This prospective study found that the new, single-sample ESwab (Copan Diagnostics, Inc.) corneal culturing method provided comparable results to the standard multi-sample method for diagnosing infectious keratitis.
This study is important because this simpler technology may be beneficial in centers that do not have access to the full set of traditional culture materials. However, negative cultures occurred with both methods and, due to the low number of fungal infections at the center where the study was conducted, it is not possible to comment on Eswab’s utility in diagnosing fungal infections.
In this single-center study of 81 corneal ulcers (80 patients), the authors compared ESwab for diagnostic corneal specimen collection with the traditional multi-sample approach (using blood agar, Gram stain, Sabouraud agar, thioglycolate broth and brain heart infusion broth) for diagnostic corneal specimen collection.
ESwab is a nylon-tipped swab with spray-on flocked fiber technology and already in clinical use outside of ophthalmology. After the swab, the nylon tip is placed in 1 mL of modified Amies medium where bacterial sample viability can be maintained for 48 hours.
Using ESwab, culture positivity was 79% compared to 70% for the traditional method (75% agreement rate between methods). ESwab sensitivity was 84%, specificity 67%, positive predictive value 86% and negative predictive value 64%.
The authors note that the high proportion of patients with corneal ulcers who receive empiric treatment may be in part attributable to the low cost-effectiveness and inconvenience of the multi-sample culturing approach, particularly for nontertiary care ophthalmologists, who rarely stock multiple fresh culture media in the office.
They conclude that ESwab is a more accessible, cost-effective and less cumbersome approach to corneal culturing for ophthalmologists, particularly those in the community setting who do not have access to the full set of traditional culture materials. With comparable results to the multi-sample approach and, potentially, a lower risk of contamination, it offers both the treating and consulting ophthalmologist an initial pretreated impression of the etiology of microbial keratitis.