Human Campylobacteriosis in Luxembourg, 2010-2013: A Case-Control Study Combined with Multilocus Sequence Typing for Source Attribution and Risk Factor Analysis

Abstract

Campylobacteriosis has increased markedly in Luxembourg during recent years. We sought to determine which Campylobacter genotypes infect humans, where they may originate from, and how they may infect humans. Multilocus sequence typing was performed on 1153 Campylobacter jejuni and 136 C. coli human strains to be attributed to three putative animal reservoirs (poultry, ruminants, pigs) and to environmental water using the asymmetric island model. A nationwide case-control study (2010-2013) for domestic campylobacteriosis was also conducted, including 367 C. jejuni and 48 C. coli cases, and 624 controls. Risk factors were investigated by Campylobacter species, and for strains attributed to different sources using a combined case-control and source attribution analysis. 282 sequence types (STs) were identified: ST-21, ST-48, ST-572, ST-50 and ST-257 were prevailing. Most cases were attributed to poultry (61.2%) and ruminants (33.3%). Consuming chicken outside the home was the dominant risk factor for both Campylobacter species. Newly identified risk factors included contact with garden soil for either species, and consuming beef specifically for C. coli. Poultry-associated campylobacteriosis was linked to poultry consumption in wintertime, and ruminant-associated campylobacteriosis to tap-water provider type. Besides confirming chicken as campylobacteriosis primary source, additional evidence was found for other reservoirs and transmission routes.

Figure 1. Human Campylobacter sequence types and clonal complexes.

The category ‘others’ includes sequence types with ≤5 isolates and clonal complexes with ≤3 isolates. White segments refer to C. jejuni, grey segments to C. coli.

Figure 2. Percentage of human C. jejuni (n = 1152) and C. coli (n = 136) cases attributed to poultry, ruminants, swine, and environmental water.

Error bars represent 95% confidence intervals.

Figure 3. Estimated source probability matrix plot for C. jejuni and C. coli.

Each human case is a vertical column with level of shading according to the probability that it originated from each of the sources. To aid visualization, cases are ordered horizontally according to the chicken source probability.

Figure 4. Migration and mutation rates of the different sources.

The pie charts show the probability that a newly sampled allele is a novel mutant (black segment) or identical to one already observed in the same or another source (segment coloured according to the colour of the source name).