Colitis from reactivation of established cytomegalovirus (CMV) colonization can complicate the clinical course in patients with an acute flare of ulcerative colitis (UC). Accurate and timely detection of active CMV infection or disease with appropriate anti-viral therapy may reduce complications associated with acute UC flare. Limited information is available on the presence of colonic CMV infection in patients with quiescent ulcerative colitis. Prospective studies on factors associated with reactivation of CMV infection during active UC flare and its impact on disease progression are lacking.

The hypothesis of this study are as follows: 1) CMV infection is prevalent in patients with ulcerative colitis irrespective of disease severity; 2) The degree of immunosuppression directly impacts CMV infection status in patients with ulcerative colitis

This is cross sectional study at St. Paul's Hospital, a tertiary academic teaching hospital. Subjects ages 19 or greater with quiescent ulcerative colitis present for routine elective surveillance endoscopy will be invited for the study.

At enrollment, subjects will be evaluated for clinical and endoscopic disease severity using Mayo score. To be eligible for the study, Mayo score must be <2. Supplemental blood tests, diagnostic test to determine CMV status, physical examination for extra-intestinal manifestation of CMV and inflammatory bowel disease, and surveillance colonoscopy with colonic biopsy will be done.

Patients will be followed longitudinally. Patients will be contacted every three months via their preferred method (telephone or email) until disease flare (clinical partial Mayo Score > 2) or one year from enrolment. Patients will be asked to contact study coordinator when they are experiencing UC flare.

Inclusion Criteria:

• Patients ages 19 or greater with quiescent ulcerative colitis present for routine elective surveillance endoscopy
• At enrolment: clinical partial Mayo score < 2 prior to endoscopic evaluation
• At endoscopy: endoscopic Mayo score < 2

Exclusion Criteria:

• Patient age less than 19
• Clinical partial Mayo score at enrollment ≥ 2
• Endoscopic Mayo score ≥ 2
• Overall Mayo score > 5
• Patients with known current or previous CMV infection
• Patients with HIV, solid organ or bone marrow transplantation, immunoglobulin deficiency, and who are otherwise immunosuppressed for reasons other than treatment of ulcerative colitis, or
• Pregnant patients

All patients with ulcerative colitis presenting for routine elective surveillance endoscopy will be approached for enrolment. Patients will be evaluated by the gastroenterologist at pre-endoscopy clinic visit for eligibility.