Outbreaks of Yersinia pseudotuberculosis infection have been epidemiologically linked to fresh produce, but the bacterium has not been recovered from the food items implicated. In May 2003, a cluster of gastrointestinal illness and erythema nodosum was detected among schoolchildren who had eaten lunches prepared by the same institutional kitchen.
We conducted a case-control study and trace-back, environmental, and laboratory investigations. Case patients had culture-confirmed Y. pseudotuberculosis O:1 infection, erythema nodosum, or reactive arthritis. Bacterial isolates from clinical and environmental samples were compared using pulsed-field gel electrophoresis (PFGE).
Of 7392 persons at risk, 111 (1.5%) met the case definition; 76 case patients and 172 healthy control subjects were enrolled in the case-control study. Only raw grated carrots were significantly associated with illness in a logistic-regression model (multivariable odds ratio, 5.7 [95% confidence interval, 1.7-19.5]); a dose response was found for increasing amount of consumption. Y. pseudotuberculosis O:1 isolates from 39 stool specimens and from 5 (42%) of 12 soil samples that contained carrot residue and were obtained from peeling and washing equipment at the production farm were indistinguishable by PFGE.
Carrots contaminated early in the production process caused a large point-source outbreak. Our findings enable the development of evidence-based strategies to prevent outbreaks of this emerging foodborne pathogen.
Comment In: J Infect Dis. 2006 Nov 1;194(9):1191-317041842
Salmonella enterica, Campylobacter and Yersinia species, Shiga toxin-producing Escherichia coli (STEC), Listeria monocytogenes and Clostridium perfringens are the bacterial pathogens constituting the greatest burden of food-borne disease in Finland. Several molecular genetic methods have been applied to diagnose, discriminate and survey these bacteria. PCR, PCR-RFLP and PFGE are the most widely and successfully used. However, these methods are unable to replace conventional and internationally standardised phenotyping. Electronic database libraries of the different genomic profiles will enable continuous surveillance of infections and detection of possible infection clusters at an early stage. Furthermore, whole-genome sequence data have opened up new insights into epidemiological surveillance. Laboratory-based surveillance performed in a timely manner and exploiting adequate methods, and co-operation at local, national and international levels are among the key elements in preventing food-borne diseases. This paper reviews different applications of molecular genetic methods for investigating enteric bacterial pathogens and gives examples of the methods successfully used in diagnostics and epidemiological studies in Finland.
A substantial sampling among domestic human campylobacter cases, chicken process lots, and cattle at slaughter was performed during the seasonal peak of human infections. Campylobacter jejuni isolates (n = 419) were subtyped using pulsed-field gel electrophoresis with SmaI, and isolates representing overlapping types (n = 212) were further subtyped using KpnI for restriction. The SmaI/KpnI profiles of 55.4% (97/175) of the human isolates were indistinguishable from those of the chicken or cattle isolates. The overlapping SmaI/KpnI subtypes accounted for 69.8% (30/43) and 15.9% (32/201) of the chicken and cattle isolates, respectively. The occurrence of identical SmaI/KpnI subtypes with human C. jejuni isolates was significantly associated with animal host species (P
After heavy rains Campylobacter jejuni together with high counts of Escherichia coli, other coliforms and intestinal enterococci were detected from drinking water of a municipal distribution system in eastern Finland in August 2004. Three patients with a positive C. jejuni finding, who had drunk the contaminated water, were identified and interviewed. The pulsed-field gel electrophoresis (PFGE) genotypes from the patient samples were identical to some of the genotypes isolated from the water of the suspected contamination source. In addition, repetitive DNA element analysis (rep-PCR) revealed identical patterns of E. coli and other coliform isolates along the distribution line. Further on-site technical investigations revealed that one of the two rainwater gutters on the roof of the water storage tower had been in an incorrect position and rainwater had flushed a large amount of faecal material from wild birds into the drinking water. The findings required close co-operation between civil authorities, and application of cultivation and genotyping techniques strongly suggested that the municipal drinking water was the source of the infections. The faecal contamination associated with failures in cleaning and technical management stress the importance of instructions for waterworks personnel to perform maintenance work properly.
