Nationwide participation in FIT-based colorectal cancer screening in Denmark during the COVID-19 pandemic: An observational study.

Background: Worldwide, most colorectal cancer screening programmes were paused at the start of the COVID-19 pandemic, while the Danish faecal immunochemical test (FIT)-based programme continued without pausing. We examined colorectal cancer screening participation and compliance with subsequent colonoscopy in Denmark throughout the pandemic. Methods: We used data from the Danish Colorectal Cancer Screening Database among individuals aged 50-74 years old invited to participate in colorectal cancer screening from 2018 to 2021 combined with population-wide registries. Using a generalised linear model, we estimated prevalence ratios (PRs) and 95% confidence intervals (CIs) of colorectal cancer screening participation within 90 days since invitation and compliance with colonoscopy within 60 days since a positive FIT test during the pandemic in comparison with the previous years adjusting for age, month and year of invitation. Results: Altogether, 3,133,947 invitations were sent out to 1,928,725 individuals and there were 94,373 positive FIT tests (in 92,848 individuals) during the study period. Before the pandemic, 60.7% participated in screening within 90 days. A minor reduction in participation was observed at the start of the pandemic (PR = 0.95; 95% CI: 0.94-0.96 in pre-lockdown and PR = 0.85; 95% CI: 0.85-0.86 in first lockdown) corresponding to a participation rate of 54.9% during pre-lockdown and 53.0% during first lockdown. This was followed by a 5-10% increased participation in screening corresponding to a participation rate of up to 64.9%. The largest increase in participation was observed among 55-59 years old and among immigrants. The compliance with colonoscopy within 60 days was 89.9% before the pandemic. A slight reduction was observed during first lockdown (PR = 0.96; 95% CI: 0.93-0.98), where after it resumed to normal levels. Conclusions: Participation in the Danish FIT-based colorectal cancer screening programme and subsequent compliance to colonoscopy after a positive FIT result was only slightly affected by the COVID-19 pandemic. Funding: The study was funded by the Danish Cancer Society Scientific Committee (Grant number R321-A17417) and the Danish regions.