Microbial Contamination of In-Use Ocular Medications

Abstract

Two hundred twenty in-use medications from 101 patients with non-microbial ocular surface disease were studied by sterile culture of the bottle caps, a drop produced by simple inversion, and the interior contents. Conjunctival cultures were taken from these patients and 50 aged-matched controls. Pathogenic organisms were harvested from conjunctivae significantly more frequently (p < 0.01) from cases (34%) than from controls (10%). Twenty-nine percent of medications had microorganisms cultured from at least one medication site. Gram negative organisms were significantly more likely (p < 0.00001) to be isolated from all medication sites than gram positive organisms. Forty-nine percent of the gram negatives, but none of the pathogenic gram positives (p < 0.01), isolated from the conjunctivae were also found in the drops of their associated medications. We conclude that this cycle of contamination between in-use medications and conjunctivae may represent an important risk factor for microbial keratitis in patients with ocular surface disease.