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. 2019 Sep 5;45(9):225-229.
doi: 10.14745/ccdr.v45i09a01.

Use of a case-control study and control bank to investigate an outbreak of locally acquired cyclosporiasis in Canada, 2016

V Morton  1 , K Meghnath  2 , M Gheorghe  2 , A Fitzgerald-Husek  3 , J Hobbs  4 , L Honish  5 , S David  6
Affiliations

Use of a case-control study and control bank to investigate an outbreak of locally acquired cyclosporiasis in Canada, 2016

V Morton et al. Can Commun Dis Rep. .

Abstract

Background: Cyclospora is an intestinal parasite that is not endemic in Canada. However, national outbreaks of locally acquired cases have been reported since 2013. These outbreaks were suspected to be associated with consumption of produce imported from countries where Cyclospora is endemic. Identification of the source can be challenging because of reporting delays and limited traceability of produce.

Objective: To report on a national outbreak of locally acquired cyclosporiasis, highlight the challenges of investigating these outbreaks and document the first time use of a control bank to recruit controls for a national outbreak case-control study in Canada.

Methods: Cases of cyclosporiasis were identified through provincial laboratory testing and reported through provinces to the national level. Cases were interviewed about food exposures using a questionnaire and food exposures reported by cases were compared to Foodbook reference values. To narrow down the food items of interest, a matched case-control study was conducted. Controls for the study were recruited primarily from a control bank, that is, a list of individuals who had previously agreed to participate in public health-related surveys.

Results: In total, 87 cases of locally acquired cyclosporiasis with onset or report dates between May 19, 2016 and August 10, 2016 were reported by four provinces. Comparing case exposures to Foodbook reference values identified several food items of interest, including blackberries, other berries, herbs and leafy greens. The case-control study identified only blackberries and mesclun greens as significantly more frequently consumed by cases than controls. Due to lack of product details for blackberries and mesclun greens, the source of the outbreak was not conclusively identified.

Conclusion: Blackberries were the primary food item of interest, but could not be identified as the conclusive source due to lack of traceability. The control bank was found to be a useful tool for control recruitment.

Keywords: Canada; Cyclospora; case–control study; cyclosporiasis; outbreak.

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Conflict of interest statement

Conflict of interest: None.

Figures

Figure 1
Figure 1
Number of confirmed outbreak cases of locally acquired cyclosporiasis by symptom onset or specimen collection date and status of inclusion/exclusion in the case–control study, 2016, Canadaa a One outbreak case was excluded as no symptom onset date or specimen collection date was available; only an isolation date was available
See this image and copyright information in PMC

References

    1. Heymann DL, editor. Control of communicable diseases manual. 20th edition. Washington (DC): American Public Health Association; 2014.
    1. Hedberg CW, Osterholm MT. Foodborne outbreaks caused by Cyclospora: the message is more important than the messenger [PubMed]. Epidemiol Infect 2016. Jul;144(9):1803–6. 10.1017/S0950268815002356 - DOI - PMC - PubMed
    1. Herwaldt BL, Beach MJ; Cyclospora Working Group. The return of Cyclospora in 1997: another outbreak of cyclosporiasis in North America associated with imported raspberries [PubMed]. Ann Intern Med 1999. Feb;130(3):210–20. 10.7326/0003-4819-130-3-199902020-00006 - DOI - PubMed
    1. CIFOR. Guidelines for foodborne disease outbreak response (CIFOR Guidelines). Atlanta (GA): Council to Improve Foodborne Outbreak Response; 2009. https://cifor.us/products/guidelines
    1. Munnoch SA, Ward K, Sheridan S, Fitzsimmons GJ, Shadbolt CT, Piispanen JP, Wang Q, Ward TJ, Worgan TL, Oxenford C, Musto JA, McAnulty J, Durrheim DN. A multi-state outbreak of Salmonella Saintpaul in Australia associated with cantaloupe consumption [PubMed]. Epidemiol Infect 2009 Mar;137(3):367–74. 10.1017/S0950268808000861 - PubMed