Retrospective evaluation of an integrated molecular-epidemiological approach to cyclosporiasis outbreak investigations - United States, 2021

Abstract

Cyclosporiasis results from an infection of the small intestine by Cyclospora parasites after ingestion of contaminated food or water, often leading to gastrointestinal distress. Recent developments in temporally linking genetically related Cyclospora isolates demonstrated effectiveness in supporting epidemiological investigations. We used 'temporal-genetic clusters' (TGCs) to investigate reported cyclosporiasis cases in the United States during the 2021 peak-period (1 May - 31 August 2021). Our approach split 655 genotyped isolates into 55 genetic clusters and 31 TGCs. We linked two large multi-state epidemiological clusters (Epidemiologic Cluster 1 [n = 136 cases, 54 genotyped] and Epidemiologic Cluster 2 [n = 42 cases, 15 genotyped]) to consumption of lettuce varieties; however, product traceback did not identify a specific product for either cluster due to the lack of detailed product information. To evaluate the utility of TGCs, we performed a retrospective case study comparing investigation outcomes of outbreaks first detected using epidemiological methods with those of the same outbreaks had TGCs been used to first detect them. Our study results indicate that adjustments to routine epidemiological approaches could link additional cases to epidemiological clusters of cyclosporiasis. Overall, we show that CDC's integrated genotyping and epidemiological investigations provide valuable insights into cyclosporiasis outbreaks in the United States.

Keywords: Cyclospora; Food-borne infections; Molecular epidemiology.

Figure 1.

Tree representing genetic cluster memberships. Each colour on the inner ring represents a distinct genetic cluster. The specimens highlighted in purple in the outer ring are from 2021, and the specimens highlighted in white in the outer ring are reference specimens from 2018 to 2020. The locations of TGC 2021_003 (Genetic Cluster 18) and TGC 2021_005 (Genetic Cluster 11) are annotated by text boxes. Genetic cluster 18 contains TGC 2020_001 from 2020, which was linked to the bagged salad mix outbreak.