Limitations of pulsed-field gel electrophoresis for the routine surveillance of Campylobacter infections

Ongoing Outbreak of Extensively Drug-Resistant Campylobacter jejuni Infections Associated With US Pet Store Puppies, 2016-2020

IMPORTANCE

Extensively drug-resistant Campylobacter jejuni infections cannot be treated with any commonly recommended antibiotics and pose an increasing public health threat.

OBJECTIVES

To investigate cases of extensively drug-resistant C jejuni associated with pet store puppies and describe the epidemiologic and laboratory characteristics of these infections.

DESIGN, SETTING, AND PARTICIPANTS

In August 2017, health officials identified, via survey, patients with C jejuni infections who reported contact with puppies sold by pet stores. In conjunction with state and federal partners, the Centers for Disease Control and Prevention investigated cases of culture-confirmed C jejuni infections in US patients with an epidemiologic or molecular association with pet store puppies between January 1, 2016, and February 29, 2020. Available records from cases occurring before 2016 with genetically related isolates were also obtained.

MAIN OUTCOMES AND MEASURES

Patients were interviewed about demographic characteristics, health outcomes, and dog exposure during the 7 days before illness onset. Core genome multilocus sequence typing was used to assess isolate relatedness, and genomes were screened for resistance determinants to predict antibiotic resistance. Isolates resistant to fluoroquinolones, macrolides, and 3 or more additional antibiotic classes were considered to be extensively drug resistant. Cases before 2016 were identified by screening all sequenced isolates submitted for surveillance using core genome multilocus sequence typing.

RESULTS

A total of 168 patients (median [interquartile range] age, 37 [19.5-51.0] years; 105 of 163 female [64%]) with an epidemiologic or molecular association with pet store puppies were studied. A total of 137 cases occurred from January 1, 2016, to February 29, 2020, with 31 additional cases dating back to 2011. Overall, 117 of 121 patients (97%) reported contact with a dog in the week before symptom onset, of whom 69 of 78 (88%) with additional information reported contact with a pet store puppy; 168 isolates (88%) were extensively drug resistant. Traceback investigation did not implicate any particular breeder, transporter, distributer, store, or chain.

CONCLUSIONS AND RELEVANCE

Strains of extensively drug-resistant C jejuni have been circulating since at least 2011 and are associated with illness among pet store customers, employees, and others who come into contact with pet store puppies. The results of this study suggest that practitioners should ask about puppy exposure when treating patients with Campylobacter infection, especially when they do not improve with routine antibiotics, and that the commercial dog industry should take action to help prevent the spread of extensively drug-resistant C jejuni from pet store puppies to people.

Prevalence, genotypic diversity and detection of virulence genes in thermotolerant Campylobacter at different stages of the poultry meat supply chain

Thermotolerant Campylobacter is the leading bacterial cause of foodborne illness in humans worldwide. The objectives of this study were to estimate prevalence and to identify and characterize potential sources of thermotolerant Campylobacter contamination in broilers on farms and at the slaughterhouse; to evaluate the clonal relationship among thermotolerant Campylobacter isolates from different stages of the broiler meat supply chain, and to analyze the presence of virulence genes in different sources of thermotolerant Campylobacter. A total of 1210 samples were collected from three broiler meat supply chains in Santa Fe, Argentina. At the farms, the sampling collection included broilers one week prior to slaughter, wild-living birds, domestic dogs, wild rodents, farm workers' boots, litter, feed, drinking water, flies, and darkling beetles (Alphitobius diaperinus). At the slaughtering line, the samples taken were from the evisceration zone (broiler cecum, working surfaces, evisceration knives and workers' hands), from the chiller zone (surfaces and direct supply water) and from the packing zone (work surfaces, workers' hands and broiler carcasses). The samples taken along each supply chain were in the same batch. The isolates obtained were identified to the species level (C. jejuni and C. coli) by multiplex PCR and were analyzed using pulsed-field gel electrophoresis to compare different profiles according to the source. Finally, the presence of 11 virulence genes was examined (cadF, cdtA, cdtB, cdtC, ciaB, flaA, flhA, iam, wlaN, virB11, racR). From 254 isolates, 128 (50.4%) were Campylobacter jejuni and 126 (49.6%) Campylobacter coli. C. jejuni was the species most prevalent in farm and C. coli the species most prevalent at the slaughterhouse. We detected thermotolerant Campylobacter in samples of wild birds, darkling beetles, farm workers' boots, flies and litter. At the slaughterhouse, the prevalence varied along the process line. By analyzing PFGE results, C. jejuni showed 21 profiles with three predominant genotypes, while C. coli showed 14 profiles with four predominant genotypes. A high genotype diversity was found; however, relationships between isolates from different stages of the broiler meat chain, between broiler and potential sources of thermotolerant Campylobacter contamination and between strains in the farm and in the slaughterhouse were detected. Furthermore, there was evidence of cross-contamination at the slaughterhouse. FlaA, flhA genes were detected in all strains, and the third most prevalent virulence gene was cadF. Only those strains obtained from flies, wild-living birds and broiler carcass samples harbored 10 of 11 pathogenic genes. The prevalence of some pathogenic genes between C. jejuni and C. coli was different. This evidence should contribute the scientific basis to implement risk management measures in public health.

