Clostridioides Difficile: Understanding Responses and Treatment Effects

The goal of this observational study is to learn how different treatments for Clostridioides difficile infection (CDI) work, and which biological mechanisms are involved in recovery. The study will compare standard antibiotic treatment and fecal microbiota transplantation (FMT). The main questions it aims to answer are: * How do antibiotic treatment and FMT affect treatment outcome in CDI? * How does the gut microbiota change during and after treatment? * Which microbial and metabolic factors are associated with recovery or treatment failure? * How does treatment affect the intestinal barrier, immune response, and patient-reported quality of life? Participants with CDI will receive treatment as part of routine clinical care, either antibiotics or FMT. Researchers will follow participants over time and collect biological samples to study treatment effects. Participants will: * Provide stool samples during the acute infection and during follow-up * Have treatment outcomes assessed at 2 and 8 weeks * Be followed for up to 5 years to study long-term effects * Provide blood and urine samples during follow-up * Provide nasal samples to study potential microbiota changes at distant body sites * Complete questionnaires on symptoms and health-related quality of life * In a subgroup, undergo repeated sigmoid biopsies to study intestinal mucosal healing The results are expected to increase understanding of how FMT and antibiotics lead to recovery in CDI and may support improved and more targeted future treatments.