Is Corynebacterium An Emerging And Underestimated Pathogen In Infectious Keratitis? A 22-Year Epidemiological Analysis

To investigate long-term trends in Corynebacterium spp. isolated from corneal scrapings and to evaluate whether its increasing detection challenges the traditional perception of this organism as merely commensal ocular flora.

Retrospective single-center microbiological cohort study conducted at a tertiary referral hospital between January 2003 and June 2025.

All corneal scrapings positive for Corynebacterium spp. were extracted from the institutional microbiology database. Annual incidence, referral source, contamination labeling, and colony growth intensity were analyzed. Subperiod comparison (2003–2012 vs 2013–2025) and linear regression were used to assess temporal trends. Seasonal distribution was evaluated using chi-square testing.

A total of 195 positive corneal scrapings were identified over 22 years. Most cases originated from the Emergency Department (63.1%), and only 1.5% were classified as probable contamination. A significant linear increase in annual isolation was observed (β=0.37 cases/year; p=0.017). Cases from 2013–2025 accounted for 71.3% of the cohort compared with 28.7% during 2003–2012 (p<0.0001). Multi-colony growth (≥2 isolates) was present in 35% of cases. Seasonal analysis showed a non-significant predominance in autumn and spring (p=0.088), suggesting a pattern distinct from typical summer-associated keratitis pathogens.

Over the past two decades, Corynebacterium isolation in corneal scrapings has significantly increased. The sustained temporal rise, low contamination labeling rate, and substantial proportion of multi-colony growth collectively challenge the assumption that Corynebacterium represents incidental flora. These findings support reconsideration of its potential role as an emerging and underestimated pathogen in infectious keratitis.