Ocular Microbiology and Immunology Group
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POSTER PRESENTATION

Diagnostic Yield of Direct vs. Indirect Corneal Cultures in Infectious Keratitis

Kyle S. Chan, Kevin X. Zhang, Robin K. Kuriakose, Robert S. Feder

Department of Ophthalmology, Northwestern University Feinberg School of Medicine, Chicago, Illinois

Purpose: Infectious keratitis is a common cause of vision loss. The gold standard culturing technique for infectious keratitis involves direct inoculation of corneal scrapings onto growth media (direct culture). An alternative technique involves inoculation of a swab in liquid transport media (indirect culture). We investigated whether there is a change in diagnostic yield with direct vs. indirect corneal cultures.

Methods: This is a retrospective review of patients seen for infectious keratitis and evaluated with corneal culture at Northwestern Memorial Hospital between 2013 to 2023. Sociodemographic and clinical variables, including age, sex, contact lens wear, exam findings, culture results, and antibiotic treatment, were collected. Statistical analysis was performed comparing culture positivity based on method of culture and other variables of interest.

Results: The cohort consisted of 141 corneal cultures from 115 patients, with 77 (54.6%) cultures being direct and 64 (45.4%) being indirect. Culture method was not associated with culture positivity or growth of common pathogenic organisms. Contact lens wear was associated with increased Pseudomonas aeruginosa growth (P = 0.032). LogMAR ≥ 0.6 was associated with culture positivity (P=0.033) in cases of direct culture, while prior antibiotic use was associated with culture negative results (P < 0.01) in cases of indirect culture.

Conclusions: There was no significant difference in diagnostic yield and growth of common pathogenic organisms between direct and indirect corneal culture at our institution. Given the cost effectiveness, convenience, and efficacy of the indirect culture method, it should be adopted as the primary culture technique used in the evaluation of infectious keratitis.