#633 Pathogen distribution and clinical outcomes of aHUS patients on peritoneal dialysis

Abstract Background and Aims Atypical hemolytic uremic syndrome (aHUS) is a rare, life-threatening thrombotic microangiopathy that can lead to end-stage renal disease (ESRD). While peritoneal dialysis (PD) is an option, infection may trigger aHUS instability. Some ESRD patients require ongoing anticomplement therapy for persistent extra-renal manifestations. This study examines PD outcomes in aHUS patients, comparing those with and without regular anticomplement therapy, and analyzes pathogen differences between aHUS and non-aHUS PD patients. Method We retrospectively analyzed aHUS patients on PD at a single Taiwan center (Jan 2017–Oct 2024). Outcomes and pathogen profiles were compared between those with and without regular anticomplement therapy, and pathogen distribution was examined between aHUS and non-aHUS PD patients. Results Twelve aHUS patients on PD were included, six developing peritonitis across 24 episodes. Three remained on regular anticomplement therapy due to multiple system involvement and prior flare-ups upon dose reduction, while three did not. In those on therapy, pathogens included Staphylococcus hominis, Staphylococcus epidermidis, Staphylococcus haemolyticus, Staphylococcus capitis, Staphylococcus aureus (MRSA), and Proteus mirabilis (each in one episode). Polymicrobial infections involved Staphylococcus epidermidis + Staphylococcus haemolyticus, Streptococcus salivarius + Streptococcus mitis, Citrobacter freundii + Enterococcus faecalis, Serratia marcescens + Pseudomonas aeruginosa, Elizabethkingia anophelis, and Sphingomonas koreensis, with four culture-negative episodes. Five required PD catheter removal and hemodialysis (HD) conversion. In those without therapy, pathogens included Corynebacterium striatum, Streptococcus gallolyticus, Staphylococcus aureus, and Staphylococcus lugdunensis (each in one episode), while Staphylococcus epidermidis appeared in three episodes and Acinetobacter baumannii in one. Two were culture-negative, and one required HD conversion. No fungal infections were observed. Among 335 non-aHUS patients with 465 PD peritonitis episodes, 26 were polymicrobial (excluding secondary peritonitis). The most common pathogens were Staphylococcus aureus (59), Staphylococcus epidermidis (49), Escherichia coli (46), Staphylococcus aureus (MRSA) (32), Staphylococcus haemolyticus (27), Pseudomonas aeruginosa (22), Klebsiella pneumoniae (16), Enterococcus faecalis (15), Staphylococcus capitis (11), and Streptococcus salivarius (10). Fungal peritonitis occurred in 16 episodes, with one tuberculosis-related case. Pathogen distribution did not differ significantly among non-aHUS, aHUS, and aHUS with/without regular anticomplement therapy (Fisher's Exact Test, P ≥ 0.05; RR analysis). One patient on regular therapy had a rare Elizabethkingia anophelis and Sphingomonas koreensis infection, possibly reflecting aHUS-related immune alterations. Though not statistically significant, these pathogens were rarely seen in non-aHUS cases, suggesting clinical relevance. All three patients on regular therapy discontinued treatment during peritonitis, yet none of the six aHUS PD peritonitis patients experienced instability or exacerbation. Conclusion Peritoneal dialysis is viable for aHUS patients with ESRD, including those on anticomplement therapy. Pathogen distribution showed no significant differences across groups. Despite treatment discontinuation during peritonitis, no aHUS patients experienced disease instability. Given the rarity of aHUS, monitoring hemolytic markers remains crucial in PD peritonitis.