The investigators purpose is to demonstrate that a short antibiotic therapy (8 days) for postoperative peritonitis brings an increased number of antibiotic-free days over a 28 days period when compared to conventional (15 days) treatment.

This is a prospective randomized study involving 25 centers. Our goal is to demonstrate in the course of postoperative peritonitis that a short antibiotic therapy (8 days) compared to conventional antibiotic treatment (15 days) decreases the duration of exposure to antibiotics over a 28 days period . Patients admitted in ICU, operated for postoperative peritonitis and receiving an adequate antibiotic therapy will be identified and after informed consent is obtained will be randomized to receive a short course of antibiotic therapy (8 days) or a long course of antibiotic therapy (15 days). The primary endpoint is the number of antibiotic-free days at D28 after inclusion (analysis of superiority) . Secondary endpoints include mortality at D45 after inclusion (analysis of equivalence), the occurrence of relapse of infection, success rate of clinically and microbiologically evaluable patients, and emergence of multidrug resistant microorganisms in clinical isolates or hygiene samples. Patient data through day 45 following the initial intervention or until hospital discharge will be tracked.

Inclusion Criteria:

The eligible patients have to fulfill all the following criteria

1. patients admitted in intensive care unit
2. in the 24 hours following surgery for postoperative intra-abdominal infection (defined as gross pus or purulent effusion within the peritoneal cavity or in one or several collections). Postoperative infection will be defined as an infection observed in a delay of 60 days following a procedure (endoscopy, surgery (abdominal, urologic, gynecologic or vascular surgery or any surgery performed in the peritoneal or retroperitoneal space) or interventional radiology)
3. having peroperative microbiologic samples collected
4. receiving an empiric antibiotic therapy initiated within the first 24 hours after completion of surgery
5. with a written informed consent from the patient or the relative or the legal representative or with an emergency consent

Non-inclusion criteria :

Patients with one of the following criteria are eligible for the study :

1. age<18
2. pregnancy
3. Duration of stay following inclusion <72 hours
4. neutropenia (PMN<500/mm3) due to chemotherapy or hematological disease
5. AIDS stage C
6. Immunosuppressive therapy or prolonged steroid therapy (≥0.5 mg/kg/d of prednisone or equivalent >1 month
7. Bowel perforation following endoscopy treated in a delay <6 hours after injury
8. Uterine perforation following a surgical procedure treated in a delay <6 hours after injury
9. Moribund patient (SAPS II score >65 within 12 hours preceding inclusion)
10. Limitation of treatment previously decided
11. Surgery considered as non curative by the surgeon
12. Patient included in another clinical trial evaluating an antimicrobial agent

Secondary exclusion criteria:

Among the eligible patients, those who have one of the following criteria will be excluded

1. Negative culture of the peritoneal fluid
2. Peritoneal culture exclusively fungal
3. Inadequate empiric antibiotic therapy (not targeting all the microorganisms cultured from peritoneal or blood cultures) within 24 hours after surgery
4. Death between D1 and D8