Background Chlamydia trachomatis and Neisseria gonorrhoeae can cause infectious proctitis, which macroscopically cannot be distinguished from haemorrhagic proctosigmoiditis (HP) caused by inflammatory bowel disease. In Denmark, general practitioners are advised to consider whether patients presenting with proctitis symptoms might have a sexually transmitted infection (STI). However, there is no requirement for STI testing before referring the patient to a specialised department. At specialised departments, it is not standard practice to systematically inquire about sexual risk behaviour or to test for Chlamydia and Gonorrhoea. As a result, there is no data on how many patients diagnosed with HP due to chronic inflammatory bowel disease are also positive for an STI, either as the sole cause or as a contributing factor to their inflammation. Chlamydia and Gonorrhoea are the most common causes of symptomatic, sexually transmitted proctitis and are increasingly prevalent in Denmark. Materials and methods Since diagnosing haemorrhagic proctosigmoiditis requires an endoscopy (sigmoidoscopy or colonoscopy), all newly diagnosed patients will undergo such an examination. Moreover, an endoscopy is often performed in individuals with refractory proctosigmoiditis. If inflammation is observed up to 35 cm from the anal opening, an additional swab will be taken during the procedure to test for Chlamydia and Gonorrhoea using standard PCR techniques. If the swab is not taken during the endoscopy, it will be collected during a follow-up outpatient visit. The tests will be analysed immediately at the Department of Microbiology, Aarhus University Hospital. Over 24 months, the investigators will examine all patients diagnosed with proctosigmoiditis at the Department of Liver, Digestive, and Gastrointestinal Diseases at Aarhus University Hospital (AUH), Viborg/Silkeborg Regional Hospital, Horsens Regional Hospital, Gødstrup Regional Hospital and Randers Regional Hospital. This includes patients with inflammation extending from the anal opening to 35 cm proximally, as well as those with treatment-refractory proctosigmoiditis. All patient data will be prospectively collected through Region Midt EPJ, Denmark's electronic medical record system, and registered in a REDCap database. The tested patients will undergo standard follow-up at their respective departments. Supple-mentary, patients who test positive for Chlamydia or Gonorrhoea will be offered treatment at the Venereology Outpatient Clinic, Aarhus University Hospital. If they are only on 5-ASA treatment and it is found reasonable to pause their treatment, their IBD treatment will be paused during treatment for STI. The studied patients will form a prospective cohort, and their disease progression, including the extent of haemorrhagic proctitis and current medication, will be recorded. Endpoints Primary endpoint: \- Prevalence of Chlamydia and Gonorrhoea in our cohort of individuals with suspected haemorrhagic proctitis. Secondary endpoints: * Prevalence of Chlamydia and Gonorrhoea across gender * Prevalence of Chlamydia and Gonorrhoea across age groups * Prevalence of Chlamydia and Gonorrhoea depending on time for diagnosis * Frequency of clinical remission of proctitis after treatment with STI-related antibiotics * Differences in the frequency of clinical remission between those with a negative or positive STI test at inclusion