Infectious Diseases 2018

Infectious Diseases 2018

Campylobacter in Scotland

17 February, 2018

The University of Aberdeen compared clinical strains of the pathogen from the Grampian area with strains isolated from chickens, cattle, sheep, pigs and wild birds. Campylobacter isolates were collected from clinical cases from Apr 2015 to Dec 2016 along with those from abattoir sampled whole birds (representing retail ready chicken) and caecal samples (representing the farm environment). Different strains were identified from the isolates obtained and molecular attribution models were used to attribute clinical isolates to specific host reservoirs. The information obtained from a questionnaire sent to all human cases allowed greater understanding of the exposures, routes of infection, seasonal trends and the risk factors associated with human campylobacteriosis in Grampian. Sensitivity analyses were performed in order to test the robustness of attribution models used. Molecular phylogeny methods (family trees) were used to detect case clustering of subtypes of Campylobacter in order to establish whether a direct link between cases and sources might be discernible. 
The Findings
The chicken strains from Grampian supermarkets and the studied Scottish abattoirs had some overlap with high carriage of Campylobacter on both whole birds and from farms. All of the abundant strains found in whole birds at the abattoir and caeca were also commonly found in human cases. Around half of the flocks were treated with at least one antibacterial agent. As observed in the previous study, the strains from chickens were most common in humans, followed by those from ruminant (cattle and sheep) sources. The proportion of cases attributed to chicken decreased from 55-75% to 52-68% when compared to data from 2012-2015. Other sources of infection are 14-26% for sheep, 9-11% for cattle, 1-2% for pigs and 7-8% for wild birds.
The Conclusions
- Virtually all broiler farms were positive for Campylobacter indicating more needs to be done on-farm in order to minimise risk of human campylobacteriosis.
- 21% of the caecal strains (representative of farm environment) were different to the strains from that flock’s whole birds, suggesting multiple strain colonisation on the farm or cross contamination between the flocks during processing in the abattoir.
- More than half of the paired bird samples had the same strain with one or both whole bird isolates being the same as the caecal isolate, implying predominant strain colonisation at the farm level.
- Half of the flocks were treated with at least one antimicrobial agent, which can lead to emergence of resistant strains and their persistence in the poultry chain or the farm environment.
- There was commonality of strains from chickens and human cases which indicates strong evidence of a link between these. SNP types were found which were identical between chicken and human isolates further strengthening this link.
- The recent fall in human cases appears not to be due solely to a fall in Campylobacter cases attributable to chicken.

Related Links
Link The full study