Septic arthritis caused by Sphingomonas paucimobilis in an immunocompetent patient.

Septic arthritis is an inflammatory joint disease produced by invasion and multiplication of pathogenic microorganisms. Most cases of septic arthritis are caused by microorganisms of the genus Staphylococcus and Streptococcus. Non-fermenting Gramnegative bacilli (Pseudomonas, Stenotrophomonas, Acinetobacter, and Burkholderia) are a frequent causes of nosocomial infection associated with immunosuppression situations, and Sphingomonas paucimobilis (S. paucimobilis) (formerly Pseudomonas paucimobilis) is also a Gram-negative aerobic fermentor that now emerges as an opportunistic pathogen. We present a case of septic arthritis by S. paucimobilis in a 41year-old man with a history of frequent episodes of hyperuricemia and gout in his left knee. In the past year, he presented several episodes of acute monoarthritis treated with nonsteroidal antiinflammatory drugs, colchicine, and intraarticular infiltration of triamcinolone. The patient presented with symptoms of pain and swelling of left knee which had lasted for 3 months without fever. Physical examination showed: temperature 36.5 ◦C and left knee arthritis with preserved but painful active and passive mobility. Arthrocentesis was performed, resulting in inflammatory synovial fluid, without evidence microcrystals under the polarized light microscope. The fluid was sent to the microbiology department in a sterile syringe and blood culture bottles for aerobic and anaerobic culture. Gram stain showed abundant polymorphonuclear leukocytes and intracellular Gram-negative bacilli, and the culture-negative bacilli isolated were identified as S. paucimobilis by ID32GN Api (bioMerieux, Marcy L’etoile 3. France), sensitive to beta-lactams, aminoglycosides, quinolones, and cotrimoxazole. Laboratory analysis upon the patient’s admission showed 8070 leukocytes/L (70% neutrophils and 30% lymphocytes), erythrocyte sedimentation rate of 42 mm the first hour and CRP 8.04 mg/dl. CBC, coagulation, and biochemistry were normal. Echocardiogram was normal and Xrays showed a slight increase in soft tissue suprarrotulian density, indicative of effusion; the CT with intravenous contrast observed loosening of articular recesses, with slight enhancement of the synovium. Daily articular drainage was performed and the patient was treated with ceftazidime (6 g/24 h) plus gentamicin (240 mg/24 h),