RÉSUMÉ
BACKGROUND: Only three other cases of rat bite fever caused by Streptobacillus notomytis in humans have been reported since this species was identified in 2015. Data specific to the differences in clinical features and geographic distribution between S. notomytis infection and S. moniliformis infection are scarce. All previous cases of human S. notomytis infection were reported from Japan. This is the first case of S. notomytis infection reported from outside of Japan. CASE PRESENTATION: A 72-year-old Thai woman was admitted to Siriraj Hospital (Bangkok, Thailand)-Thailand's largest university-based national tertiary referral center-in August 2020 with fever, myalgia, and polyarthralgia for 3 days, and gradually decreased consciousness for the past 1 day. Physical examination and laboratory investigations revealed septic arthritis of both knee joints, meningitis, and hepatitis. She was initially misdiagnosed as rheumatoid arthritis in the elderly since the initial investigations were unable to detect a causative pathogen. However, S. notomytis infection was later confirmed by polymerase chain reaction amplification of a part of the 16S rRNA gene and sequencing from synovial fluid. Her clinical course was also complicated by spondylodiscitis and epidural abscess caused by S. notomytis, which was detected from tissue biopsy. Therefore, rat bite fever in this patient manifested as meningitis, septic polyarthritis, hepatitis, and spondylodiscitis. The patient was treated with intravenous ceftriaxone then switched to oral amoxicillin with complete recovery. CONCLUSIONS: The clinical manifestations of S. notomytis infection are similar to those demonstrated in S. moniliformis infection. This case also showed that arthritis caused by S. notomytis mimics rheumatoid arthritis, and that meningitis and spondylodiscitis are potential coexisting complications that can be found in S. notomytis infection.