An interventional study of Partial Colectomy and Medical Management in Diverticulitis, sponsored by University of Washington. Active, not recruiting at 29 sites in United States. Open to participants aged 18 Years and older. Per ClinicalTrials.gov, last updated 2026-02-19.
Sponsored by University of Washington · Not applicable, Interventional, and Treatment
The COSMID (Comparison of Surgery and Medicine on the Impact of Diverticulitis) trial is a pragmatic, patient-level randomized superiority trial of elective colectomy vs. best medical management for patients with quality of life (QoL) limiting diverticular disease. A parallel observational cohort will include those who are disinclined to have their treatment choice randomized, but are willing to contribute information about their outcomes. The goal of the COSMID trial is to answer the question: For patients with QoL-limiting diverticular disease, is elective colectomy more effective than best medical management? The hypothesis being tested in the COSMID trial is that patient-reported outcomes (PROs) among patients in the surgery arm will be superior to those in the best medical management arm.
For over 50 years, professional society recommendations for the management of uncomplicated diverticulitis included early elective surgery to prevent the need for an emergency operation and avoid the risk of colostomy. Over the last 15 years the notion that a patient must have a certain number of episodes of acute uncomplicated diverticulitis (AUD) before undergoing elective colectomy has changed dramatically. This was, in part, due to studies showing that emergency surgery for complicated disease is much more likely to be needed during the first episode of diverticulitis, making the notion of prophylactic elective colectomy for AUD less relevant. Furthermore, clinicians realized that most recurrent episodes of AUD could be managed with outpatient antibiotics alone and that "best medical management" - including fiber supplementation, mesalazine, rifamycin and probiotics - could reduce symptoms between episodes of AUD. All of the components of best medical management have some, albeit limited, evidence of effectiveness, most in improving symptoms rather than reducing the risk of recurrence and are relatively safe and inexpensive. Best medical management is far less invasive than elective surgery but infrequently prescribed the US, in part because of limited insurance coverage. Alternatively, resection removes the diseased segment of colon, does relieve symptoms and decreases the risk of recurrence.
In 2014, guidelines from the American Society of Colorectal Surgeons (ASCRS) abandoned "episode count" as an indication for surgery in patients with AUD and instead recommended individualizing the decision to operate for AUD based on the "effects on lifestyle (professional and personal) of recurrent attacks". Decision making about surgery in patients with lingering symptoms after recovery from an episode of AUD has not been the specific focus of an ASCRS guideline, but recommendations about elective surgery emphasize individualizing decision making based on the overall impact of the disease on the patient.These recommendations for individualization of treatment based on the quality of life (QoL) impact of recurrent AUD and lingering symptoms highlight the decision that hundreds of thousands of people now have to make each year. Based on the effect of the disease on their QoL they must choose between two very different treatment options: elective colectomy vs. best medical management. While the recommendation to individualize treatment based on the QoL impact is a step forward in advancing patient-centered care, the comparative effectiveness of these two treatments on symptoms and QoL has not been well studied.
This will be a multi-site, open randomized trial in which participants with either recurrent AUD or lingering symptoms after an episode of AUD are randomized to one of two initial treatment strategies, elective segmental colectomy (performed laparoscopically when possible) and best medical management.
125 studies on the registry are indexed under Diverticulitis; 22 are open to participants now.
This study's planned enrollment of 255 is above the median of 120 across 63 interventional studies indexed under Diverticulitis.
Browse Diverticulitis studies →University of Washington is the lead sponsor of 1,433 studies on the registry; 225 are open to participants now.
Of its 158 completed or terminated interventional studies of FDA-regulated products, 136 (86%) have results posted.
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Go through the criteria one by one — yes, no or not sure — and take the list to your doctor or the study team. Kept in this browser only.
Exclusion Criteria:
Underlined terms in the criteria open these too. Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
The number of neutrophils, white blood cells that help fight infection, in a given amount of blood. Too few raises the risk of infection.
It is a count, not a percentage of the white cells. Limits are written in units that mean the same: ≥ 1.5 × 10⁹/L is ≥ 1,500 per mm³ (µL). Each lab has its own reference range.
A weakened immune system. It can come from an illness, such as HIV or some blood cancers, or from medicines that turn the immune system down, for example after an organ transplant or for an autoimmune disease; steroids at higher doses count.
