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Public Health Agency of Canada (PHAC)
Canada Communicable Disease Report

Volume 26-19
1 October 2000

[Table of Contents]

  

CASE-CONTROL STUDY ASSESSING THE ASSOCIATION BETWEEN YERSINIOSIS AND EXPOSURE TO SALAMI

Introduction

In November 1999, an outbreak of Escherichia coli O157:H7 gastroenteritis was identified by the British Columbia Centre for Disease Control Society (BCCDCS). An outbreak investigation by local, provincial, and federal health officials identified the source of the outbreak as salami, a dry, fermented meat product consisting of approximately 80% pork and 20% beef (1). The implicated product was recalled from the market.

During the same period (25 October to 30 November 1999), a number of yersiniosis cases in British Columbia (B.C.) also reported exposure to fermented meat products. As a result, a retrospective case-control study was initiated to determine if there was an association between yersiniosis and consumption of dry, fermented meat products.

Methods

Cases enrolled in the study were residents of four regional health authorities. Yersinia species had been isolated from the case-patients' stool by outpatient or hospital laboratories and reported to public-health authorities between 25 October and 30 November 1999. Cases who reported travel 2 weeks prior to their onset of symptoms were excluded from the study.

For each identified case, one age-, sex- and geographically-matched control was recruited. Potential controls were voluntarily nominated by the case-patients. In instances where the case-patients were not able to nominate a control, the B.C. population-based client registry was used to generate controls. Three age- and sex-matched persons who lived in the case-patient's health region were identified from the registry and sequentially telephoned until one agreed to act as a control. Exclusion criteria for controls were any diarrheal or abdominal pain episodes in the preceding month.

Environmental health officers, public-health nurses, and epidemiologists conducted telephone interviews with the cases and controls, using a standardized questionnaire. Cases were queried about the 2-week period before the onset of symptoms. In instances where onset of illness could not be recalled, cases were asked about the 2 weeks prior to specimen submission to the laboratory. Controls were asked about the same 2-week period as their matched case-patient. Enrollees were asked about travel activities and foods consumed, specifically salami, during the period of interest.

The salami products that were submitted to the provincial laboratory during the E. coli O157:H7 outbreak investigation were further tested using direct and cold enrichment methods of examination for the presence of Y. enterocolitica. Analytical procedures were based on the United States Food and Drug Administration Bacteriological Analytical Manual(2).

Results

Forty-seven persons with yersiniosis were identified in the four regional health authorities during the study period. Of the 47 cases, 19 (40.4%) of the eligible cases were enrolled in the case-control study. The remaining 28 cases were either not available, refused interview, or could not be matched with a suitable control. For each case-patient, one age-, sex- and geographically-matched control was enrolled. The mean age of the case-patients was 33 years old (range: 1 to 74 years). Of the case-patients, 68% were females and 32% were males.

On univariate analysis, salami consumption was associated with illness (Mantel-Haenszel matched odds ratio of 9.00, 95% confidence interval: 1.25 to 395, p = 0.027). Forty-seven percent of the case-patients and 5% of controls reported consuming salami prior to the onset of symptoms or specimen submission to the laboratory.

Of the 45 salami products submitted for the E. coli O157:H7 outbreak investigation, only six had sufficient amounts for further testing. Y. enterocolitica was not isolated in any of the six salami products.

Discussion

This study found an epidemiologic association between cases of yersiniosis and consumption of salami products. This finding compliments the findings of a Norwegian study documenting an association between yersiniosis cases and consumption of various sausage products(3). In addition, this study strengthens the evidence of other epidemiological studies that have repeatedly linked Yersinia species to a porcine reservoir and have associated cases of yersiniosis to the consumption of undercooked pork products(4,5).

Although the association between the sporadic cases of yersiniosis and exposure to salami is significant, we must be cautious when interpreting the results. Overall, 47% of the case-patients reported exposure to salami compared to 5% of the controls. This difference may be due to differences in recall to questions between case-patients and controls. In addition, case-patients may have had knowledge of the E. coli outbreak and its linkage to various salami products. To validate our findings, future studies in high incidence areas are needed.

The majority of cases infected with Yersinia suffer various symptoms of gastroenteritis. More serious cases can lead to polyarthritis, septicemia, and meningitis(6). These consequences along with the high incidence rates (28 per 100,000 population for 1998) in B.C. make yersiniosis a significant public-health problem. Based on the findings of this study, recommendations include:

  • Review the parameters set for the intrinsic factors (pH and water activity) of all dry, fermented meat products to ensure environment inhibits the growth of Yersinia.
  • Initiate research to identify risk factors associated with Yersinia infections.

Acknowledgment

The efforts and contribution of numerous individuals at the regional health levels are greatly appreciated and acknowledged.

References

  1. Fyfe M. Outbreak of E. coli O157:H7 infection associated with salami. Presented at Canadian Institute of Public Health Inspector Conference, 9-12 April 2000, Vancouver, B.C.

  2. United States Food and Drug Administration. Bacteriological Analytical Manual. 8th ed. Gaithersburg, MD: AOAC International 1995:8.01-8.13.

  3. Ostroff SM, Kapperud G, Hutwagner LC et al. Sources of sporadic Yersinia enterocolitica infections in Norway: a prospective case-control study. Epidemiol Infect 1994;112:133-41.

  4. Tauxe RV, Vandepitte J, Wauters G et al. Yersinia enterocolitica infections and pork: the missing link. Lancet 1987;1:1129-132.

  5. Satterthwaite P, Pritchard K, Floyd D. Case-control study of yersinia infections in Auckland. Australian and New Zealand Journal of Public Health 1999;23:482-85.

  6. Benenson AS, ed. Yersiniosis. In: Control of communicable disease manual. 16th ed. Washington, DC: American Public Health Association 1995:558-61.

Source: J Harb, MSc, BA, CPHI(C), BCCDCS Field Epidemiologist, Field Epidemiology Training Program, Centre for Surveillance Coordination, Health Canada, Vancouver, B.C.; M Fyfe, MD, MHSc, Associate Director, D Patrick, MD, MHSc, Director, Communicable Disease Epidemiology Services, A Trinidad, BSc, B.C. Provincial Laboratory, BCCDCS, Vancouver, B.C.; J Hockin, MD, MSc, Director, Field Epidemiology Training Program, Health Canada, Ottawa, Ont.; N Masoud, CPHI(C), North Shore Health Region, K Louie, CPHI(C), South Fraser Health Authority, C Kurzac, CPHI(C), Vancouver Richmond Health Authority, Vancouver, B.C.

 

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