Clinical and Microbiological Outcomes of Topical 2% Acetic Acid as an Adjunct to Standardized Treatment for Pseudomonas aeruginosa-Associated Secondary Cutaneous Disease in Horses with Chronic Progressive Lymphedema: A Retrospective Historical-Control Cohort Study

Background: Chronic progressive lymphedema (CPL) in draft horses is frequently complicated by secondary cutaneous infection, and Pseudomonas aeruginosa may be difficult to eliminate. This study evaluated topical 2% acetic acid as an adjunct to a standardized local treatment protocol. Methods: Records of 35 hospitalized horses with CPL in which P. aeruginosa was the sole pretreatment isolate were reviewed retrospectively. Seven historical controls received clipping, chlorhexidine cleansing, drying, and polyhexanide irrigation; 28 horses received the same protocol plus 2% acetic acid twice daily. No horse received systemic antimicrobials. Follow-up cultures were collected 24 h after clinical resolution. Results: Median treatment duration was 12 days (IQR 11–14) in controls and 8 days (IQR 7–9) with acetic acid (p < 0.001). P. aeruginosa clearance was achieved in 1/7 (14.3%) and 27/28 (96.4%) horses, respectively (p < 0.001). Subsequent clinical reappearance of P. aeruginosa-associated disease occurred in 6/7 (85.7%) and 3/28 (10.7%) horses (p < 0.001); most control events reflected persistence rather than recurrence after clearance. No local adverse reactions were recorded. Conclusions: Adding topical 2% acetic acid was associated with higher P. aeruginosa clearance, shorter treatment, and fewer subsequent clinical reappearances. Prospective randomized studies are needed to confirm these findings.