Thermotolerant Campylobacter spp. in chicken and bovine meat in Italy: Prevalence, level of contamination and molecular characterization of isolates

Campylobacter species are common foodborne pathogens associated with cases of human gastroenteritis worldwide. A detailed understanding of the prevalence, contamination levels and molecular characteristics of Campylobacter spp. in cattle and chicken, which are likely the most important sources of human contamination, is imperative. A collection of 1243 poultry meat samples (665 chicken breasts and 578 chicken thighs) and 1203 bovine meat samples (689 hamburgers and 514 knife-cut meat preparations) were collected at retail outlets, in randomly selected supermarkets located in different Italian regions during one year. Of these samples, 17.38% of the poultry meat and 0.58% of the bovine meat samples tested positive for Campylobacter, of which 131 were Campylobacter jejuni (57.96%) and 95 were Campylobacter coli (42.03%). Campylobacter isolates were genotyped with the aim of assessing the genetic diversity, population structure, source distribution and Campylobacter transmission route to humans. All isolates were molecularly characterized by pulse field gel electrophoresis (PFGE), and further genotyped using multilocus sequence typing (MLST) and fla-SVR sequencing to gain better insight into the population structure. Antibiotic resistance was also investigate. The highest levels of resistance among chicken strains were observed for ciprofloxacin (88.25%), nalidixic acid (81.45%) and tetracycline (75.6%). PFGE analysis revealed 73 pulsotypes for C. jejuni and 54 pulsotypes for C. coli, demonstrating the existance of different and specific clones circulating in Italy. MLST of C.jejuni isolates mainly clustered in the CC353, CC354, CC21, CC206 and CC443; while C.coli isolates clustered only in CC828. The most common flaA alleles were 287 for C. jejuni and 66 for C. coli. Our study confirms that poultry meat is the main source of Campylobacteriosis, whereas red meat had a low level of contamination suggesting a minor role in transmission. The high presence of Campylobacter in retail chicken meat, paired with its increased resistance to antimicrobials with several multidrug resistance profiles detected, is alarming and represents a persistent threat to public health.

Differentiation of Campylobacter jejuni and Campylobacter coli Using Multiplex-PCR and High Resolution Melt Curve Analysis

Campylobacter spp. are important causes of bacterial gastroenteritis in humans in developed countries. Among Campylobacter spp. Campylobacter jejuni (C. jejuni) and C. coli are the most common causes of human infection. In this study, a multiplex PCR (mPCR) and high resolution melt (HRM) curve analysis were optimized for simultaneous detection and differentiation of C. jejuni and C. coli isolates. A segment of the hippuricase gene (hipO) of C. jejuni and putative aspartokinase (asp) gene of C. coli were amplified from 26 Campylobacter isolates and amplicons were subjected to HRM curve analysis. The mPCR-HRM was able to differentiate between C. jejuni and C. coli species. All DNA amplicons generated by mPCR were sequenced. Analysis of the nucleotide sequences from each isolate revealed that the HRM curves were correlated with the nucleotide sequences of the amplicons. Minor variation in melting point temperatures of C. coli or C. jejuni isolates was also observed and enabled some intraspecies differentiation between C. coli and/or C. jejuni isolates. The potential of PCR-HRM curve analysis for the detection and speciation of Campylobacter in additional human clinical specimens and chicken swab samples was also confirmed. The sensitivity and specificity of the test were found to be 100% and 92%, respectively. The results indicated that mPCR followed by HRM curve analysis provides a rapid (8 hours) technique for differentiation between C. jejuni and C. coli isolates.

