Microbial keratitis pathogens and antibiotic susceptibilities: A 5-year review of cases at an urban county hospital in north Texas

PURPOSE. To review the epidemiology, risk factors, microbiologic spectrum, and outcomes of microbial keratitis and to compare cases in which a causative organism is identified to those determined to be sterile during a 5-year period at a large county hospital in north Texas. METHODS. A retrospective chart review of cases of microbial keratitis at Parkland Memorial Hospital between January 2000 and December 2004. RESULTS. During this 5-year period, 132 eyes of 131 patients underwent 139 corneal scrapings for presumed microbial keratitis and an organism was reported in 73 (52.5%) cultures. Including abnormal confocal microscopy results, a causative organism was determined in 78 (56.1%) cases. At least one risk factor was present in 115 (87.1%) cases, with the most common risk factors being preexisting ocular disease, contact lens wear, and a history of trauma. Nearly 5% of patients reported a history of cocaine use. Gram staining correctly identified the organism in 20 (28.6%) culture-positive cases, and Pseudomonas aeruginosa was the most common isolate, followed by Staphylococcus aureus. The rate of S. aureus resistance to fluoroquinolones (15.4%) was similar to rates previously reported from the early to mid 1990s, but less than those reported from the late 1990s. Severe complications were more common in the nonsterile subgroup (34.2%) than in the sterile (16.9%) subgroup (P=0.041). Although the rate of acute intervention was higher in the nonsterile subgroup (27.4%) than in the sterile subgroup (20.3%), this difference was not statistically significant (P=0.461). Mean logMAR visual acuity was 1.451 (Snellen equivalent, 20/563) at presentation and 1.062 (20/231) at the last follow-up visit (P<0.001). Presenting and final visual acuities were significantly better in the sterile subgroup than in the nonsterile subgroup (P<0.001 and P=0.002, respectively). CONCLUSIONS. When a causative organism is not identified in microbial keratitis, visual acuity is not as severely affected, and fewer severe complications occur. Antibiotic resistance to fluoroquinolones and aminoglycosides, though not common, still deserves consideration in the treatment of microbial keratitis.