S385 Global Incidence and Risk Factors of Microscopic Colitis: A Systematic Review

Introduction: Microscopic colitis (MC) is a chronic inflammatory disease of the colon characterized by persistent non-bloody watery diarrhea which significantly impacts the patient’s quality of life. The global incidence of MC is poorly understood and reported, the accuracy of which is essential for public health planning and increasing physician awareness. We conducted a systematic review to summarize existing data on the global incidence rates of MC, explore its regional variations, and identify the strength and validity of pertaining risk factors. Methods: A comprehensive literature search of PUBMED was performed from inception to May 2025 to identify relevant MC studies. Studies with observational design, such as cross-sectional, case-control, population-based cohort, and registry-based studies using local or national health databases, with biopsy-confirmed MC were all eligible. Primary outcomes included the quantitative estimates of incidence rates and secondary outcomes included the quantitative estimates of associated risk factors. Case reports and case series that involved fewer than 10 patients were excluded. Results: A total of 20 studies on risk factors and 22 studies on rates of incident cases from Europe and North America were included in the final analysis. MC was reported to occur at rates between 4.8 and 25.8 out of every 100,000 person-years and in Sweden, Denmark, Switzerland, the United Kingdom, and the USA, with increasing incidence over the past 2 decades. Several consistent patterns were found during the analysis of risk factors. Many studies found celiac disease to be the most common risk factor, with odds ratios (OR) between 7.9 and 22.5. The use of antibiotics, nonsteroidal anti-inflammatory drugs (NSAID), and proton pump inhibitors (PPIs) have been closely liked to MC and the ORs for NSAIDs and PPIs were as high as 20.2 and 10.6, respectively. Other risks such as psychiatric illnesses, smoking, Clostridioides difficile, Campylobacter, and norovirus were also noted. According to the results from large registry studies, female gender and advanced age have also been linked to MC. Conclusion: Our study highlights the fact that MC has become more common worldwide and relates to a combination of factors such as the immune, microbiome, environmental, and drug-related risks. These findings emphasize the need for heightened clinical awareness and prospective research to clarify causal pathways, optimize prevention strategies and inform evidence-based treatment approaches.