Molecular epidemiology of Campylobacter jejuni in a geographically isolated country with a uniquely structured poultry industry

Abstract

In New Zealand the number of campylobacteriosis notifications increased markedly between 2000 and 2007. Notably, this country's poultry supply is different than that of many developed countries as the fresh and frozen poultry available at retail are exclusively of domestic origin. To examine the possible link between human cases and poultry, a sentinel surveillance site was established to study the molecular epidemiology of Campylobacter jejuni over a 3-year period from 2005 to 2008 using multilocus sequence typing. Studies showed that 60.1 to 81.4% of retail poultry carcasses from the major suppliers were contaminated with C. jejuni. Differences were detected in the probability and level of contamination and the relative frequency of genotypes for individual poultry suppliers and humans. Some carcasses were contaminated with isolates belonging to more than one sequence type (ST), and there was evidence of both ubiquitous and supplier-associated strains, an epidemiological pattern not recognized yet in other countries. The common poultry STs were also common in human clinical cases, providing evidence that poultry is a major contributor to human infection. Both internationally rare genotypes, such as ST-3069 and ST-474, and common genotypes, such as ST-45 and ST-48, were identified in this study. The dominant human sequence type in New Zealand, ST-474, was found almost exclusively in isolates from one poultry supplier, which provided evidence that C. jejuni has a distinctive molecular epidemiology in this country. These results may be due in part to New Zealand's geographical isolation and its uniquely structured poultry industry.

FIG. 1.

Probabilities of Campylobacter contamination on poultry carcasses for each supplier for different quarters.

FIG. 2.

Levels of Campylobacter contamination on positive poultry carcasses for each supplier for different quarters.

FIG. 3.

Relative frequencies of the three major human C. jejuni MLST genotypes in clinical cases from the MidCentral District surveillance site, New Zealand, in each quarter between March 2005 and February 2008.

FIG. 4.

Population structure of C. jejuni for different poultry suppliers estimated by cluster analysis using Structure 2.2. The posterior probabilities that each isolate belongs to cluster 1 (light gray), cluster 2 (white), and cluster 3 (dark gray) are shown. Isolates are grouped by supplier and ordered by ST.