The impact of COVID-19 on participation in Australia's National Bowel Cancer Screening Program by people with severe mental illness: A national data linkage study.

Objective: The impact of COVID-19 on Australia's National Bowel Cancer Screening Program remains unclear, especially for individuals with severe mental illness. These individuals have historically participated in the National Bowel Cancer Screening Program at significantly lower rates than the general population. This study aimed to understand the impact of COVID-19 on participation in Australia's National Bowel Cancer Screening Program among individuals with severe mental illness.

Methods: Cohort study using deidentified linked health and National Bowel Cancer Screening Program data. We compared participation in the National Bowel Cancer Screening Program between individuals with and without severe mental illness by examining rates of participation (returning an immunochemical faecal occult blood test), returning a valid immunochemical faecal occult blood test, receiving a positive immunochemical faecal occult blood test result and undergoing a follow-up colonoscopy before (25 January 2018-24 January 2020) and during (25 January 2020-31 July 2021) the COVID-19 pandemic.

Results: Overall National Bowel Cancer Screening Program participation fell by 10.3% from pre-COVID to during COVID. Less than one-quarter (23.9%) of people with severe mental illness participated in the National Bowel Cancer Screening Program during the COVID-19 pandemic compared to 30.5% before. People with severe mental illness were less likely to return a valid immunochemical faecal occult blood test and more likely to return a positive immunochemical faecal occult blood test result both before and during the pandemic, compared to the general population. They were also significantly less likely to have a colonoscopy following positive immunochemical faecal occult blood test result (pre-COVID adjusted relative risk = 0.97, 95% confidence interval: 0.94-1.01, vs during COVID adjusted relative risk = 0.87, 95% CI: 0.82-0.91).

Conclusion: The pandemic significantly reduced the rate at which all Australians participated in the National Bowel Cancer Screening Program. Disparities between people with severe mental illness and the general population generally improved with the exception of follow-up colonoscopy after positive immunochemical faecal occult blood test result.