Septic arthritis due to Rothia mucilaginosa.

TL;DR: A 73-year-old woman presented with pain and swelling of the right knee, which had developed over the past 2 days, and a presumptive diagnosis of septic arthritis was made.

Abstract: A 73-year-old woman presented with pain and swelling of the right knee, which had developed over the past 2 days. A review of her medical history revealed type 2 diabetes mellitus and arterial hypertension. Rheumatoid arthritis that affected fingers and toes had been diagnosed more than 30 years previously, for which 12.5 mg prednisone daily had been prescribed. Due to knee pain, the patient had received a series of intra-articular injections with corticosteroids and local anaesthetics into the right knee at 2 and 6 days and 12 weeks before admission. Radiation synovectomy of the right knee had been performed 6 months and 3 and 9 years prior to admission. Clinical examination of the right knee showed joint pain, swelling, warmth, and restricted movement. Walking was impossible. Other joints were unremarkable. Radiographic assessment revealed advanced osteoarthritis (Fig. 1) of the right knee. Blood laboratory studies revealed elevated leukocytes (14,000/ll) and a normal C-reactive protein level (2.6 mg/l). A presumptive diagnosis of septic arthritis was made. The patient was admitted to the ward, and intravenous clindamycin 600 mg three times daily was administered empirically. Within the following 6 days the swelling progressed significantly and the C-reactive protein level rose to 112 mg/l. Drainage of the right knee was performed, and 80 ml of purulent fluid was aspirated. Microbiological examination of the aspirate revealed a leukocyte count of 42,000 and the presence of Gram-positive cocci in clusters that were subsequently identified as R. mucilaginosa by VITEK II and confirmed by complete 16S rRNA gene sequencing (99% homology with R. mucilaginosa strain DY-18). Minimum inhibitory concentrations, as determined by the E-test, demonstrated sensitivity to ampicillin (0.25 mg/l), cefotaxime (0.5 mg/l), and moxifloxacin (0.19 mg/l) and resistance to clindamycin (2 mg/l). Once the susceptibility results were known, the antimicrobial treatment was changed to moxifloxacin 400 mg once daily. The clinical condition of the patient improved promptly, but the patient recovered slowly. Arthroscopic examination revealed empyema, synovitis, cartilage loss, and meniscal lesions. Several arthroscopic irrigations and synovectomy were performed. Microbiological examination of subsequent samples did not reveal microbial presence. After 2 weeks, the antimicrobial treatment was switched to ampicillin plus sulbactam 375 mg twice daily and continued for 7 weeks. Knee pain and synovial effusion receded and the patient was able to walk using a walking frame. A. J. Kaasch H. Seifert Institute for Medical Microbiology, Immunology and Hygiene, Cologne University, 50935 Cologne, Germany