Differentiation of etiologic agents of bacterial keratitis from presentation characteristics

Presenting characteristics of bacterial corneal ulcers may suggest particular causative organisms, helping to guide treatment decisions before cultures become available. In this study, we analyze the association between presentation demographic and clinical characteristics, using data collected as part of a randomized, controlled clinical trial. Data for this study were collected as part of the Steroids for Corneal Ulcers Trial, a randomized, placebo-controlled, double-masked trial. All patients had a culture-proven bacterial corneal ulcer. Patient history, clinical examination, and photography were performed in a standardized fashion at enrollment. Analysis of variance or Fisher's exact test was used to compare characteristics by organism. Univariate logistic regression was used to analyze predictors of the most common organisms. Five hundred patients were enrolled in the trial, of whom 488 were included in this analysis. The most common organism was Streptococcus pneumoniae (N = 248, 51 %) followed by Pseudomonas aeruginosa (N = 110, 23 %). Compared to other organisms, P. aeruginosa was significantly associated with a larger baseline infiltrate/scar size [odds ratio (OR) 1.6, 95 % confidence interval (CI) 1.4-1.8] and deeper infiltrate (OR 2.4, 95 % CI 1.5-3.8). S. pneumoniae was significantly associated with a smaller baseline infiltrate/scar size (OR 0.8, 95 % CI 0.7-0.9) and dacryocystitis (OR 7.3, 95 % CI 4.1-13.3). Nocardia spp. were significantly associated with longer duration of symptoms prior to presentation (OR 1.4, 95 % CI 1.2-1.6), more shallow infiltrate (OR 0.3, 95 % CI 0.2-0.5), and better baseline visual acuity (OR 0.4, 95 % CI 0.2-0.65). Staphylococcus spp. were less likely to be central in location (OR 0.16, 95 % CI 0.08-0.3). Baseline characteristics of bacterial ulcers may suggest the likely etiology and guide early management.