylogenomics fell into 2 clades; 81 isolates were associated with livestock strains (clade A) and 77 with non-livestock strains (clade B). MLST data were generated for 124 isolates that had undergone comparative phylogenomics and 257 isolates supplied by the HPA. Clonal complexes ST-21, ST-206 and ST-353 formed the bulk of clade A isolates, whereas clade B contained few isolates with ST-21 and ST-206 clonal complexes.
Clonal complex distribution of C.jejuni human isolates were compared with isolates from chicken and ruminants. The clonal complexes that were identified in chicken but not in bovids were present in human disease, whereas those rare in chicken were also rare in human disease.
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