Secondary Microbial Infection in Pyoderma Gangrenosum: Comparable Rates to Venous Ulcers in a Retrospective Cohort

ABSTRACT Pyoderma gangrenosum (PG) is a neutrophilic dermatosis traditionally regarded as a sterile inflammatory ulcer; however, positive wound cultures are frequently encountered in clinical practice and may complicate or delay diagnosis and management. Data regarding bacterial superinfection in PG remain limited. The objective of this study was to determine the frequency and spectrum of microbial involvement in PG ulcers compared with venous ulcers. We performed a retrospective cohort study of patients evaluated at the University of Utah between June 2012 and June 2025. Electronic medical records were queried using International Classification of Diseases codes to identify patients with PG or venous ulcers, with diagnosis confirmed by manual chart review. Ulcers were included if at least one bacterial wound swab or tissue culture had been obtained. Isolated organisms were recorded, and associations between ulcer type and organism isolation were analysed using Fisher's exact test. The cohort included 292 patients (143 PG, 149 venous ulcers). Secondary microbial growth occurred in 50.3% of PG ulcers and 50.3% of venous ulcers. Pseudomonas aeruginosa was isolated in 11.9% of PG ulcers and 9.4% of venous ulcers ( p = 0.57). Staphylococcus species were the most frequently identified organisms in both groups. No statistically significant difference in overall culture positivity or Pseudomonas isolation was observed between ulcer types. These findings demonstrate that PG ulcers are not uniformly sterile, with approximately half demonstrating microbial superinfection. Infection rates were comparable to those observed in venous ulcers, suggesting that secondary microbial involvement is common across chronic wound types. Positive cultures should not preclude the diagnosis of PG, and recognition of superinfection may support appropriate antimicrobial use while avoiding diagnostic delay.