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C. E. Joslin, E. Y. Tu, M. E. Shoff, G. C. Booton, P. A. Fuerst, M. S. Dworkin, R. J. Anderson, L. T. Stayner, F. G. Davis; The Association Between Acanthamoeba Keratitis and Water Samples Positive for Acanthamoeba in the Chicago Area Acanthamoeba Keratitis Case-Control Study. Invest. Ophthalmol. Vis. Sci. 2010;51(13):1309.
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Background: An outbreak of Acanthamoeba keratitis (AK), a painful infection caused by a ubiquitous waterborne protozoan, has persisted despite the recall in 2007 of a contact lens solution strongly associated with disease in 2 studies (Chicago AK Study and CDC AK Outbreak Investigation). Environmental Protection Agency regulations reducing allowable disinfection byproducts in potable water were implemented concomitant to the outbreak; a microbial shift may be an unintended consequence. The relationship between AK and potable water was evaluated to understand the contribution.
AK is difficult to treat, requiring therapy with specific, compounded, anti-acanthamoebal medication and frequently a penetrating keratoplasty; as such, we have captured nearly, if not all cases in Chicago. 84 AK cases diagnosed 6/03 - 6/09 and 202 controls matched on contact lens use, age, and date were recruited from the UIC Cornea Service. Water samples collected 7/06 - 7/09 from subjects' homes were analyzed for Acanthamoeba presence. Logistic regression was used to estimate the association between AK and positive Acanthamoeba water samples, regardless of care solution or lens hygiene as the outbreak persists. Analyses performed included: 1) restriction to subjects with soft contact lens (SCL) use; and, 2) inclusion of all subjects, matching on SCL use.
Among subjects with SCL use, positive water samples were present in 31 of 158 (19.6%) homes, and the risk of positive water samples was statistically elevated among cases (OR: 2.39; 95% CI: 1.04 - 5.49). Results were similar when analyses included all subjects (OR: 2.10; 95% CI: 1.03 - 4.29). No statistical evidence of interaction between positive water samples and use of the recalled solution existed, with a similar odds ratio magnitude and confidence interval width regardless of whether or not the recalled solution was used.
This is the first population-based study to identify that Acanthamoeba presence in the water supply significantly increases the risk of AK. Results support hypotheses that the domestic water supply is contributing to the persisting AK outbreak.
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