This is the first prospective, Australian population-based IBD incidence study. The incidence rates are among the highest reported in the literature of IBD.

There is an interrelationship between disease activity, illness perceptions, coping strategies, and depression and anxiety. These aspects of psychological processing provide a framework and direction for the psychological support that patients with CD require.

A high rate of inflammatory disease, frequent immunomodulator use in CD, and a low rate of surgery in both CD and UC were identified. In CD, ileal involvement and complex disease behavior are associated with a more severe disease course, while in UC a high CRP predicted this outcome.

Irritable Bowel Syndrome (IBS) is a common condition affecting around 10-20% of the population and associated with poorer psychological well-being and quality of life. The aim of the current study was to explore the efficacy of the Common Sense Model (CSM) using Structural Equation Modelling (SEM) in an IBS cohort. One hundred and thirty-one IBS patients (29 males, 102 females, mean age 38 years) participating in the IBSclinic.org.au pre-intervention assessment were included. Measures included IBS severity (Irritable Bowel Syndrome Severity Scoring System), coping patterns (Carver Brief COPE), visceral sensitivity (Visceral Sensitivity Index), illness perceptions (Brief Illness Perceptions Questionnaire), psychological distress (Depression, Anxiety and Stress Scale), and quality of life (IBS Quality of Life scale; IBS-QoL). Using SEM, a final model with an excellent fit was identified (χ (8) = 11.91, p = .16, χ/N = 1.49, CFI > .98, TLI > .96, SRMR < .05). Consistent with the CSM, Illness perceptions were significantly and directly influenced by IBS severity (β = .90, p < .001). Illness perceptions in turn directly influenced maladaptive coping (β = .40, p < .001) and visceral sensitivity (β = .70, p < .001). Maladaptive coping and visceral sensitivity were significantly associated with psychological distress (β = .55, p < .001; β = .22, p < .01) and IBS-QoL (β = -.28, p < .001; β = -.62, p < .001). Based on these findings, we argue that to augment the adverse impact of IBS severity on IBS-QoL and psychological distress, psychological interventions will be best to target the mediating psychological processes including illness beliefs, visceral sensitivity and maladaptive coping.

The burden of IBD in our local region is high. Demographic similarities allow these results to be applied to the broader Australian community. We propose that the number of existing and new cases each year in Australia has been previously underestimated. These revised figures will be important when planning the provision of health resources for these patients in the future and when assessing need for research funding priorities.