Sentinel surveillance and epidemiology of Clostridioides difficile in Denmark, 2016 to 2019

Background: Since 2008, Danish national surveillance of Clostridioides difficile has focused on binary toxin -positive strains in order to monitor epidemic types such as PCR ribotype (RT) 027 and 078. Additional sur-veillance is needed to provide a more unbiased repre-sentation of all strains from the clinical reservoir.Aim: Setting up a new sentinel surveillance scheme for an improved understanding of type distribution relative to time, geography and epidemiology, here presenting data from 2016 to 2019. Methods: For 24 weeks in spring and autumn each year between 2016 and 2019, all 10 Danish Departments of Clinical Microbiology collected faecal samples containing toxigenic C. dif-ficile. Isolates were typed at the national reference laboratory at Statens Serum Institut. The typing method in 2016-17 used tandem-repeat-sequence typing, while the typing method in 2018-19 was whole genome sequencing.Results: During the study period, the sentinel surveillance scheme included ca 14-15% of all Danish cases of C. difficile infections. Binary toxin-negative strains accounted for 75% and 16 of the 20 most prevalent types. The most common sequence types (ST) were ST2/13 (RT014/020) (19.5%), ST1 (RT027) (10.8%), ST11 (RT078) (6.7%), ST8 (RT002) (6.6%) and ST6 (RT005/117) (5.1%). The data also highlighted geographical differences, mostly related to ST1 and temporal decline of ST1 (p = 0.0008) and the increase of ST103 (p = 0.002), ST17 (p = 0.004) and ST37 (p = 0.003), the latter three binary toxin-negative.Conclusion: Sentinel surveillance allowed nationwide monitoring of geographical differences and temporal changes in C. difficile infections in Denmark, including emerging types, regardless of binary toxin status.

Automated summary

This study established a new sentinel surveillance scheme to monitor C. difficile infections in Denmark. The results showed geographical differences and temporal changes in the distribution of different types of C. difficile infections.