Risk factors for acanthamoeba keratitis in contact lens users: a case-control study

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Abstract
Objective: To investigate reasons for an increase in cases of Acanthamoeba keratitis related to contact lenses. Design: Case-control study. Cases were contact lens related acanthamoeba keratitis patients treated between 1 September 1989 and 31 August 1992. Controls were lens users without lens related disease who presented as new patients to the casualty department from 1 March 1992 to 31 August 1992. All subjects completed a questionnaire detailing lens use and hygiene practices. Setting: Eye hospital. Subjects: 35 cases with acanthamoeba keratitis and 378 controls. Main outcome measures: Relative risks comparing different contact lens types, socioeconomic classification, age, sex, lens use, lens wearing experience, hygiene compliance, and hygiene systems. Results: The crude relative risk for developing acanthamoeba keratitis with the use of daily wear disposable lenses was 49.45 (95% confidence interval 6.53 to 2227; PConclusions: Both failure to disinfect daily wear soft contact lenses and the use of chlorine release lens disinfection systems, which have little protective effect against the organism, are major risk factors for acanthamoeba keratitis. These risks have been particularly common in disposable lens use. Over 80% of acanthamoeba keratitis could be avoided by the use of lens disinfection systems that are effective against the organism. Key messages These risk factors are both more common in users of disposable daily wear soft lenses Over 80% of acanthamoeba infections could be eliminated by daily disinfection of reused lenses with systems effective against the organism Disinfection systems ineffective against acanthamoeba should not be licenced for use