Partial Failure of Milk Pasteurization as a Risk for the Transmission of Campylobacter From Cattle to Humans

BACKGROUND

Cattle are the second most common source of human campylobacteriosis. However, routes to account for this scale of transmission have not been identified. In contrast to chicken, red meat is not heavily contaminated at point of sale. Although effective pasteurization prevents milk-borne infection, apparently sporadic infections may include undetected outbreaks from raw or perhaps incompletely pasteurized milk.

METHODS

A rise in Campylobacter gastroenteritis in an isolated population was investigated using whole-genome sequencing (WGS), an epidemiological study, and environmental investigations.

RESULTS

A single strain was identified in 20 cases, clearly distinguishable from other local strains and a reference population by WGS. A case-case analysis showed association of infection with the outbreak strain and milk from a single dairy (odds ratio, 8; Fisher exact test P value = .023). Despite temperature records indicating effective pasteurization, mechanical faults likely to lead to incomplete pasteurization of part of the milk were identified by further testing and examination of internal components of dairy equipment.

CONCLUSIONS

Here, milk distribution concentrated on a small area, including school-aged children with low background incidence of campylobacteriosis, facilitated outbreak identification. Low-level contamination of widely distributed milk would not produce as detectable an outbreak signal. Such hidden outbreaks may contribute to the substantial burden of apparently sporadic Campylobacter from cattle where transmission routes are not certain. The effective discrimination of outbreak isolates from a reference population using WGS shows that integrating these data and approaches into surveillance could support the detection as well as investigation of such outbreaks.

Application of pulsed field gel electrophoresis to type Campylobacter jejuni

Pulsed field gel electrophoresis (PFGE) is generally accepted as one of the most discriminatory methods available for genotyping Campylobacter jejuni. PFGE has been extensively used in epidemiological studies, including outbreak investigation, persistence of genotypes in a human population, environmental diversity of sporadic infection isolates, dissemination of antibiotic-resistant strains, and comparison of genotypes within and between hosts. The main purpose of this chapter is to present a working PFGE protocol for those interested in incorporating this technique in their laboratories.

Raw milk consumption among patients with non-outbreak-related enteric infections, Minnesota, USA, 2001-2010

Raw milk has frequently been identified as the source of foodborne illness outbreaks; however, the number of illnesses ascertained as part of documented outbreaks likely represents a small proportion of the actual number of illnesses associated with this food product. Analysis of routine surveillance data involving illnesses caused by enteric pathogens that were reportable in Minnesota during 2001-2010 revealed that 3.7% of patients with sporadic, domestically acquired enteric infections had reported raw milk consumption during their exposure period. Children were disproportionately affected, and 76% of those <5 years of age were served raw milk from their own or a relative's farm. Severe illness was noted, including hemolytic uremic syndrome among 21% of Escherichia coli O157-infected patients reporting raw milk consumption, and 1 death was reported. Raw milk consumers, potential consumers, and policy makers who might consider relaxing regulations regarding raw milk sales should be educated regarding illnesses associated with raw milk consumption.

Current methods for molecular typing of Campylobacter species

Campylobacter remains one of the most common bacterial causes of gastroenteritis worldwide. Tracking sources of this organism is challenging due to the large numbers of human cases, and the prevalence of this organism throughout the environment due to growth in a wide range of animal species. Many molecular subtyping methods have been developed to characterize Campylobacter species, but only a few are commonly used in molecular epidemiology studies. This review examines the applicability of these methods, as well as the role that emerging whole genome sequencing technologies will play in tracking sources of Campylobacter spp. infection.

Comparison of molecular typing methods useful for detecting clusters of Campylobacter jejuni and C. coli isolates through routine surveillance

Campylobacter spp. may be responsible for unreported outbreaks of food-borne disease. The detection of these outbreaks is made more difficult by the fact that appropriate methods for detecting clusters of Campylobacter have not been well defined. We have compared the characteristics of five molecular typing methods on Campylobacter jejuni and C. coli isolates obtained from human and nonhuman sources during sentinel site surveillance during a 3-year period. Comparative genomic fingerprinting (CGF) appears to be one of the optimal methods for the detection of clusters of cases, and it could be supplemented by the sequencing of the flaA gene short variable region (flaA SVR sequence typing), with or without subsequent multilocus sequence typing (MLST). Different methods may be optimal for uncovering different aspects of source attribution. Finally, the use of several different molecular typing or analysis methods for comparing individuals within a population reveals much more about that population than a single method. Similarly, comparing several different typing methods reveals a great deal about differences in how the methods group individuals within the population.

