Risk factors for treatment outcome of suspected microbial keratitis

Background-Primary treatment for suspected microbial keratitis is generally successful. Although risks such as contact lens use are well recognised as causative factors for microbial keratitis, little is known about the risk factors that influence treatment outcome. The present study evaluates the r isk factors assessed at diagnosis as prognostic indicators of primary treat ment failure. Methods-Patients were prospectively enrolled in the ofloxacin treatment tri al and data concerning symptoms, treatments, past and concurrent eye diseas e were collected along with the measurement of corneal ulcer size at the sl it lamp. All patients were scraped for microbiological investigation, and t reated with either ofloxacin (0.3%) or standard therapy of fortified cefuro xime and gentamicin drops. Treatment success was complete healing of the ul cer with zero dimensions of the epithelial defect within 2 weeks of start o f treatment. The important prognostic indicators were selected by compariso n among those who failed treatment, had delayed healing, or were culture po sitive with other patients using univariate and stratified analysis. These were then used in a Poisson model for multiple regression analysis to estim ate the relative risk of the main prognostic variables. Results-Of the 118 patients enrolled in the study, 14 were identified as pr imary treatment failures, 17 had slow healing, and 15 indolent ulcers. Ther e were 49 culture positive patients. The multivariate analysis identified t hat large culture positive ulcers in patients 60 years or older had 5.5 tim es the risk of primary treatment failure (p<0.001). Significant predictors of slow healing were previous ocular disease and a positive culture; signif icant predictors of indolent ulceration were previous ocular disease and st eroid use at diagnosis; the main predictor of a culture positive result was ulcer size. Conclusions-Elderly patients with large ulcers were more likely to be cultu re positive, fail primary therapy, and require surgical intervention. A pos itive microbial culture provided prognostic information regardless of the o rganism isolated. However, this information was of less value for those wit h small ulcers and for younger patients.