The genetic diversity of Campylobacter jejuni strains isolated from Finnish patients was studied by typing 508 strains by pulsed-field gel electrophoresis: 311 were isolated from domestically acquired infections and 197 from travel-related infections. The strains were systematically selected from a larger collection of previously serotyped strains isolated during two 1-year sampling periods. The four most common SmaI profiles accounted for 45% of the domestic strains but only 3% of the travel-related strains. Of the domestic strains, 69% belonged to SmaI subtypes found during both sampling periods. The predominating SmaI subtypes and strains that were not digested by SmaI were typed by KpnI. Analyzing the temporal diversity of the pulsed-field gel electrophoresis profiles revealed six common persistent SmaI/KpnI subtypes among the domestic strains. Five of them have been identified in cattle, and two in chickens with a temporal association with human infections.
The agar dilution method has been standardized by the CLSI for the susceptibility testing of Campylobacter species, and according to these standards, the disk diffusion method should be used only in screening for macrolide and ciprofloxacin resistance. Nevertheless, the disk diffusion test is currently widely used, since it is easy to perform in clinical microbiology laboratories. In this study, the disk diffusion method was compared to the agar dilution method by analyzing the in vitro activities of seven antimicrobial agents against 174 Campylobacter strains collected in Finland between 2003 and 2008. Recommendations of the CLSI were followed using Mueller-Hinton agar plates with 5% of sheep blood. For each strain, the disk diffusion tests were performed two to four times. Of the 33 erythromycin-resistant strains (MIC, =16 µg/ml), 24 (73%) constantly showed a 6-mm erythromycin inhibition zone (i.e., no inhibition), while for seven strains the inhibition zone varied from 6 to 44 mm in repeated measurements. Among the 141 erythromycin-susceptible strains (MIC,
Listeria monocytogenes strains that were isolated from 314 human listeriosis cases in Finland during an 11-year period were analyzed by O:H serotyping and pulsed-field gel electrophoresis (PFGE). Serotyping divided the isolates into five serotypes, the most common being 1/2a (53%) and 4b (27%). During the study period, the number of cases caused by serotype 1/2a increased from 22% in 1990 to 67% in 2001, and those caused by serotype 4b decreased from 61 to 27%, respectively. PFGE with restriction enzyme AscI divided the strains into 81 PFGE genotypes; among strains of serotypes 1/2a and 4b, 49 and 18 PFGE types were seen, respectively. PFGE type 1 (serotype 1/2a) was the most prevalent single type (37 strains). Together with six other, closely related PFGE types, PFGE type 1 formed a group of 71 strains, representing 23% of all 314 strains. Strains of PFGE type 1 have also been isolated from cold smoked fish, suggesting a source of human infections caused by this type. Moreover, PFGE type 24 (serotype 1/2c) was significantly associated with gender: 5% of 180 male subjects but none of 132 female subjects (P = 0.012). An electronic database library was created from the PFGE profiles to make possible the prompt detection of new emerging profiles and the tracing of potential infection clusters in the future.
A total of 50 Finnish bathing water samples and 34 sewage effluent samples originating from 17 locations were studied in the summers of 2006 and 2007. Campylobacter were present in 58% and adenoviruses in 12% of all bathing water samples; 53% of all sewage effluent samples were positive for Campylobacter spp. and 59% for adenoviruses. C. jejuni was the most common Campylobacter species found and human adenovirus serotype 41 was the most common identified adenovirus type. Bathing water temperature displayed a significant negative relationship with the occurrence of Campylobacter. One location had identical pulsed-field gel electrophoresis patterns of C. coli isolates in the bathing water and in sewage effluent, suggesting that sewage effluent was the source of C. coli at this bathing site. The counts of faecal indicator bacteria were not able to predict the presence of Campylobacter spp. or adenoviruses in the bathing waters. Thus the observed common presence of these pathogens in Finnish sewage effluents and bathing waters may represent a public health risk. The low water temperature in Finland may enhance the prevalence of Campylobacter in bathing waters. More attention needs to be paid to minimizing the concentrations of intestinal pathogens in bathing waters.