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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.

Inclusion Criteria:

1. Adults �18 years

2. At least one episode of diverticulitis confirmed by CT scan (or pending confirmation) and a colonoscopy (completed or scheduled) to rule out or screen for other colon pathology concordant with screening guidelines; AND A. History of recurrent uncomplicated diverticulitis without current symptoms (AUD in remission); OR B. Persistent signs, symptoms, and concerns related to diverticular disease �3 months after recovery from an episode of AUD (e.g., excluding irritable bowel syndrome and other conditions in coordination with gastroenterologist)

Exclusion Criteria:

1. Unable or unwilling to return or be contacted for and/or complete research surveys;

2. Currently incarcerated in a detention facility or in police custody (patients wearing a monitoring device can be enrolled) at baseline/screening;

3. Previous operation for diverticulitis

4. Current diagnosis or previous endoscopic or surgical interventions for fistula or stricture or current significant bleeding related to diverticular disease.

5. Right-sided diverticulitis

6. Comorbid or prior surgical conditions that contraindicate elective surgery (e.g., liver failure, renal failure, malignancy, "frozen abdomen")

7. Actively undergoing chemotherapy or radiation for malignancy

8. Immunodeficiency (e.g., absolute neutrophil count