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Polymicrobial Versus Monomicrobial Keratitis: A Retrospective Comparative Study

Lim, Nigel C. S.; Lim, Dawn K. A. M.R.C.P., M.Med (Int Med), M.Med (Ophthal); Ray, Manotosh M.D., F.R.C.S.

doi: 10.1097/ICL.0b013e3182a3024e

Objectives: To compare the risk factors, clinical characteristics, microbiological profile, and treatment outcomes of polymicrobial versus monomicrobial keratitis.

Methods: In this retrospective comparative case series, eyes with polymicrobial and monomicrobial keratitis were identified from microbiological records at a tertiary academic referral center, from January 2002 to December 2010. Only culture positive cases were included. Eyes with infectious keratitis involving two or more pathogens were included in the polymicrobial group, whereas eyes infected solely by Pseudomonas aeruginosa were included in the monomicrobial group. Various parameters including demographics, risk factors, clinical and microbiological characteristics, and treatment outcomes were analyzed.

Results: Twenty-one eyes each with polymicrobial and monomicrobial keratitis were included in this study. The mean age of polymicrobial patients was significantly higher than monomicrobials. Use of contact lens was the commonest predisposing factor in both groups. Systemic (23.8%) and multiple (33.3%) risk factors were involved in eyes with polymicrobial keratitis only. The mean size of corneal infiltrates and mean duration for resolvement of infection were significantly greater in the polymicrobial group. Medical treatment was successful only in 80.9% eyes with polymicrobial keratitis, whereas all monomicrobial keratitis patients responded to it. A total of 44 organisms belonging to 18 species (bacteria = 13, fungi = 5) were isolated from the polymicrobial group. P. aeruginosa and Candida albicans were the most frequently isolated bacteria (n = 12) and fungi (n = 5), respectively. In the polymicrobial group, gram-negative organisms were most sensitive to gentamicin (87.8%), followed by ciprofloxacin (78.7%), whereas gram-positive organisms were 100% sensitive to ciprofloxacin and cefazolin.

Conclusions: A high index of suspicion of polymicrobial keratitis should be made in patients with multiple and systemic risk factors. Contact lens usage was the most common risk factor in both groups. Size of corneal infiltrate is a fairly reliable indicator for suspecting polymicrobial keratitis. Prolonged course of the disease and decreased antibiotic sensitivity were the other notable features of polymicrobial keratitis.

Department of Ophthalmology (N.C.S.L., M.R.), Yong Loo Lin School of Medicine, National University of Singapore, and Department of Ophthalmology (D.K.A.L., M.R.) National University Health System, Singapore, Singapore.

Address correspondence to Manotosh Ray, M.D., F.R.C.S., Consultant, Department of Ophthalmology, National University Hospital, 1E, Kent Ridge Road, NUHS Tower Block, Level 7, Singapore 119228, Singapore; e-mail:

The authors have no funding or conflicts of interest to disclose.

Accepted June 30, 2013

© 2013 Contact Lens Association of Ophthalmologists, Inc.