P-65. Clinical and microbiological characteristics of bacteremia in anti-interleukin-6 inhibitor recipients

Abstract Background Interleukin (IL)-6 plays a key role in the acute-phase response to infections. Use of anti-IL-6 inhibitors (anti-IL6) is associated with serious infections, but the characteristics of bacteremia in anti-IL6 recipients remain unclear. Figure 1. Flowchart of patients’ inclusion and exclusion Figure 2. Boxplots and jitter plots of the CRP levels at the blood culture sampling according to the days after anti-IL6 administration Methods We conducted a retrospective study in the Kyoto University Hospital, including all patients developing bacteremia within 90 days of anti-IL6 administration between 2005 and 2024. “Complicated bacteremia” was defined as meeting any of the following: (1) infective endocarditis; (2) multiple foci; (3) localized suppurative complications requiring surgical intervention; (4) bone and joint infections; or (5) persistent bacteremia. Results A total of 31 episodes in 28 patients were included (Figure 1). Median age was 64 years; and 14 cases (50%) were male. Tocilizumab was given in 25 cases and sarilumab in 3 cases; indications were rheumatic diseases (15 cases), cytokine-releasing syndrome (7), Castleman’s disease (4) and COVID-19 (2). Additional immunosuppressive therapies were used in 89% of cases. In the 31 episodes, median time from last anti-IL6 administration to blood culture (BC) sampling was 19 days. Predominant foci were catheter-related bloodstream infections (n = 9) and intra-abdominal infections (9), followed by bone and joint infections (4). Sixteen episodes were caused by Gram-positives, thirteen by Gram-negatives, and two were mixed. Predominant pathogens were Pseudomonas aeruginosa and Staphylococcus epidermidis (5 episodes each), followed by S. aureus and Escherichia coli (4 episodes each). Eighteen episodes (58%) were nosocomial onset. Complicated bacteremia accounted for 13 episodes (42%), notably in 62% (8 of 13) of community-onset episodes and S. aureus bacteremia (3 of 4). C-reactive protein (CRP) levels at BC sampling were lower in episodes developing within 14 days of anti-IL6 compared to those after 15 days (23.5 mg/L vs 49.6 mg/L, p = 0.059; Figure 2). Antibiotic therapy over 14 days was administered in 20 episodes (65%). 30-day mortality was 11%. Conclusion Over 40% of bacteremia episodes in anti-IL6 recipients were complicated, especially among community-onset cases. CRP levels were lower in episodes developing within 14 days of anti-IL6 administration. Disclosures Yasufumi Matsumara, MD, PhD, Beckman Coulter: Research support for a collaborative project|Precision System Science: Research support for a collaborative project Miki Nagao, MD, PhD, Beckman Coulter: Research support for a collaborative project|Precision System Science: Research support for a collaborative project