 2. Subjects confirmed to be persistent nasal SA carriers, defined by 3 separate, SA positive cultures from nasal swabs. Two positive cultures should be obtained at screening visits up to 12 weeks prior to inclusion and at least two weeks apart. The final confirmatory culture should be obtained from a nasal swab on the day of admission to the unit day -1. Note: Dosing with XF-73 may commence before the result of the day -1 swab is obtained. If the result is negative, the subject should be withdrawn. 