Read whether the line is about a condition or about medicines, and which medicines and doses it means.
Anti-inflammatory medicines such as prednisone, prednisolone and dexamethasone — not the anabolic steroids used for muscle.
Studies differ in what they allow: check which steroid medicines, routes (tablets, injections, creams, inhalers, eye drops) and doses this study accepts.
The number of CD4 cells, a type of white blood cell, in a given amount of blood. It is used to follow how well the immune system is doing in HIV.
Malignancy means cancer. Criteria about another or earlier malignancy ask whether you have had a different cancer, usually within a set number of years.
Some are commonly allowed, such as treated skin cancers other than melanoma and early cancers removed completely — check the exceptions this study lists.
A drug or device being studied in a clinical trial.
It may be new, or already approved and being studied for another use, dose or form. Criteria often leave out people who took part in another study of one within a recent period, commonly 30 days or five half-lives.
Absolute neutrophil count (ANC)
The number of neutrophils, white blood cells that help fight infection, in a given amount of blood. Too few raises the risk of infection.
It is a count, not a percentage of the white cells. Limits are written in units that mean the same: ≥ 1.5 × 10⁹/L is ≥ 1,500 per mm³ (µL). Each lab has its own reference range.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Immunosuppression
A weakened immune system. It can come from an illness, such as HIV or some blood cancers, or from medicines that turn the immune system down, for example after an organ transplant or for an autoimmune disease; steroids at higher doses count.
Read whether the line is about a condition or about medicines, and which medicines and doses it means.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Corticosteroids (steroids)
Anti-inflammatory medicines such as prednisone, prednisolone and dexamethasone — not the anabolic steroids used for muscle.
Studies differ in what they allow: check which steroid medicines, routes (tablets, injections, creams, inhalers, eye drops) and doses this study accepts.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
CD4 count
The number of CD4 cells, a type of white blood cell, in a given amount of blood. It is used to follow how well the immune system is doing in HIV.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Cancer (malignancy)
Malignancy means cancer. Criteria about another or earlier malignancy ask whether you have had a different cancer, usually within a set number of years.
Some are commonly allowed, such as treated skin cancers other than melanoma and early cancers removed completely — check the exceptions this study lists.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Investigational drug or device
A drug or device being studied in a clinical trial.
It may be new, or already approved and being studied for another use, dose or form. Criteria often leave out people who took part in another study of one within a recent period, commonly 30 days or five half-lives.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Elective segmental colectomy for diverticular disease involves removal of the segment of colon (most commonly sigmoid and/or left colon) where there has been disease identified by computed tomography imaging or colonoscopy. Elective colectomy usually removes the affected colon along with adjacent segments that have diverticula, with a primary anastomosis performed to reestablish bowel continuity. Most surgeons now perform the procedure using a laparoscopic approach, when possible, and sometimes use a temporary, protective stoma if the re-connection is considered high-risk. The technique for laparoscopic resection is not specified by the protocol (allows for any number of laparoscopic port sites, all incision types, hand-assistance and robotic) with details of the technique recorded. If randomized to elective colectomy, patients will be encouraged to undergo the procedure within 6 weeks of assignment.
Procedure: Partial Colectomy
Medical management for diverticular disease has been used for over 30 years and includes a set of interventions, all components of which have been the subject of small, but often positive trials. All patients randomized to medical management or who select it as their treatment in the observational cohort will view a video (provided in English and Spanish) that explains each element of the medical management "toolbox": diet and exercise recommendations, fiber supplementation (e.g., augmenting dietary fiber or over the counter fiber supplements), with mesalazine tablets or suppositories, probiotics and rifamycin. In consultation with their physician, they will be recommended to a regimen of diet and exercise and fiber supplementation. Clinicians will be asked to consider rifamycin (dose/frequency) for those with AUD who are not responding to diet and exercise and mesalazine (dose/frequency) for those with lingering symptoms who are not responding to diet and exercise.
Other: Medical Management
Most partial colectomies are performed using a laparoscopic approach, when possible, and surgeons sometimes use a temporary, protective stoma if the re-connection is considered high risk.