Outbreaks of campylobacteriosis in Australia, 2001 to 2006

The objective of this study was to examine the frequency of Campylobacter outbreaks in Australia and determine common transmission routes and vehicles. Summary and unit data on Campylobacter outbreaks that occurred between January 2001 and December 2006 were systematically collected and analyzed. Data from Campylobacter mandatory notifications for the same period were used for comparison. During the study period there were 33 Campylobacter outbreaks reported, affecting 457 persons. Of these, 147 (32%) had laboratory-confirmed infections, constituting 0.1% of notified Campylobacter cases. Campylobacter outbreaks most commonly occurred during the Australian Spring (September to November; n = 14, 45%), when notifications generally peaked. Transmission was predominantly foodborne or suspected foodborne (n = 27, 82%), commercial settings (n = 15, 55%) being most commonly involved. There were eight foodborne outbreaks (30%) attributed to food prepared or eaten at institutions; four (15%) at aged care facilities and three (11%) at school camps. A vehicle or suspected vehicle was determined for 16 (59%) foodborne outbreaks; poultry (chicken or duck) was associated with 11 (41%) of these, unpasteurized milk and salad were associated with two outbreaks each. Three potential waterborne outbreaks were detected, and one was due to person-to-person transmission. Campylobacter outbreaks were more commonly detected during this study period compared to a previous 6-year period (n = 9) when prospective recording of information was not undertaken. However, outbreak cases continue to constitute a very small proportion of notifications. Improved recognition through subtyping is required to enhance outbreak detection and investigation so as to aid policy formulation for prevention of infection. In addition to detection of chicken as a common source of outbreaks, these data highlight the importance of directing policy at commercial premises, aged care facilities, and school camps to reduce Campylobacter disease burden.

Genetic and Epidemiological Relationships among Campylobacter Isolates from Humans

84 Campylobacter jejuni isolates from Swedish patients with domestic infection were characterized with pulsed-field gel electrophoresis (PFGE), and the subtype information considered in relation to epidemiological data. Based on pattern combinations from restriction cleavage with SmaI and SalI, 52 different PFGE types were identified. Types with an average pattern similarity of at least 82% and 63% were assembled in groups and clusters, respectively. The 2 largest clusters included 71% of the isolates. The distribution in time varied between different groups and clusters, where some were isolated sporadically during the whole period and others appeared more concentrated in time. Types in 1 cluster were significantly more often isolated in summer than other types in the study. Isolates from children showed lower pattern similarity to other isolates than isolates from adults. Sets of type and time related cases, possibly representing small outbreaks, were identified when indistinguishable PFGE patterns were found in isolates from temporally related cases. Our results indicate that although a large number of genotypes may be found among C. jejuni strains infecting humans, a large proportion of these may be genetically related, and that different genotypes may appear during different seasons and infect individuals of different ages.

Impact of compounding error on strategies for subtyping pathogenic bacteria

Comparative-omics will identify a multitude of markers that can be used for intraspecific discrimination between strains of bacteria. It seems intuitive that with this plethora of markers we can construct higher resolution subtyping assays using discrete markers to define strain "barcodes." Unfortunately, with each new marker added to an assay, overall assay robustness declines because errors are compounded exponentially. For example, the difference in accuracy of strain classification for an assay with 60 markers will change from 99.9% to 54.7% when average probe accuracy declines from 99.999% to 99.0%. To illustrate this effect empirically, we constructed a 19 probe bead-array for subtyping Listeria monocytogenes and showed that despite seemingly reliable individual probe accuracy (>97%), our best classification results at the strain level were <75%. A more robust strategy would use as few markers as possible to achieve strain discrimination. Consequently, we developed two variable number of tandem repeat (VNTR) assays (Vibrio parahaemolyticus and L. monocytogenes) and demonstrate that these assays along with a published assay (Salmonella enterica) produce robust results when products were machine scored. The discriminatory ability with four to seven VNTR loci was comparable to pulsed-field gel electrophoresis. Passage experiments showed some instability with ca. 5% of passaged lines showing evidence for new alleles within 30 days (V. parahaemolyticus and S. enterica). Changes were limited to a single locus and allele so conservative rules can be used to determine strain matching. Most importantly, VNTRs appear robust and portable and can clearly discriminate between strains with relatively few loci thereby limiting effects of compounding error.

