The objective of this clinical trial to evaluate the effectiveness and safety of outpatient treatment without antibiotics compared to outpatient treatment with antibiotics in patients with acute uncomplicated diverticulitis.

The hypotheses are:

• Null Hypothesis (H0): Outpatient treatment without antibiotics in patients with acute uncomplicated diverticulitis is neither safe nor effective and is inferior to outpatient management with antibiotics.
• Alternative Hypothesis (H1): Outpatient treatment without antibiotics in patients with acute uncomplicated diverticulitis is safe, effective, and not inferior to outpatient management with antibiotics.

We compare the rate of complications, therapeutic failure (clinical worsening and readmission) and recurrence between patients who, on an outpatient basis, are administered antibiotics and those who are not.

The patient diagnosed with acute uncomplicated diverticulitis who meets the inclusion criteria is evaluated and examined by a general surgeon. After informing him/her about the pathology, the study will be explained and he/she will be invited to freely participate in it. After accepting and signing the informed consent form, the patient will be included in the study and will be randomly assigned to one of the two treatment arms (outpatient treatment with antibiotics (group A) or without antibiotics (group B).

The surgeon must reassess the patient at 72 hours, with a complete history of the new clinical status, physical examination, and blood tests (with the same parameters). This visit will check treatment adherence and early clinical response. If the patient shows unfavorable progress or clear clinical deterioration, a new imaging test will be considered, and the assigned therapeutic option will be considered a failure. Follow-up will be completed with a face-to-face consultation one month after the episode and another (face-to-face or telematic) at six months.

Inclusion Criteria:

• Patients over 18 years old with clinical and radiological diagnosis of acute sigmoid or descending colon diverticulitis (left-sided acute diverticulitis) not complicated.
• Radiological diagnosis of acute uncomplicated diverticulitis by CT (Modified Hinchey Classification 0-Ia).
• First episode or previous history of acute diverticulitis (both complicated and uncomplicated), with ≥6 months between the last episode and the current clinical presentation).
• Informed consent to participate in the study.

Exclusion Criteria:

• Age >80 years.

• Patients eligible for hospital admission and/or intravenous antibiotic therapy (at the time of diagnosis).

  • Repeated vomiting or oral intolerance.
  • Need for intravenous fluid therapy and/or close monitoring.
  • Peripheral body temperature >38ºC.
  • Deterioration of general condition and/or clinical suspicion of sepsis.

• Significant or decompensated comorbidity: ASA IV Classification (anesthetic risk of American Society of Anesthesiologists).

• Immunocompromised patients: Hematological cause, HIV with low CD4+ levels, immunosuppressive treatment, prolonged corticosteroid therapy, chemotherapy, transplanted or splenectomized patients, predisposing genetic alterations (severe combined immunodeficiency, etc.).

• Oral or intravenous antibiotic therapy 2 weeks before the onset of symptoms for another cause.

• Pregnancy.

• Inflammatory bowel disease (Crohn's disease, ulcerative colitis).

• Lack of social and home support making outpatient treatment and follow-up impossible.