Patients will be offered a varying combination of tools from the best medical management "toolbox" (diet and exercise, fiber supplementation/probiotics, and rifamycin/mesalazine) depending on what they have already tried. Based on the "evidence-based best medical toolbox" clinicians will be asked to consider rifamycin (dose/frequency) for those with AUD who are not responding to diet and exercise and mesalazine (dose/frequency) for those with lingering symptoms who are not responding to diet and exercise.
Patient-reported quality of life as measured by Gastrointestinal Quality of Life Index (GIQLI)
A 36-item questionnaire assessing 5 domains: GI symptoms, physical function, emotional well-being, social well-being, and perception of medical treatment measured by a single item question. Each item has 5 response choices (i.e., all of the time, most of the time, some of the time, a little of the time, never). In addition, the measure produces an overall quality of life score (0-144) where higher numbers indicate greater QoL.
Time frame: Mean GIQLI at 6, 9, and 12 months following randomization to treatment
Diverticulitis Quality of Life (DV-QoL) instrument
A 17-item questionnaire including a pain scale and questions about about physical, emotional, and social effects of diverticulitis over the past 2 weeks, with a total score ranging from 0 (best) to 10 (worst) with higher scores reflecting worse quality of life effects from diverticulitis.
Time frame: Baseline, 12 months, 24 months
Patient-Reported Outcomes Measurement Information System (PROMIS) Global Health measure
A 10-item instrument measuring domains that can be scored into a Global Physical Health component and Global Mental Health component. Each item includes 5 response choices, with the exception of the common 11-point pain intensity item ("How would you rate your pain on average?" with 0=no pain and 10=worst imaginable pain), where higher scores reflect more severe symptoms/impairment.
Time frame: Baseline; 6, 12, 24, 36 months
Decision Regret Scale
A 5-item validated questionnaire that measures regret among patients following a specific treatment decision. Scores range from 0-100 and higher scores reflect higher levels of regret. While developed for use in patients undergoing treatment for cancer, the questions are general in nature and adaptable to diverse clinical experiences.
Time frame: 6 and 36 months
Work Productivity and Activity Impairment instrument
A 6-item instrument used to measure the effect of general health and symptom severity on work productivity and regular activities during the past seven days. Scores are calculated applying algorithms to the five numerical responses, three of which are continuous variables (hours) and two of which are a scale from 0-10, then converting to a percentage, with higher WPAI scores indicating greater impairment and less productivity. The WPAI measures work productivity loss due to general health or a specified health problem. This questionnaire has been validated for use in many gastrointestinal diseases, including gastroesophageal reflux disease, irritable bowel syndrome, and Crohn's disease.
Time frame: Baseline; 6, 12, 18, 24, 30, 36 months
Plan to share: Yes — Data and results from this proposal stand to develop research that may have a lasting value beyond the term of the award and will be archived and preserved, supporting access to third parties interested in replication and verification of our results and data reuse by other investigators planning future studies. We will prepare and share a complete, cleaned, de-identified copy of the final dataset used in conducting the final analyses upon which the accepted primary study publication is based. The final dataset will include participants' treatment group assignment, demographics and patient reported outcomes (GIQLI survey). Data collected on clinical variables will also include: NSQIP-defined complications major complications, dates and details of healthcare utilization including hospitalizations, length of stay, use of imaging, colectomy details and associated pathology results, and medication use.
Supporting information: Study protocol, Statistical analysis plan, Informed consent form
Time frame: We intend to prepare and share a complete, cleaned, de-identified copy of the final dataset used in conducting the final analyses upon which the accepted primary study publication is based, timing dependent on funding. Our goal is that data will be made available no later than the end of the completion of the funded project period for the parent award or once a manuscript (or manuscripts) covering the primary study aims have been published, whichever is earlier. A complete study data set will be permanently archived and available through the PCODR as described above.
Access criteria: Aggregate clinical trials data from all arms of the study will be available in ClinicalTrials.gov, along with related metadata. All other data described above in the "data to be shared" section will be available through the PCODR and preserved through methods which are in accordance with standard practice. There are no anticipated factors or limitations that will affect the access, distribution or reuse of the scientific data generated by the proposal. Data will be shared as allowed by the participant's informed consents and in accord with IRB approval.
This study is active, not recruiting, as verified in Feb 2026. You cannot join it, but the record below documents what was studied.
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