Multilocus sequence typing of Campylobacter jejuni isolates from humans, chickens, raw milk, and environmental water in Quebec, Canada

Molecular strain typing is essential for deciphering the epidemiology of Campylobacter jejuni infections. We applied two different methods, multilocus sequence typing (MLST) and analysis of the flaA short variable repeat (SVR), to 289 isolates (163 human, 56 chicken, 34 raw milk, and 36 environmental water isolates) collected in the province of Québec, Canada, over 3 years; in addition, the analysis included the pulsed-field gel electrophoresis (PFGE) typing results for a subset of 131 isolates studied previously. MLST defined 96 sequence types (STs) and 20 clonal complexes (CCs), including 49 STs (73 isolates, 25%) and 39 alleles not previously documented in an international database. The frequency of new STs was significantly higher among water isolates than among isolates from other sources (18/36 [50%] and 55/253 [22%], respectively; P < 0.001). Nine of the 10 most prevalent CCs included isolates from humans and at least one other source; five CCs comprised exclusively or mostly human and chicken isolates. However, water and milk were the predominant nonhuman sources among the remaining CCs, suggesting that sporadic C. jejuni infections in humans may frequently arise from sources other than chickens. All three typing systems were discriminatory (discriminatory index > 0.9). Among 131 isolates analyzed by PFGE, each of the 20 types represented by two or more isolates corresponded to a single CC. In contrast, among the 14 most prevalent types detected by analysis of the flaA SVR (5 to 27 isolates each), 8 (57%) included isolates that represented multiple different CCs. The basis for these discordant results was uncertain. Antimicrobial resistance was randomly distributed among the CCs and appeared to be more closely related to the source of an isolate than its genotype. Although MLST is labor-intensive and expensive, it remains the single best method for the genotyping of C. jejuni isolates and deciphering the epidemiologic relationships among isolates.

Risk factors for infection with Campylobacter jejuni flaA genotypes

We aimed to explore Campylobacter genotype-specific risk factors in Australia. Isolates collected prospectively from cases recruited into a case-control study were genotyped using flaA restriction fragment-length polymorphism typing (flaA genotyping). Exposure information for cases and controls was collected by telephone interview. Risk factors were examined for major flaA genotypes using logistic and multinomial regression. Five flaA genotypes accounted for 325 of 590 (55%) cases - flaA-6b (n=129), flaA-6 (n=70), flaA-10 (n=48), flaA-2 (n=43), flaA-131 (n=35). In Australia, infections due to flaA-10 and flaA-2 were found to be significantly associated with eating non-poultry meat (beef and ham, respectively) in both case-control and inter-genotype comparisons. All major genotypes apart from flaA-10 were associated with chicken consumption in the case-control comparisons. Based on several clinical criteria, infections due to flaA-2 were more severe than those due to other genotypes. Thus genotype analysis may reveal genotype-specific niches and differences in virulence and transmission routes.

Clonal complexes of Campylobacter jejuni identified by multilocus sequence typing are reliably predicted by restriction fragment length polymorphism analyses of the flaA gene

Multilocus sequence typing (MLST) has provided important new insights into the population structure of Campylobacter jejuni and is rapidly becoming the gold standard for typing this species. However, the methodology is comparatively costly and slow to perform for the routine surveillance testing of large numbers of isolates required by public health laboratories. Restriction fragment length polymorphism analysis of the flaA gene (RFLP-flaA) and sequencing of the variable region in the fla locus (SVR-fla) were compared to MLST to determine if a low cost alternative could be found that reliably predicts clonal lineage (as determined by MLST). An isolate of C. jejuni from each of 153 patients from New South Wales, Australia, collected sequentially over a period of 30 months from 1999 to 2001 and comprising 40 sequence types (ST) from 15 clonal complexes (CC) was examined. Of 15 CC, 12 were represented by more than one isolate and a predominant RFLP-flaA type was found for 10 (83%). Of these, seven (70%) correctly predicted the predominant MLST CC with a probability of >0.8. Of 40 STs detected, 19 were reported for the first time, 9 of which were represented by more than one isolate. Eight of these were represented by a single RFLP-flaA type. Only two of eight major SVR-fla types were able to predict CC with a probability of >0.8, indicating that flaA-RFLP is a more reliable predictor of CC than SVR-fla and thus offers an alternative to MLST for use in routine surveillance.

