The association between Acanthamoeba keratitis and domestic water exposure in the Chicago area

An outbreak of Acanthamoeba keratitis (AK), a rare corneal infection with significant morbidity caused by an amoebic waterborne organism, has persisted despite the recall of a contact lens solution strongly associated with disease. Environmental Protection Agency regulations reducing the allowable amount of disinfection byproducts in the water supply were implemented around the same time the AK outbreak began nationally, and an unintended consequence may be a shift in the microbial risk balance of the water supply. The relationship between AK and the domestic water supply was evaluated in Chicago to understand whether it may be contributing to the outbreak.;A case-control study was conducted including 65 cases and 175 controls recruited from the Cornea Service at the Department of Ophthalmology, University of Illinois at Chicago. Subjects completed surveys targeting contact lens hygiene and solution use as well as recreational and household water exposures, and also collected water samples from their homes that were analyzed using microbiologic techniques for the presence or absence of Acanthamoeba . Logistic regression was used to estimate the odds ratio between AK and potential risk factors. In addition, geographic information systems (GIS) was used for spatial-temporal analysis of AK cases and study controls to determine if disease patterns were consistent with possible disease transmission through the water distribution system.;Results demonstrated a statistically significant association between AK and several hygiene variables when controlling for use of the recalled solution, including solution reuse, failing to rub lenses and showering with contact lenses. Results also demonstrated a significant association between AK and positive Acanthamoeba water samples among subjects who shower with contact lenses at least once per month, and among subjects who reported never reusing contact lens solutions. Results from GIS analysis demonstrated statistically significant spatial clustering of disease. Cases were significantly further from water treatment than controls, and the location of positive Acanthamoeba water samples was significantly further from water treatment than negative Acanthamoeba water samples. In conclusion, results identified several important hygiene factors that can reduce risk, and support the hypothesis that the domestic water supply is contributing to the persisting outbreak of AK in Chicago.