Surgical Site Infections in Orthopaedic Surgery Demonstrate Clones Similar to Those in Orthopaedic Staphylococcus aureus Nasal Carriers.

BACKGROUND: Staphylococcus aureus is the main microbial pathogen in orthopaedic infections, and it adds considerable extra costs to the national health-care system each year. Nasal carriers of Staphylococcus aureus have an increased risk of invasive disease, including surgical site infection. The purpose of the present study was to investigate whether the Staphylococcus aureus carrier clones found in patients undergoing elective orthopaedic surgery were the same as the clones found in isolates from orthopaedic patients with Staphylococcus aureus surgical site infections. METHODS: Patients admitted for elective orthopaedic surgery underwent nasal cultures for Staphylococcus aureus. Further, orthopaedic patients with a deep surgical site infection caused by Staphylococcus aureus were characterized using the same genotyping methods: multilocus sequence typing and staphylococcal protein A typing. RESULTS: Multilocus sequence typing revealed a large number of genotypes in the two populations. However, 85% of nasal carriers and 90% of surgical site infection isolates could be classified into the same four multilocus sequence typing clonal complexes. The risk of Staphylococcus aureus surgical site infection in nasal carriers compared with non-carriers was 5.8 times higher (95% confidence interval, 1.5 to 23.1 times). Of the nasal carriers, 6.3% (95% confidence interval, 1.7% to 10.9% [seven of 111 patients]) developed a deep Staphylococcus aureus surgical site infection, and all but one patient had identical genotypes in the nasal and surgical site infection isolates. CONCLUSIONS: Staphylococcus aureus isolates from nasal carriers and patients with surgical site infection clustered into the same few multilocus sequence typing clonal complexes. This finding confirms the existence of some commonly occurring Staphylococcus aureus clones in different population groups within a geographically restricted area. The almost complete individual concordance between Staphylococcus aureus genotypes in carriers who developed a deep surgical site infection strongly supports transmission from the nose, skin surfaces, and other endogenous body regions as a possible route. CLINICAL RELEVANCE: Surgical site infections might be more frequently caused by endogenous transmission than was previously assumed. Perioperative preventive efforts must focus more on this route to further decrease the risk of postoperative orthopaedic infections.

USA300 methicillin-resistant Staphylococcus aureus in Norway.

Moen AEF*, Tannaes TM, Leegaard TM. USA300 methicillin-resistant Staphylococcus aureus (MRSA) in Norway. Community-associated methicillin-resistant S. aureus USA300 is known for its ability to disseminate and colonize and the clone has been detected globally. We studied the most populated area in Norway in search for the strain and for signs of endemic establishment. Strain typing techniques such as spa-, SCCmec- and dru-typing, pulsed-field gel electrophoresis and detection of USA300 molecular markers, lukS/F-PV and arcA, were performed. USA300 has been present in the study area since 2003 and has increased in incidence in parallel with the total MRSA incidence. Most USA300 isolates were found in the community, but isolates were also detected in health care institutions.