Longitudinal screening adherence in the Australian National Bowel Cancer Screening Program from 2006 to 2022

Objective: Australia's National Bowel Cancer Screening Program (NBCSP) offers two-yearly screening to 50-74year-olds for the prevention and early detection of colorectal cancer (CRC). Internationally, detailed reporting of participation across multiple screening rounds - also known as longitudinal adherence - is becoming more common, but remains limited in Australia. We described the longitudinal screening adherence of individuals by age and sex invited to the NBCSP at least once, and quantified longitudinal adherence among individuals who received four NBCSP invitations. Methods: We obtained aggregate national data for individuals who received at least one NBCSP invitation between 1 August 2006 and 31 March 2022. We described screening adherence patterns including longitudinal adherence among individuals who received four invitations, and evaluated prior longitudinal adherence and adherence at most recent invitation as predictors of future participation. Results: Over the study period, 8.5 million individuals were invited to screen in the NBCSP; 51.9% of these individuals screened at least once. Of the >2.5 million individuals who received four invitations, 23.3% consistently screened, 38.3% never screened, and 38.3% inconsistently screened. The longitudinal adherence at the fourth invitation round for individuals who previously returned none, one, two, or three of their previous three invitations was 9.5%, 37.4%, 70.1% and 88.8%, respectively. Both longitudinal adherence and adherence at the most recent invitation were significant predictors of future participation. Conclusion: Our study is the first detailed report of longitudinal adherence to the NBCSP in >2 screening rounds. These insights into long-term behaviours can inform planning for interventions to improve screening participation.