Surgical removal of the appendix, called an appendectomy, has been the standard of care for treatment of appendicitis for over 120 years, but treatment with antibiotics instead has been proposed as an alternative. First used in the 1950s with good results, antibiotics for appendicitis were commonly used on submarines in the 1960s-1980s and in other cases where surgery was too risky to remove an infected appendix. Before CODA, six randomized trials in Europe over the last 20 years trialed the use of antibiotics (1, 2, 3, 4, 5, 6). These studies found that antibiotics were successful in treating appendicitis for most patients, but approximately 1 in 4 people underwent appendectomy by 1 year (37% at 5 years).

These prior trials excluded patients with evidence of an appendicolith, a small stone at the base of the appendix, and those suspected of having more severe disease. Most of these previous studies were small and included mostly younger patients. As a result, many questions remained, including whether patients with appendicitis seen at healthcare practices in the United States would have similar results. Perhaps because of these remaining questions and skepticism among surgeons, as recently as 2014, more than 95% of patients with appendicitis in the United States were treated with an appendectomy.

Our Study

CODA is the largest randomized trial comparing appendectomy to antibiotics for the treatment of appendicitis in the U.S. It focused on both clinical outcomes—broadly agreed, measurable changes in health—as well as the patient-reported outcomes (PROs) that matter most to patients.

Study participants may have had surgery or they may have taken antibiotics. Most patients had their treatment decided randomly, with an equal chance of getting either treatment. The study also included patients who did not want their treatment decided randomly. Results of this study will help patients better understand the difference between surgery and antibiotics. It will also tell us if certain patients would benefit more from one treatment than the other and help nearly 300,000 Americans each year make an important healthcare decision.

Past studies have not evaluated whether or not the benefits of possibly avoiding surgery outweighed the risks and anxiety patients may feel about future episodes of appendicitis. No studies to date have compared the impact of these two appendicitis treatments on the overall patient experience or included PROs in addition to clinical outcomes. In short, the studies to date have not asked “Is antibiotics first as good a treatment for me as appendectomy?” This is what the CODA trial aimed to address.

Coordinating Institution

The University of Washington’s Surgical Outcomes Research Center (SORCE) in Seattle, Washington, leads the Clinical and Stakeholder Coordinating Centers. The UW Center for Biomedical Statistics serves as the Data Coordinating Center.


Research reported in this publication was funded through a Patient-Centered Outcomes Research Institute (PCORI) Award (1409-24099). The statements in this website are solely the responsibility of the authors and do not necessarily represent the views of PCORI, its Board of Governors, or Methodology Committee.

Learn about the study team and participating sites.