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

## TL;DR

This study examines the characteristics of bacteremia in patients receiving anti-IL6 inhibitors, finding that over 40% of cases are complicated, especially in community-onset infections.

## Contribution

The study provides new insights into the clinical and microbiological features of bacteremia in patients treated with anti-IL6 inhibitors.

## Key findings

- Over 40% of bacteremia episodes in anti-IL6 recipients were complicated.
- CRP levels were lower in episodes occurring within 14 days of anti-IL6 administration.
- Common pathogens included Pseudomonas aeruginosa and Staphylococcus epidermidis.

## Abstract

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

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

Boxplots and jitter plots of the CRP levels at the blood culture sampling according to the days after anti-IL6 administration

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.

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%.

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.

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