Staphylococcus aureus native arthritis over 10 years.

Objectives: Septic arthritis is associated with significant case fatality and morbidity. Staphylococcus aureus is the most common cause of arthritis. We aimed to analyze the microbiological features of S. aureus causing native arthritis and to investigate their influence on the clinical outcome of the infection.

Patients And Methods: We conducted a retrospective study including all episodes of S. aureus native arthritis between 2005-2015. Phenotypic (antimicrobial susceptibility, β-hemolysis, agr functionality, biofilm formation) and genotypic characteristics (pulsed-field gel electrophoresis, DNA microarrays) were investigated. The primary endpoint was microbiological failure of treatment, including infection relapse, persistence, or attributable death.

Results: Twenty-nine patients were included (65.5% of men, mean age: 59): seven (24.1%) patients presenting with methicillin-resistant S. aureus (MRSA) native arthritis and 19 with methicillin-susceptible S. aureus (MSSA) native arthritis. Treatment failure occurred in seven (26.9%) patients (4/7 patients [57.1%] among MRSA infections vs. 3/19 [15.8%] among MSSA infections). The persistence rate was similar in MRSA and MSSA infections (1/7 vs. 3/19). However, the case fatality was significantly higher in patients with MRSA infection (3/7 vs. 0/19). The most frequent clonal complex (CC) was CC5 (38.1%). MSSA showed higher genetic variability (nine CCs) versus MRSA (3 CCs).

Conclusions: Beyond methicillin resistance, we did not find phenotypic or genotypic factors associated with the poor outcome of S. aureus native arthritis. CC5 was the major CC, showing the higher genetic variability of MSSA versus MRSA.