Figure 4.

Graphical and historical overview of food item categories (types) for human consumption tested for C. difficile: (1981–2019). Contextualization of food items tested across continental regions. For a historic narrative see Results section. ^*First studies relevant to risk of ingestion C. difficile and food microbial safety epidemiology. ^aFirst study in human hospital menus; negative results. Others (36, 44, 52) yielded positive results (112). ^bFirst isolation from food produced by invertebrate insects—honey. ^cFirst study in drinking water. ^dFirst isolation of C. difficile from retail raw root vegetables. ^eFirst isolation of C. difficile from animal-derived meat product, incidental finding while studying clostridia in spoiled and blown vacuumed packed sausages. No recognition of relevance to human health. ^fFirst study on retail food derived from farm animals destined for mass scale production of food for humans with genotyping evidence of C. difficile hyper-virulent strains present in retail foods. Isolates obtained from retail ground beef purchased in Guelph, Ontario, Canada, 2004–2005. PCR ribotypes had assigned international nomenclature by Dr. Jon Brazier, U. of Wales, UK. ^gFirst national systematic sampling study reporting seasonality of C. difficile in foods, Canada, 2006.