Impact of prior therapy on the recovery and frequency of corneal pathogens

Objective: To document the impact of prior antibiotic therapy on the recovery of corneal pathogens. Methods: Medical records and laboratory reports of 334 consecutive microbial keratitis patients examined from January to December 2000 were reviewed. Comparisons of pathogens, culture positive rate, recovery time, antibiotic sensitivity profile, delay in presentation, and final visual acuity were analyzed for patients treated before presentation and those who were not. The chi(2) test was used to determine statistical significance. Results: Of the 334 patients, 56% were exposed to at least one course of topical antimicrobials before culture. Patients on therapy were only slightly more likely to be culture negative (P = 0.317) but significantly more likely to have a delay in pathogen recovery (P = 0.002). Patients given prior antibiotics took significantly longer to heal (P = 0.003). Gram-negative organisms (47.5%) were the most frequent pathogens isolated from all culture-positive patients, followed by gram positives (28.7%), fungi (15.8%), and parasites (2%). An increase and significant difference in the frequency of fungi (P = 0.000) and acanthamoeba was reserved for the pre-treated group. Gram negative organisms were more often isolated from patients who had not been pretreated (P = 0.002). Pretreated patients were more like to have a pathogen resistant to I or more of the commonly prescribed ocular antibiotics (P = 0.02). Conclusions: There is a delay in starting microbiologic-guided antibiotic treatment in patients who have received empiric therapy. Nonbacterial corneal pathogens may be associated more frequently with patients on prior therapy.