Application of pulsed-field gel electrophoresis to identify potential outbreaks of campylobacteriosis in New Zealand

Since 2002, New Zealand's incidence of campylobacteriosis has exceeded 300 cases per 100,000 people per annum. To evaluate genetic variation in human isolates, 183 Campylobacter isolates were collected from a single clinical laboratory in Christchurch: 77 during an 8-week period in spring, and the rest 3 months later over a second 8-week period in autumn. Isolates were identified to the species level and subtyped using Penner serotyping (Campylobacter jejuni only) and pulsed-field gel electrophoresis (PFGE) using both SmaI and KpnI. Approximately two-thirds of the isolates could be grouped into clusters of between 2 and 26 isolates with indistinguishable SmaI and KpnI patterns. Less than 10% of the isolates were of the same type between the two sampling periods. The epidemiological relevance of the PFGE clusters was supported by temporal clustering, some spatial clustering, and some statistically significant demographic similarities among cases in a cluster. Conversely, patient cases yielding isolates which did not cluster with isolates from other cases were more likely to report recent overseas travel and less likely to live within larger urban centers. To identify whether these clusters actually represent common-source outbreaks, however, would require the detailed, rapid, and reiterative epidemiological investigation of cases within a PFGE cluster. The combined and timely application of subtyping and epidemiological investigation would appear to be a promising strategy for understanding campylobacteriosis in New Zealand.

Use of the oxford multilocus sequence typing protocol and sequencing of the flagellin short variable region to characterize isolates from a large outbreak of waterborne Campylobacter sp. strains in Walkerton, Ontario, Canada

The Walkerton (Ontario, Canada) outbreak of waterborne Escherichia coli O157:H7 and Campylobacter jejuni was quite limited in both space and time, making it a good model for exploring the utility of different typing and subtyping methods for the characterization of relationships among isolates of these organisms. We have extended previous work with these organisms through analysis by the Oxford multilocus sequence typing (MLST) and the flagellin short variable region (fla-SVR) sequencing methods. Additional isolates not epidemiologically related to the Walkerton outbreak have also been included. Both sequencing methods identified and differentiated between Walkerton outbreak strains 1 and 2. When these strains were compared with isolates that were not part of the outbreak, the information produced by the fla-SVR method more often correlated with epidemiological findings than that produced by MLST, though both methods were required for optimal discrimination. The MLST data were more relevant in terms of the overall population structure of the organisms. Both mutation and recombination appeared to be responsible for generating diversity among the isolates tested.

Role of real-time molecular typing in the surveillance of Campylobacter enteritis and comparison of pulsed-field gel electrophoresis profiles from chicken and human isolates

The goal of the present study was to assess the contribution of real-time molecular typing, used alone or with clinical surveillance, to the prompt identification of clusters of Campylobacter enteritis. Potential poultry sources were sought by comparing the pulsed-field gel electrophoresis genotypes of human and fresh whole retail chicken isolates collected during the same study period. Among 183 human isolates, 82 (45%) had unique genotypes, 72 (39%) represented 26 clusters of 2 to 7 isolates each, and 29 (16%) represented three clusters of 8 to 11 isolates each. Molecular typing was useful for the confirmation of outbreaks suspected on the basis of epidemiological surveillance, but for most small clusters, no epidemiological link could be established. Thus, the added value of real-time molecular typing is questionable, since the numerous small clusters identified were of unclear public health significance. Among 177 chickens, 41 (23%) yielded campylobacter isolates; of these, 19 (46%) had genotypes similar to those of 41 (22%) human isolates. However, a temporal association was demonstrated in only a minority of cases, and most genotypes were present only in a single species, suggesting that sources other than chickens are important in human campylobacteriosis. Further investigation with samples from water and other possible environmental sources is needed to define the most efficient strategy for the application of molecular typing and identification of the source(s) of sporadic cases of campylobacteriosis.