In patients on mechanical ventilation, it is not known whether the identification of S. aureus in LRT samples improves the performance of its nasal detection.

To assess the MSSA or MRSA carrier status of patients requiring mechanical ventilation for more than 48 hours after major heart surgery: comparing the performance of the diagnostic technique Xpert® SA Nasal Complete assay in nasal swab and LRT samples.

Patients undergoing heart surgery require ventilation for more than 48 hours. These patients, placed on mechanical ventilation for a median of 7 days, will be followed weekly until their discharge from hospital. We estimate we will need 500 determinations.

Samples will be obtained according to usual clinical practice. Thus, rather than discarding a sample, it will be subjected to the two laboratory diagnostic techniques (conventional culture and the Xpert® assay). No patient will be subjected to any procedure outside that of routine clinical practice.

Patient with a tracheal tube in whom nasal and LRT secretions can be simultaneously obtained. Patients may also be included if LRT samples can be obtained via a different approach (tracheostomy, fibrobroncoscopy etc.).

Inclusion Criteria:

• Adults (≥ 18 years)
• Signed Informed consent
• Patient admitted to the HS-ICU before or after undergoing heart surgery
• Patient on mechanical ventilation for >2 calendar days on the date of event (suspicion of LRT infection) ), taking the day of ventilator placement as day 1
• Patient with a tracheal tube in whom nasal and LRT secretions can be simultaneously obtained. Patients may also be included if LRT samples can be obtained via a different approach (tracheostomy, fibrobroncoscopy etc.).

All patients admitted to the Heart Surgery-ICU