Epidemiology of bacterial corneal ulcers at tertiary centres in Vancouver, B.C

Abstract

Objective: To report the epidemiology of culture-positive bacterial corneal ulcers in Vancouver, B.C., Canada.

Design: Retrospective, observational case series.

Methods: Predetermined search terms were entered into the hospitals' electronic microbiology databases to create a cohort of patients who had undergone corneal scrapings for ulcers from April 2006 to March 2011. All specimens were plated on culture media. Cultured species were identified, and antimicrobial sensitivities were obtained. Clinical charts were then reviewed to identify associated risk factors.

Results: In total 281 corneal scrapings were included, with a positive culture recovery rate of 75%. Bacterial keratitis accounted for 84.8% of culture-positive ulcers, followed by fungi (10%) and finally Acanthamoeba (5.2%); 73% of ulcers were monomicrobial in origin and 28% polymicrobial. We found an increase in Gram-negative micro-organisms over time. General sensitivity to antibiotics did not change over time. A major risk factor for Gram-positive involvement was ocular surface disease, whereas contact lens wear was a major risk factor for Gram-negative involvement.

Conclusions: Bacterial keratitis was found to be the major cause of infectious keratitis in Vancouver, B.C. The majority of bacterial ulcers were caused by Gram-positive bacteria. However, we found an increase in Gram-negative involvement over time. Contact lens wear was identified as the major risk factor for development of Gram-negative ulcers. Pre-existing ocular disease was associated with Gram-positive infection. Susceptibility of Gram-negative bacteria to common broad-spectrum antibiotics was high, but susceptibility of Gram-positive bacteria to these antibiotics was lower and more variable.