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2026 OMIG Abstract

Infectious Keratitis Isolates and Susceptibility in the Pacific Northwest

LuAnna Rochelle², Alexa Watson², Emilia Hommestaad¹, Ryan Liao¹, Leona Ding³, Andrew Chen³,
Shu Feng³, Miel Sundararajan³, and Minh Nguyen³

¹University of Washington, Seattle, Washington; ²University of Washington School of Medicine, Seattle, Washington; ³Department of Ophthalmology, University of Washington School of Medicine, Seattle, Washington

Purpose: To examine causative microorganisms and antibiotic susceptibility profiles of culture-positive infectious keratitis in the Pacific Northwest over an 11-year period.

Methods: This retrospective study reviewed medical records identified by diagnosis codes for microbial keratitis from January 1, 2014, to December 31, 2024, at the University of Washington. Cases of viral keratitis were excluded. Prevalence, antibiotic susceptibility, and yearly trends were analyzed.

Results: A total of 443 microbial isolates where identified. Of these, 380 (85.8%) were bacteria, 47 (10.6%) were fungi, and 16 (3.6%) were Acanthamoeba. The most common bacterial species was Staphylococcus (n = 96, 25%), and the most common gram-negative was Pseudomonas (n = 63, 16.5%). Among fungi, Candida was the most common (n = 15, 33%). Bacterial isolates showed a meaningful decrease in the relative proportion year after year (B = -0.015, P < 0.001, 95% CI [-0.020, -0.009]). However, both fungi and Acanthamoeba showed a significant increase in proportion each year (fungi: B = 0.009, P = 0.012, 95% CI [0.002, 0.015]; Acanthamoeba: B = 0.006, P = 0.012, 95% CI [0.002, 0.010]). Fifty-one percent (n = 37 / 72) of Staphylococcus isolates showed resistant to erythromycin.

Conclusions: Microbial keratitis in the Pacific Northwest is most commonly caused by bacteria. However, there was a meaningful increase in fungal and Acanthamoeba cases. As a result, clinicians in this region should maintain a high index of suspicion for these pathogens and pursue early diagnostic testing. Use of erythromycin for empiric treatment warrants further inspection.