Acanthamoeba Keratitis among Rigid Gas Permeable Contact Lens Wearers, United States, 2005–2011

Objective— To describe the clinical presentation and outcomes of Acanthamoeba keratitis (AK) in rigid gas permeable (RGP) contact lens wearers and identify modifiable risk factors. Design— A case-control investigation. Participants— Case-patients were RGP contact lens-wearing U.S. residents with a diagnosis of AK during 2005–2011. Controls were RGP contact lens wearers with no history of AK and at least 12 years of age. Methods— Case-patients were identified during two multi-state AK outbreak investigations. Controls from the first investigation in 2007 were identified using a reverse address directory. In the second investigation, controls were recruited from participating ophthalmology and optometry practices. Case-patients and controls were interviewed by phone using a standardized questionnaire. Odds ratios (ORs) and Fisher’s exact P-values were calculated to assess risk factors associated with infection. Main Outcome Measures— AK, a rare eye disease primarily affecting contact lens wearers, is caused by free-living amebae, Acanthamoeba spp. Results— We identified 37 case-patients in the two investigations, 10 (27%) from the 2007 investigation and 27 (73%) from 2011. There were 17 healthy controls, 9 (53%) from 2007 and 8 (47%) from 2011. Among case-patients, 9 (24%) wore RGP lenses for orthokeratology or therapeutic indication; no controls wore RGP lenses for these indications. Significant risk factors for AK were wearing lenses for orthokeratology (OR undefined, P=0.02), sleeping while wearing lenses (OR 8.00, P=0.04),