Date Published: May 8, 2019
Publisher: Public Library of Science
Author(s): Lisa M. Hodges, Catherine D. Carrillo, Jacqueline P. Upham, Antonela Borza, Mikaela Eisebraun, Robyn Kenwell, Steven K. Mutschall, David Haldane, Emily Schleihauf, Eduardo N. Taboada, Yung-Fu Chang.
Campylobacter is the leading cause of food-borne bacterial disease in Canada and many developed countries. One of the most common sources of human campylobacteriosis is considered to be the consumption or handling of raw or undercooked poultry. To date, few Canadian studies have investigated both the prevalence of Campylobacter on retail poultry and its potential impact on human clinical cases. The objective of this study was to evaluate the prevalence of Campylobacter spp. at the retail level and the correlation between subtypes recovered from chicken and those recovered from human clinical cases within the province of Nova Scotia, Canada. From this study 354 human clinical isolates were obtained from provincial hospital laboratories and a total of 480 packages of raw poultry cuts were sampled from retail outlets, yielding 312 isolates (65%), of all which were subtyped using comparative genomic fingerprinting (CGF). Of the 312 chicken isolates, the majority of isolates were C. jejuni (91.7%), followed by C. coli (7.7%) and C. lari (0.6%). Using CGF to subtype C. jejuni and C. coli isolates, 99 and 152 subtypes were recovered from chicken and clinical cases, respectively. The most prevalent human and chicken subtypes found in NS are similar to those observed nationally; indicating that the Campylobacter from this study appear to reflect of the profile of Campylobacter subtypes circulating nationally. Of the subtypes observed, only 36 subtypes were common between the two groups, however, these subtypes represented 48.3% of the clinical isolates collected. The findings from this study provides evidence that in Nova Scotia, retail poultry can act as a reservoir for Campylobacter subtypes that have been implicated in human illness.
Amongst developed countries, including Canada and the USA, Campylobacter spp. are one of the most common causes of food-borne bacterial gastroenteritis reported each year [1–3]. In Canada, 20,450 cases of campylobacteriosis were reported between 2012 and 2013, an average of approximately 28.5 cases/ 100,000 population (NDO). While campylobacteriosis is typically self-limiting, the severity of the illness can range from asymptomatic to severe enteritis. Typical symptoms include diarrhea, abdominal pain, fever, anorexia and headache, however, in some cases, infections can lead to hospitalizations, post-infection sequelae and death . In addition, infection by Campylobacter jejuni is also considered to be the most common antecedent infection of Guillan-Barré syndrome (GBS), an autoimmune disease resulting in paralysis and even death [2,5,6]. Other sequelae include reactive arthritis and inflammatory bowel disease . C. jejuni is isolated from the majority of human cases of campylobacteriosis (> 90% of cases), followed by C. coli and C. lari .
This study represents the largest sampling of Campylobacter on raw, retail poultry in Nova Scotia and amongst the largest of the Canadian studies to date [22,23,25,31,32]. Although several studies have previously examined prevalence of Campylobacter at the farm and abattoir level, very few studies actually report on the prevalence of Campylobacter on retail poultry. However, prevalence at the farm and abattoir level does not necessarily correlate to the level of risk to the final consumer since it does not reflect the primary point of exposure . This study found that 65% of the raw packaged chicken sold in Nova Scotia were contaminated with Campylobacter spp., consistent with some previously reported prevalence rates [33–35], in which 62% to 70% of raw retail chicken tested positive. In contrast, other Canadian studies have reported considerably lower prevalence rates of Campylobacter, ranging from 29% to 42.8% of the samples tested [22–24,36,37]. Excluding a subset of samples tested in two studies [22,23], none of these studies were conducted in Nova Scotia. The considerably lower prevalence rates of Campylobacter spp. reported by these studies may be largely due to differences in the methodology and sampling. The most notable differences between this study and others include that > 200 g samples were used, the type of enrichment broth, that no cycloheximide was added to the enrichment broth and that passive filtration was used to reduce the presence of competing background flora. These factors have been shown to affect the detection and isolation of Campylobacter [23,38,39]. The seasonality of this study (summer to early fall) is also likely to have resulted in increased recovery. Prevalence of Campylobacter is well known to increase in broiler chickens in the summer months [22,40,41]. The prevalence during the same time period in retail poultry analysed in the Canadian National Microbiological Study was 50%, indicating that methodology likely has a more important influence than seasonality . While the prevalence rates vary between studies, there is agreement between this study and previous Canadian studies that C. jejuni is the most frequently isolated species on poultry (> 80%), followed by C. coli and then C. lari.
The high degree of correlation between the Nova Scotia and Canadian prevalence rates and comparable abundance in subtype profiles provide evidence that this study conducted in Nova Scotia is reflective of the Campylobacter population circulating at the national level. While the commonality of a subtype between human clinical cases and chicken does not correlate directly to causation, it does provide evidence that retail chicken act as a significant source for Campylobacter subtypes known to be implicated in human infections in Nova Scotia. The application of whole-genome sequencing analysis to examine the molecular epidemiology of campylobacteriosis in Nova Scotia is likely to shed light on the direct link between C. jejuni strains circulating in poultry and those observed in human clinical cases . Future work should also focus on investigating factors (e.g. differences in virulence, ability to survive in the food production systems, or in their ability to colonize a range of hosts) that influence subtype prevalence in chickens and the degree of risk to humans.