Gram and acridine orange staining for diagnosis of septic arthritis in different patient populations.

PURPOSE: The sensitivity of Gram staining is known to be suboptimal for the diagnosis of native joint septic arthritis. We lack information about the accuracy of Gram compared to other microscopic staining techniques for predicting infection in different patient populations. METHODS: This was a cohort study with cost evaluations at the Orthopaedic Service of Geneva University Hospitals (January 1996-October 2012). RESULTS: Among 500 episodes of arthritis (196 with immunosuppression, 227 with underlying arthroplasties and 69 with gout or other crystals in synovial fluid), Gram staining revealed pathogens in 146 episodes (146/500, 29 %) or in 146 of the 400 culture-positive episodes (37 %). Correlation between the Gram and acridine staining of the same sample was good (Spearman 0.85). Overall, the sensitivity, specificity, positive predictive value and negative predictive value of Gram stain for rapid diagnosis of septic arthritis was 0.37, 0.99, 0.99 and 0.28, respectively, compared to microbiological cultures. Quite similar values were recorded across the different patient subpopulations, in particular for sensitivity values that were 0.33 for patients with prosthetic joint infections, 0.40 for immunosuppressed patients, 0.36 for patients under antibiotic administration and 0.52 for patients with concomitant crystalline disease. CONCLUSIONS: The sensitivity of Gram or acridine orange staining for a rapid diagnosis of episodes of septic arthritis is suboptimal compared to microbiological culture, regardless of underlying conditions, immunosuppression or antibiotic therapy. The sensitivity in the presence of synovial fluid crystals is moderate. Acridine orange and Gram stains are equivalent.

Remission after treatment of osteoarticular infections due to Pseudomonas aeruginosa versus Staphylococcus aureus: a case-controlled study.

PURPOSE: Osteoarticular infections due to methicillin-susceptible Staphylococcus aureus (MSSA) or its methicillin-resistant variant (MRSA) are feared due to treatment failures. According to clinical experience, Pseudomonas aeruginosa may reveal less long-term remission than S. aureus. METHODS: A case-controlled study comparing outcomes of osteoarticular infections due to P. aeruginosa vs S. aureus was performed at Geneva University Hospitals. RESULTS: A total of 111 S. aureus (including 37 MRSA) and 20 P. aeruginosa osteoarticular infections were analysed in 131 patients: arthroplasties (n = 38), fracture fixation devices (n = 56), native joint arthritis (n = 7) and osteomyelitis without implant (n = 30). The median active follow-up time was 4 years. The patients underwent a median number of two surgical interventions for P. aeruginosa infections compared to two for S. aureus (two for MRSA), while the median duration of antibiotic treatment was 87 days for P. aeruginosa and 46 days for S. aureus infections (58 days for MRSA) (all p > 0.05). Overall, Pseudomonas-infected patients tended towards a lower remission rate than those infected with S. aureus (12/20 vs 88/111; p = 0.06). This was similar when P. aeruginosa was compared with MRSA alone (12/20 vs 30/37; p = 0.08). In multivariate logistic regression analyses adjusting for case mix, odds ratios (OR) for remission were as follows: P. aeruginosa vs S. aureus [OR 0.4, 95% confidence interval (CI) 0.1-1.2], number of surgical interventions (OR 0.6, 95% CI 0.5-1.0) and duration of antibiotic treatment (OR 1.0, 95% CI 1.0-1.0). CONCLUSIONS: Despite a similar number of surgical interventions and longer antibiotic treatment, osteoarticular infections due to P. aeruginosa tended towards a lower remission rate than infections due to S. aureus in general or MRSA in particular.