lack of inclusion pandemic, investigator reluctance, lower than expected incidence of infection

Antimicrobial treatment could be beneficial in patients with ventilator-associated tracheobronchitis (VAT). The hypothesis of this study is that antibiotic treatment for VAT (3 or 7 days), compared with no antibiotic treatment, would reduce the incidence of transition from VAT to ventilator-associated pneumonia (VAP).

The main objective of this randomized controlled multicenter double-blind trial is to assess the efficiency of two durations (3 or 7 days) of antibiotic treatment for VAT, compared with no antibiotic treatment, in reducing the incidence of transition from VAT to ventilator-associated pneumonia (VAP).

Secondary objectives are to determine the impact of two durations (3 or 7 days) of antibiotic treatment for VAT, compared with no antibiotic treatment, on:

• duration of mechanical-ventilation free days
• duration of antibiotic free days
• length of ICU stay
• mortality at day 28 and day 90
• incidence of ICU-acquired colonization related to multidrug resistant (MDR) bacteria
• incidence of ICU-acquired infection related to MDR bacteria
• incidence of ventilator-associated events After informed consent, patients will be randomized (1:1:1) to receive 0 (control group), 3 or 7 days (experimental groups) of antibiotic treatment for VAT

Antibiotic treatment is standardized, based on the time of onset of VAT, and presence of risk factors for MDR bacteria:

• patients with early-onset VAT with no risk factor for MDR bacteria will receive ceftriaxone (2 g iv every 24h).
• patients with late-onset VAT (after day 4 of mechanical ventilation), or with at least one risk factor for MDR bacteria will receive imipenem (1 g iv every 8h), and ciprofloxacin (400 mg iv every 8h) as empirical treatment. When methicillin-resistant Staphylococcus aureus is suspected, linezolid (600 mg iv every 12h) will be added to empirical treatment.

Patients randomized in control group will receive 7 days of placebo, and those randomized in the first experimental arm (3 days of antibiotics) will receive 4 days of placebo.

Inclusion Criteria:

• All adult patients hospitalized in the ICU with a first episode of VAT diagnosed >48 hours after starting invasive mechanical ventilation are eligible for this study.

VAT is defined using the following criteria:

1. absence of new infiltrate on chest X ray
2. two of the three following conditions: fever > 38.5 °C or <36.5, leucocyte count > than 12 000 cells per μL or \