Background: Disease severity, illness perceptions, coping strategies, stress, psychological well-being, and quality of life were reported to have close relationships. According to the Common Sense Model, illness perceptions and coping strategies could mediate the relationship between illness stimuli and illness outcomes such as psychological health and quality of life. Stress was also associated with the individual's disease severity, anxiety, depression, and quality of life.

Objectives: The study aimed to explore the influencing factors of illness outcomes, and to what extent illness perceptions, coping strategies, and stress mediate the relationship between disease severity and anxiety, and depression and quality of life.

Methods: Our study included 159 patients with Crohn's disease who were attending a tertiary hospital outpatient clinic or who were hospitalized. Disease severity was measured with the Crohn's Disease Activity Index. Illness perceptions were measured with the Brief Illness Perceptions Questionnaire. Coping strategies were measured with the Carver Brief Coping Questionnaire. Stress was measured with the Perceived Stress Questionnaire. Anxiety and depression were measured with the Hospital Anxiety and Depression Scale. Quality of life was measured with the Inflammatory Bowel Disease Questionnaire.

Results: Disease severity, illness perceptions, maladaptive coping, stress, anxiety, depression and quality of life were significantly correlated with each other among patients with Crohn's disease. Using structural equation modeling to describe the inner relationship of the aforementioned variables, an excellent-fitted model was drawn. (χ²[10]=13.83, P=0.18, χ²/N=1.38, standardized root mean square residual [SRMR] <0.05, root mean square error of approximation [RMSEA] <0.05, goodness of fit index [GFI] >0.97, comparative fit index [CFI] >0.99). Disease severity had a direct influence on illness perceptions. Illness perceptions had a direct influence on stress. Both illness perceptions and stress had direct influences on anxiety, depression, and quality of life, while maladaptive coping did not directly influence anxiety, depression, or quality of life. Stress had a direct influence on maladaptive coping. Quality of life was also directly influenced by disease severity and anxiety.

Conclusion: Interrelationships between disease stimuli, disease perceptions and management and disease outcomes could be found in patients with Crohn's disease. Illness perceptions and stress mediated an individual's disease severity and anxiety, depression and quality of life, while coping strategy was not an applicable mediator.