Septic arthritis induced by Streptococcus pneumoniae occurring in rheumatoid arthritis treated with abatacept and methotrexate: A case report

Septic arthritis occurs more frequently in elderly patients with rheumatoid arthritis (RA), with Staphylococcus aureus being the most common aetiologic agent. Rarely, Streptococcus pneumoniae (pneumococcus) is the cause of septic arthritis. Biological disease-modifying antirheumatic drugs (bDMARDs) are widely used in RA, but it is unknown whether bDMARDs could be a risk factor for pneumococcal septic arthritis in such patients. Here, we report the case of a patient with RA treated with bDMARDs (abatacept) who developed pneumococcal septic arthritis. The patient is a 64-year-old female complicated with RA for >10 years. She was treated with abatacept and methotrexate and has been in remission for 2 years. She had not received any pneumococcal vaccination. She consulted at our hospital for left ankle arthralgia and fever. Blood culture and puncture of the left ankle joints detected pneumococcus, and the pneumococcal urine antigen test was positive. The patient was diagnosed with pneumococcal septic arthritis, and she recovered after the administration of antibiotics. This is the first case report discussing these circumstances, suggesting that bDMARDs may be a risk of pneumococcal septic arthritis in patients with RA. To prevent this, pneumococcal vaccination should be encouraged in such patients. Furthermore, if RA is in remission, we may consider the spacing or withdrawal of bDMARDs to avoid severe infection.