Surgical site infections in orthopaedic surgery are a major problem. Decolonization has been suggested to reduce infection rates. The study was designed as a prospective, controlled, randomized, single-blinded trial to assess the influence of a decolonization procedure in S. aureus and non - S. aureus carriers. In this trial the 2 - year outcome in the subpopulation of prosthetic elective orthopaedic surgery will be evaluated.

To verify the main hypothesis, a prospective controlled randomized interventional trial with 2 parallel groups of patients of the Sonnenhof hospital undergoing an elective knee- or hip implant surgery was designed. A superiority framework for the decolonization procedure was used. All patients planned for such a procedure will be recruited during preoperative consultation by the orthopedic surgeons or by post and phone. Written informed consent will be obtained at this occasion. Study participants were screened 2-4 weeks prior intervention for nasal S. aureus colonization.

Study participants were allocated on a 1:1 basis either to an intervention or to a control group, but prosthesis implantation was not defined as randomization criteria in the initial trial. Randomization was stratified for important risk factors of SSI; procedure type (upper extremities and pelvic/hip, spine, knee and foot) and ASA-criteria (I, II, III -V). Stratification-groups were chosen in function of SSI's rate and expected number of operations/year. Randomization list were generated by the CTU and allocation was concealed using central randomization that was implemented in the REDCap data entry system.

One week prior to hospitalization patients in the intervention group received a decolonization kit by mail with instructions to apply mupirocin ointment 2% (BACTROBAN Nasal ong 3g, GSK) in each nostril 30mg (which corresponds approximately the same amount as the volume of a pea) twice a day and to shower daily (starting with the face, then from top to bottom the whole body emphasizing especially on nose, axillaries and pelvic region and then rinse. In a second time starting with the hair and then repeat the whole body. Dry with a proper towel (one for the 5 days)) with 25ml chlorhexidine gluconate soap, (Lifo-Scrub sol 4 % 500ml, B. Braun) during 5 days prior surgery. For non S. aureus carriers only skin cleansing without intranasal mupirocin application was used. This dosing schedule, mode of administration and treatment periods correspond to the allowed and recommended standards of Swissmedic and were not modified in this trial. Decolonization occured before hospitalization, as a fully completed course before surgery has been more effective. In some of the previous trials decolonization took place only at the beginning of hospitalization. The decolonization procedure was only completed after surgery had taken place and this possibly affected the results.

For practical reasons the use of a placebo kit within the control group abandoned. Operators, who are also the outcome assessors, will be blinded for either the carrier status or the decolonization procedure. Study participants will be told not to inform surgeons about performed decolonization procedure.

The incidence of PJI at two years in the intervention and control group will be assessed by phone interview.

Inclusion Criteria:

• older than 16 years
• planned elective orthopedic procedure
• Decolonization protocol can be performed timely

Exclusion Criteria:

• No orthopedic prosthetic surgery planned
• Allergy to mupirocin or chlorhexidine
• Presence of a nasal foreign body
• No informed consent
• undergoing treatment/surgery for a documented infection
• already participating in the study

Participants are not told colonization status or study arm. Outcome Assessor are not informed as well on this informations.