The aim of this study was to compare the prevalence of nasal carrying of SA ST398 strains in community and hospital settings, identify the factors associated with colonization of SA ST398, determine the distribution of imported and acquired cases among SA ST398 hospital cases and characterize the genetic structure of the ST398 SA population involved in colonization.

Staphylococcus aureus (SA) is a ubiquitous bacterium, part of the human commensal flora. The mucosa of the anterior nasal cavities represents the preferred site of colonization of SA. The SA ST398 clone, belonging to CC 398, was initially described as a zoonotic agent initially identified in France and the Netherlands. In fact, ST398 strains are separated into two distinct populations: a methicillin-resistant SA population (SAMR) with notion of contact with animals and a more virulent methicillin-sensitive SA population (SAMS) than its counterpart, isolated from serious human infections and without notion of exposure to farm animals. Recently, we have shown that, in SA bacteremia, all strains of SA ST398 are sensitive to methicillin and that the prevalence of ST398 among all SAMS responsible for bacteremia at Besançon University Hospital increased between 2009 and 2014, increased from 4 to 15%. However, we were unable to study nasal colonization to support the mode of acquisition of SA ST398 (community vs. healthcare acquisition).

For community patients :

Inclusion Criteria:

• the selection criteria for blood donation
• age ≥ 18 years old
• No refusal of the person

Exclusion Criteria:

• None

For hospitalized patients :

Inclusion Criteria:

• age ≥ 18 years old
• hospitalization in one of the services participating in the study
• no refusal of the person

Exclusion Criteria:

• None

For community patients : All patients presenting for blood donation will be included For hospitalized patients, all patients hospitalized less than 48h in a service participating to the study will be enrolled