ABSTRACT
SUMMARY This study assesses the contribution of different sources of human campylobacteriosis in Denmark using two different source-attribution approaches. In total, 794 non-human isolates and 406 isolates from human cases (domestic, travel related, and cases with unknown travel history) were collected. Isolates were characterized by multilocus sequence typing, flaA typing and susceptibility to antibiotics. Both models used indicate that the major burden of human campylobacteriosis in Denmark originates from the domestic broiler chicken reservoir. The second most important reservoir was found to be cattle. The Asymmetric Island model attributed 52% [95% credibility interval (CrI) 37-67] to Danish chicken, 17% (95% CrI 3-33) to imported chicken, and 17% (95% CrI 7-28) to cattle. Similarly, the Campylobacter source-attribution model apportioned 38% (95% CrI 28-47) to Danish chicken, 14% (95% CrI 10-18) to imported chicken, and 16% (95% CrI 7-25) to cattle. The addition of flaA type as an extra discriminatory typing parameter did not change the attribution of cases markedly.
Subject(s)
Campylobacter Infections/epidemiology , Campylobacter Infections/veterinary , Campylobacter/isolation & purification , Foodborne Diseases/epidemiology , Animals , Anti-Bacterial Agents/pharmacology , Campylobacter/classification , Campylobacter/genetics , Cattle , Chickens , Denmark/epidemiology , Disease Reservoirs , Flagellin/genetics , Genotype , Humans , Microbial Sensitivity Tests , Multilocus Sequence TypingABSTRACT
Multiple-locus variable-number of tandem repeats analysis (MLVA) is widely used for typing of pathogens. Methods such as MLVA based on determining DNA fragment size by the use of capillary electrophoresis have an inherent problem as a considerable offset between measured and real (sequenced) lengths is commonly observed. This discrepancy arises from variation within the laboratory set-up used for fragment analysis. To obtain comparable results between laboratories using different set-ups, some form of calibration is a necessity. A simple approach is to use a set of calibration strains with known allele sizes and determine what compensation factors need to be applied under the chosen set-up conditions in order to obtain the correct allele sizes. We present here a proof-of-concept study showing that using such a set of calibration strains makes inter-laboratory comparison possible. In this study, 20 international laboratories analysed 15 test strains using a five-locus Salmonella enterica serovar Typhimurium MLVA scheme. When using compensation factors derived from a calibration set of 33 isolates, 99.4% (1,461/1,470) of the MLVA alleles of the test strains were assigned correctly, compared with 64.8% (952/1,470) without any compensation. After final analysis, 97.3% (286/294) of the test strains were assigned correct MLVA profiles. We therefore recommend this concept for obtaining comparable MLVA results.
Subject(s)
Clinical Laboratory Techniques/methods , Multilocus Sequence Typing/methods , Salmonella enterica/isolation & purification , Salmonella typhimurium/isolation & purification , Tandem Repeat Sequences/genetics , Alleles , Clinical Laboratory Techniques/instrumentation , Genotype , Humans , Multilocus Sequence Typing/instrumentation , Multilocus Sequence Typing/standards , Practice Guidelines as Topic , Salmonella enterica/classification , Salmonella enterica/genetics , Salmonella typhimurium/classification , Salmonella typhimurium/geneticsABSTRACT
An outbreak of listeriosis in Denmark occurred in May 2009. Multilocus variable number of tandem repeats analysis typing, later confirmed by pulsed-field gel electrophoresis typing, showed that isolates from eight patients had identical patterns and were distinguishable from Listeria monocytogenes isolates from other Danish patients. Seven out of eight patients had received a meal with beef from the same meals-on-wheels delivery catering company 3 weeks prior to onset of disease. Two patients died of their infection. Large-scale delivery of precooked meals to a vulnerable population represents a threat if proper measures against listeriosis are not taken.
Subject(s)
Disease Outbreaks , Food Microbiology , Food Services , Foodborne Diseases/epidemiology , Listeriosis/epidemiology , Meat/microbiology , Adult , Aged , Aged, 80 and over , Denmark , Electrophoresis, Gel, Pulsed-Field , Female , Foodborne Diseases/diagnosis , Foodborne Diseases/mortality , Humans , Listeria monocytogenes/physiology , Listeriosis/diagnosis , Listeriosis/mortality , Male , Middle AgedABSTRACT
Multilocus variable number of tandem repeats analysis (MLVA) has recently become a widely used highly discriminatory molecular method for typing of the foodborne pathogen Salmonella Typhimurium. This method is based on amplification and fragment size analysis of five repeat loci. To be able to easily compare MLVA results between laboratories there is a need for a simple and definitive nomenclature for MLVA profiles. Based on MLVA results for all human S. Typhimurium isolates in Denmark from the last five years and sequence analysis of a selection of these isolates, we propose a MLVA nomenclature that indicates the actual number of repeat units in each locus. This nomenclature is independent of the equipment used for fragment analysis and, in principle, independent of the primers used. A set of reference strains is developed that can be used for easy normalisation of fragment sizes in each laboratory.
