Purpose: This study seeks to determine the current sources of human campylobacteriosis in Scotland.
Methods: All clinical isolates (798) were collected over the twelve month period to March 2011 along with epidemiological data (isolation date, patient gender, age and home address, exposure and foreign travel information). Campylobacter isolates from the principal source hosts were also collected: retail chicken (238), cattle (142) and sheep (167). Multi-locus Sequence Typing at ten loci (seven housekeeping, porA, flaA, flaB) was carried out. Strain similarity was determined using Nei genetic distance and molecular attribution of source species using modeling by simple proportions (e.g., the Dutch model) and Bayesian stochastic methods (e.g., STRUCTURE and Asymmetric Island (AI) Model). Comparison was made to our large 2005/06 study.
Results: The study showed that there was a significant (P < 0.05) increase in prevalence from cattle (21.9% to 33.1%), sheep (33.2 – 52.7%) and retail chicken (64.0-90.3%). Nei’s genetic distance showed significant differences (P < 0.05) for all animal sources and humans between 2005-6 and 2011. Eight of the top 16 sequence types from clinical isolates changed in abundance between 2005-6 and 2011. Attribution to source in 2011 had the same rank order as previously with chicken most important followed by cattle and sheep, then wild birds and pigs. There was a difference between the source attribution models for attribution to chicken with the Asymmetric Island model attributing approximately 75-81% whilst STRUCTURE attributed 40-54%.
Significance: The findings indicate an increase in the prevalence in the ruminant and retail chicken sources as well as a change in the distribution (and relative importance) of different source and clinical sequence types. Source attribution indicates that retail chicken remains the most important source of human infection.