[An elderly case with group B streptococcal bacteremia, subcutaneous abscess and reactive polyarthritis].

We report a 77-year-old woman with Group B streptococcal bacteremia, subcutaneous abscess and reactive polyarthritis. Two years previously she suffered from atrial fibrillation and osteoarthritis of the knee. After she was admitted for treatment of the knee joint with hyaluronate sodium, she complained of pain in the left shoulder and both knees. Pyogenic arthritis was suspected and administration of cefazolin was started immediately after blood culture. One set of blood cultures showed Group B streptococcus. Therefore the antibiotic was changed to ampicillin. To investigate the cause of polyarthritis, enhanced CT of the left shoulder and both knees was performed and demonstrated fluid collection with marginal enhancement, suggesting a bacterial abscess. However, findings of arthrocentesis and synovial fluid culture were incompatible with bacterial arthritis. A subcutaneous abscess, which appeared at 5 days after admission to the hospital, was not connected to the synovial fluid, suggesting reactive arthritis was the main cause of her polyarthritis. We performed drainage surgery and one week later, the clinical symptoms and inflammatory findings mostly disappeared. Several microbes are able to cause reactive arthritis, however, cases with Group B streptococcus are very rare. Group B streptococcus infection should be taken into consideration not only in patients with diabetes and cerebrovascular disease but also in elderly patients.