Campylobacter Control Measures

“PulseNet is a network of public health laboratories that do molecular subtyping of foodborne bacteria from ill people across the country, to find and help investigate groups of related infection that may be the beginning of an outbreak,” Dr. Tauxe points out. “Using WGS for Listeria, we found more outbreaks than ever, traced them to new and unsuspected sources, and found new points where prevention can be improved. We are anticipating that the same thing can happen with Campylobacter and other foodborne bacteria, as we apply WGS methods for public health surveillance.”

That’s a good thing, Dr. Tauxe believes, since Campylobacter can cause more than severe bloody diarrhea. “In some people, it can be followed by longer lasting intestinal disturbances, and in a few, to a paralytic condition called the Guillain-Barré syndrome that can put people into intensive care for several weeks,” he notes.

Ann-Katrin Llarena, DVM, PhD, a researcher with the Department of Food Hygiene and Environmental Health, Faculty of Veterinary Medicine, University of Helsinki, Finland, believes WGS is set to emerge as the typing method of choice for Campylobacter jejuni (C. jejuni) outbreak investigations worldwide, and it has the potential for implementation in routine surveillance.

“However, several issues regarding epidemiology and genomic diversity need to be addressed before WGS can become a useful and reliable working tool in the public health sector response to campylobacteriosis,” Dr. Llarena says.

In a peer-reviewed article titled “Whole-Genome Sequencing in Epidemiology of Campylobacter jejuni Infections,” published in the May 2017 issue of the Journal of Clinical Microbiology, Dr. Llarena and her co-authors point out that, even though C. jejuni is one of the most frequent causes of bacterial gastroenteritis globally, the epidemiology of this pathogen is only partially understood, and shedding new light on this area is difficult, since most cases are sporadic and go unreported.

“Additionally, the possibility of immunity in the population, coupled with many different reservoirs, transmission pathways, and regional epidemiological differences, make source tracing and risk assessment of campylobacteriosis challenging,” Dr. Llarena notes.

“In particular, understanding the baseline ecological diversity and population structure of C. jejuni and the genomic diversity within a single human infection is necessary for defining interpretation criteria for determining whether isolates are likely to be clonal, as would be expected in a cluster of cases or an outbreak with a common source,” she continues.

Dr. Llarena explains that the presence of clonal populations, which are a population of bacteria with indistinguishable DNA descended from a common ancestor, makes genomic distinction between epidemiologically associated from nonrelated isolates difficult and can adversely affect the use of WGS methodology in C. jejuni surveillance and outbreak investigations for public health purposes.

“More studies exploring the genomic diversity and possible occurrence of clonal subpopulations in other C. jejuni lineages are needed to resolve this predicament,” she says.

In the plus column, Dr. Llarena relates, several studies have aimed to investigate the applicability of WGS analysis in identifying clonal C. jejuni isolates in point-source outbreaks, and the retrospective examination of foodborne and waterborne outbreaks of campylobacteriosis has gained significant research attention.

“In the absence of comprehensive and systematic surveillance, the detection of diffuse C. jejuni outbreaks, which are individual cases over a wide geographical area, is difficult, as these cases are masked against the background of sporadic cases,” Dr. Llarena says. “Earlier studies verified the existence of diffuse outbreaks of campylobacteriosis by demonstrating the presence of temporal, spatial, and genotypic clusters among apparently sporadic cases. Such clusters were several times more common than point-source outbreaks.”

High-resolution genotyping can improve the detection of clusters with diffuse epidemiological signals, Dr. Llarena mentions. “Since WGS offers the highest possible discriminatory power, the integration of genome sequencing in C. jejuni surveillance would be expected to facilitate the identification of possible case clusters, which should allow for the implementation of more effective intervention strategies targeted at the prevention and control of cases of campylobacteriosis,” she explains.