Survey on changes in colorectal cancer screening participation at Minamisoma city after the Great East Japan earthquake using clustering analysis.

Objectives: Participation in colorectal cancer (CRC) screening is important. However, detailed analyses of pre- and post-disaster screening participation is lacking. We classified a population in terms of CRC screening participation pattern before and after the Great East Japan Earthquake and identified factors that are important in classifying people into such groups. Study design: Retrospective observational study. Methods: We analyzed 21 578 people who were consistently registered in the basic resident register of Minamisoma between 2009 and 2018, using non-hierarchical clustering with the k-means method. After clustering analysis, we identified the factors that distinguish groups with different post-disaster participation changes by classes with high and low pre-disaster participation rates using LightGBM. Results: Transition in screening participation rate was divided into four classes. Classes 1 and 2 had high pre-disaster participation; Class 1 recovered after a decline, while Class 2 stayed low, mainly among those still evacuated. The factors separating the two groups were age, sex, and evacuation status. Class 3 and 4 had low pre-disaster rates; Class 3 increased participation post-disaster, especially among individuals under 53 years old. The factors separating the two groups were age and sex. Conclusions: Our analysis revealed that CRC screening participation declined among evacuees who had previously participated in screening but increased among older individuals who had not participated before the disaster. Post-disaster screening strategies should be tailored to these groups.