Objectives To investigate the effect of general practice (GP) and general practitioner (GPR) endorsement for faecal occult blood test (FOBT)-based screening on maintenance of participation in screening over four successive screening rounds. Setting South Australian residents aged !50 years. Methods Random selection of four groups (n ¼ 600 per group): one from the Commonwealth electoral roll (ER) and three from the combined patient lists of two collaborating GPs (GP1, GP2, GP3). Subjects were mailed offers to screen using a faecal immunochemical test over four successive rounds, spaced approximately 18 months apart. The GP1 and ER groups were invited to screen without any endorsement from a GPR or medical practice; GP2 invitees received an invitation indicating support for screening from their medical practice; and GP3 invitations were printed on practice letterhead and were signed by a GPR. Results Multivariate analyses indicated that initial participation as well as re-participation over four successive rounds was significantly enhanced in the GP2 (39%, 42%, 45% and 44%) and GP3 groups (42%, 47%, 48% and 49%) relative to the ER group (33%, 37%, 40% and 36%). The analyses also indicated that 60 -69 year olds were most likely to participate in all rounds (relative risk [RR] 1.49, 1.39, 1.43 and 1.25), and men were generally less likely to participate than women in all screening rounds (RR 0.86, 0.84, 0.80 and 0.83). Conclusions Associating a GPR or medical practice of recent contact with an invitation to screen achieves better participation and re-participation than does an invitation from a centralized screening unit. Furthermore, enhanced participation can be achieved by practice endorsement alone without requiring actual GPR involvement.

Background: There is little information on longitudinal patterns of participation in faecal occult blood test (FOBT) based colorectal cancer (CRC) screening or on demographic or behavioural factors associated with participation in re-screening. The lack of an agreed system for describing participatory behaviour over multiple rounds also hampers our ability to report, understand and make use of observed associations. Our aims were to develop a system for describing patterns of participatory behaviour in FOBT-based CRC screening programs and to identify factors associated with particular behavioural patterns. Methods: A descriptive framework was developed and applied to a data extract of screening invitation outcomes over two rounds of the NBCSP. The proportion of invitees in each behaviour category was determined and associations between behaviour patterns and demographic and program factors were identified using multivariate analyses. Results: We considered ReParticipants, Dropouts, Late Entrants and Never Participants to be the most appropriate labels for the four possible observed participatory categories after two invitation rounds. The screening participation rate of the South Australian cohort of the NBCSP remained stable over two rounds at 51%, with second round Dropouts (10.3%) being balanced by Late Entrants (10.5%). Non-Participants comprised 38.7% of invitees. Relative to Re-Participants, Dropouts were older, more likely to be female, of lower SES, had changed their place of residence between offers had a positive test result in the first round. Late Entrants tended to be in the youngest age band. Conclusions: Specific demographic characteristics are associated with behavioural sub-groups defined by responses to 2 offers of CRC screening. Targeted group-specific strategies could reduce dropout behaviour or encourage those who declined the first invitation to participate in the second round. It will be important to keep first round participants engaged in order to maximise the benefit of a CRC screening program.