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Charlotte E. Joslin, Elmer Y. Tu; Contemporary Annualized Incidence Rates Of Acanthamoeba Keratitis. Invest. Ophthalmol. Vis. Sci. 2011;52(14):1479.
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© ARVO (1962-2015); The Authors (2016-present)
The outbreak of Acanthamoeba keratitis (AK) has persisted in Chicago and elsewhere, despite the worldwide recall in 2007 of a contact lens solution strongly associated with disease in two studies. Historical estimates suggested an annualized AK incidence rate (IR) of 1 - 2 cases per million contact lens (CL) users in the US, and 17 - 21 cases per million CL users in the UK. Here, we examine contemporary IRs given the outbreak persistence.
Area-wide referral patterns resulted in nearly if not complete capture of all Chicago area AK cases between 6/2003 - 6/2009 at University of Illinois (UIC) due to advanced diagnostic capabilities as well as clinical and research expertise. Geographic information systems (GIS) was used along with geocoded case residence and Census 2000 population data by county to estimate annualized IRs under a constant assumption of 10% market penetrance of CL use. Results were compared to historical Chicago estimates.
Annualized IRs increased from 10.2 cases in the first year of the outbreak to 30.6 per million CL users at the time of solution recall, and have continued in excess of 15 cases per million CL users subsequently with some variation by year; IRs averaged 18.9 cases per million CL users since outbreak initiation. Persistently elevated IRs are not statistically significantly lower after the solution recall than during the height of the outbreak, but are significantly higher than estimated IRs in Chicago prior to the outbreak, which are consistent with historical US IR estimates.
Annualized IRs that are considerably higher than previous US estimates 1) have continued despite the solution recall; and, 2) approximate elevated IRs in the UK during the late 1990’s, in which water cistern storage practices were believed contributory. While analyses are restricted to Chicago, results demonstrating considerably higher IRs than previous estimates likely have contemporary applicability elsewhere given the continued outbreak nationally with regional variation.
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