Introduction: Prediction of flares in UC remains a challenge, with limited analyses on patient (pt)-reported themes associated with onset. The aim of this analysis was to identify the most common pt-reported triggers and symptoms of UC flares. Methods: We reviewed online posts written by pts with UC on 8 public forums in 6 countries between January 1, 2019 and February 14, 2021. Flare-related posts (identified by keywords; Table), including pre- and post-flare posts from the same pts, were captured using Netbase Quid™ artificial intelligence text analytics and natural language processing software. Once identified, all flare-related posts were analyzed and mapped semantically to uncover the most prevalent conversational topics and themes regarding flares to outline the unmet needs and challenges discussed and to examine self-reported triggers of flares. Results: Of > 27,000 pt posts, 12,900 were identified as flare-related. The most common themes identified were treatment experiences, side-effects (28%), and flare symptoms (22%; Figure a). Of the top topics discussed, the most common was emotional / peer support (9.4% of posts), followed by posts on the individual experiences and recommendations of mesalamine (and other oral / rectal suppositories; 8.0% of posts), the most common treatment option discussed, and dietary recommendations (6.0% of posts; Figure b). Pain was a high-impact topic (fatigue and joint pain, 2.4% of posts; Figure b). Stress and anxiety were the most reported triggers of flares (38% of posts), followed by diet (28% of posts; Table), with discussions suggesting pts with UC had difficulty managing external stressors. Depression, anxiety, and fatigue were frequently identified as both triggers for and symptoms of flares. Initial symptoms of flares (e.g., blood in stool; diarrhea and loose stool; stool frequency) were often not distinguished from full flares. Blood in the stool was the most discussed flare indicator (58%; Table). Conclusion: The results of this analysis of pt posts suggest that some frequently discussed triggers and / or symptoms of UC flares, such as depression, anxiety, pain, and sleep disturbances, are not always captured using traditional clinical disease activity measures.1,2 Physicians should consider additional pt-reported outcomes, including emotional and psychological aspects, during the assessment of pts.Figure 1.: a) Top themes and b) top topics in UC patient forum flare-related posts. Flare-related posts, including those from the same author pre- and post-flare, were identified from online posts written by patients with UC on 8 public forums (Afa Crohn RCH, Carenity, Crohn Club Forum, Crohn’s Forum, Deutsche Morbus Crohn/Colitis ulcerosa Vereinigung; Educainflamatoria, HealingWell, Patient) in 6 countries (France, Germany, Italy, Spain, United Kingdom, and United States) between January 1, 2019 and February 14, 2021. Flare-related posts were identified as those containing relevant keywords, including flare, remission, inflammation, cramps, attack, relapse, symptoms, and bloody stool. Flare-related post data were color-coded by a) themes and b) topics; each node represents a post, and connections represent similar language used across the posts. Centrally located nodes represent core concepts, and peripheral nodes represent niche concepts. UC, ulcerative colitis Table 1. - Most discussed flare triggers and initial flare symptoms in patients with UC Ranking Flare triggers (percentage of posts), (N=1,161) Initial flare symptoms (percentage of posts), (N=645) 1 Stress and anxiety (38%) Blood in stool / passing blood (58%) 2 Diet (28%) Diarrhea and loose stool (19%) 3 Smoking cessation (9%) Stool frequency (19%) 4 Antibiotics (9%) Mucus in stool / passing mucus (17%) 5 Bacterial or viral infection (7%)a Pain and cramping (14%) 6 NSAID usage (6%) Fatigue (7%) Flare-related posts, including those from the same author pre- and post-flare, were identified from online posts written by patients with UC on 8 public forums (Afa Crohn RCH, Carenity, Crohn Club Forum, Crohn’s Forum, Deutsche Morbus Crohn / Colitis ulcerosa Vereinigung, Educainflamatoria, HealingWell, and Patient) in 6 countries (France, Germany, Italy, Spain, United Kingdom, United States) between January 1, 2019 and February 14, 2021. Flare-related posts were identified as those containing relevant keywords, including flare, remission, inflammation, cramps, attack, relapse, symptoms, and bloody stool.aPatients who identified bacterial or viral infections as a flare trigger had uniquely low confidence and were unsure about infections being the cause of their triggers.NSAID, nonsteroidal anti-inflammatory drug; UC, ulcerative colitis.