Background: Appendicitis remains a common surgical emergency in children. Empirical antibacterial treatment is indicated to reduce infective complications. We investigate the bacterial pathogens identified intra-operatively during appendectomies in children to guide empirical surgical antimicrobial prophylaxis options.

Methods: A retrospective analysis of patients (<18 years old) undergoing an appendectomy across a multisite London hospital (Nov2019-March2022) was undertaken. Patient-related outcomes including length of hospital stay (LOS), days of antibacterial therapy (DOT), intra-operative microbiology and post-operative radiology reports were interrogated.

Results: 304 patients underwent an appendectomy during this period; 39.1% of patients had intraoperative samples cultured. Bacterial pathogens were found in 73/119 (61.3%) cases; the most common isolates being Escherichia coli (42.0%), Pseudomonas aeruginosa (21.0%), Streptococcus milleri. (14.3%) and Bacteroides fragilis (5.9%). Polymicrobial infection was common (32/73). Isolation of Pseudomonas spp. from intra-operative sampling was associated with a greater LOS (7.0 vs 5.0 days; p=0.011) but nil effect on the incidence of postoperative collections. Presence of Streptococcus milleri was associated with longer LOS (7.0 vs 5.0 day; p=0.007), DOT (12.0 vs 8.5 day; p=0.007) but had no observed outcome on postoperative collections (29.4% vs 18.6%; p=0.330). 48% of E. coli positive cultures were co-amoxiclav resistant and prolonged LOS compared to the non-resistant group (7.0 vs 5.0 days; p=0.040) but had no difference in post-operative collections (29.2% vs 17.9%; p=0.260).

Conclusion: A high proportion of children with appendicitis have Pseudomonas spp. isolated, leading to a prolonged LOS. Evolving Enterobacterales resistance and the presence of Pseudomonas spp. necessitate extended antibacterial coverage for paediatric appendectomies with evidence of peritonitis