Comparison of Rates of Positive Cultures in Patients with Bacterial Keratitis With and Without Previous Empiric Treatment Krishna Patel 1, Shuchi B. Patel MD 1, Michael A. Saidel MD 1 1 Division of Ophthalmology and Visual Science, University of Chicago, Chicago, IL Authors have no financial interests

Purpose To analyze the rates of positive cultures at our institution and to compare the rates of positive cultures from patients on no previous treatments versus those on empiric antibiotic treatment prior to obtaining a culture specimen.

Methods A retrospective chart review was done for all patients identified as having a corneal ulcer between the years 2002 and Only patients with central corneal ulcers were included in the study. Patients with viral, fungal, protozoan or neurotrophic ulcers were excluded. Whether the patient was treatment naive or had already begun treatment prior to acquisition of a culture sample was noted. The rate of positive cultures in these subgroups was then analyzed.

Cultures Technique – Taken with Kimura spatula – With or without anesthesia – Streaked on blood, chocolate, and Sabourad dextrose agar Lowenstien-Jensen, thioglycolate, nonnutrient agar with E. Coli overlay used if appropriate – Sent for Gram and Giemsa stain Considered a positive culture If at least one colony was seen on two or more media Or if a colony was present on a single medium and the organism was also identified on staining.

Results 251 charts reviewed. 62 ulcers were included in the study. – 53 of 62 ulcers were cultured (85%). – 3 of the 9 ulcers not cultured were on previous antibiotics(33%). – 19 of the 62 ulcers were on previous treatment (30%). – 16 of the 53 cultured ulcers were on previous treatment(30%). – 9 of the cultures on previous treatments were negative (56%) – 7 of the cultures on previous treatments were positive(44%).

Positive cultures on previous treatment Moxifloxacin- Grew Coagulase negative staphylococcus Ciprofloxacin- Grew Coagulase negative staphylococcus Tobramycin/dexamethasone- Grew Coagulase negative staphylococcus Erythromycin - Grew both Psuedomonas aeruginosa and Coagulase negative staphylococcus Sulfacetimide- Grew Coagulase negative staphylococcus Sulfacetimide- Grew Psuedomonas aeruginosa

Negative cultures on previous treatment Negative cultures were found with patients on the following drops – Moxifloxacin- 3/9 – Gatifloxacin- 2/9 – Moxifloxacin/Tobramycin combination- 1/9 – Gatifloxacin/Polytrim combination- 1/9 – Ciprofloxacin-1/9 – Tobramycin/dexamethason-1/9

The overall rate of positive cultures was 64% (34/53). 27/37 (73%) cultures were positive in patients not on previous antibiotics. 7/16 cultures were positive (44%) with previous empiric therapy.

Conclusion As predicted, there was a higher rate of positive cultures from samples obtained prior to the start of antibiotic treatment. Interestingly, there was still a significant positive culture rate from patients who were already on empiric therapy. This may be due to the fact that we are a tertiary care center so patients previously started on treatment may have been referred due to unresponsiveness to therapy. Yet, when compared to previously published literature from other tertiary care centers, we found that more gram positive pathogens from the cultures, while previously it has been reported that most commonly gram negative pathogens are recovered.

Also, it had been reported that pathogens recovered from cultures on empiric treatment have higher resistance rates to a spectrum of antibiotics which we also did not find in our retrospective study. Therefore, it may be useful to culture ulcers even from patients on empiric treatment to optimize antibiotic choice, especially if there is a poor response to the current antibiotic regimen.

Further studies with a larger cohort should be conducted and should include the recovery time of the pathogen from the culture specimen. This data will help establish the utility of culturing patients already on empiric antibiotic treatment.

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