Original article
Epidemiological Characteristics of a Chicago-area Acanthamoeba Keratitis Outbreak

https://doi.org/10.1016/j.ajo.2006.04.034Get rights and content

Purpose

To characterize Acanthamoeba keratitis (AK) cases and analyze the geographical distribution within the Chicago-Gary-Kenosha metropolitan area, Chicago, Illinois, USA.

Design

Retrospective, population-based cohort study.

Methods

All AK cases diagnosed at the University of Illinois at Chicago Cornea Service from June 1, 2003, to November 30, 2005, were included in analysis. Patients with keratitis were defined as cases through confocal microscopy, histology, and/or positive cultures. Exploratory analyses were performed to evaluate whether AK cases were unequally distributed geographically. County population data were extracted from US Census 2000 data, and rates were age-standardized to Cook County. Poisson regression analysis was used to estimate the age-standardized rate ratio (RR) between AK cases and county of residence. Current cases (June 1, 2003 to November 30, 2005) were compared with historical cases (June 1, 2000 to November 30, 2002) to determine if the current rate of AK diagnosis differed from historical rates.

Results

Forty AK cases were diagnosed between June 1, 2003 and November 30, 2005. The average (±SD) age of patients with AK was 28.0 ± 15.0 years (range, 13 to 70 years), 52.5% were men, and 95.0% wore contact lenses. Estimated RR measures demonstrated increased rates for all counties relative to Cook, and were significant for both DuPage County (RR 3.59; 95% confidence interval [95% CI] 1.44, 8.39) and Will County (RR 3.66; 95% CI 1.18 to 9.56). Current AK diagnosis rates were significantly higher than historical rates (RR 6.67; 95% CI 3.05 to 17.52).

Conclusions

AK cases are increasing in frequency. The increased rates are unevenly distributed in the study area. Further research is warranted to better understand the increase and unusual geographical distribution.

Section snippets

Methods

The UIC Institutional Review Board reviewed and approved this research. The UIC Department of Ophthalmology, located within the Illinois Medical District immediately west of downtown Chicago, serves as a major tertiary referral center for both Chicago and the Chicago-Gary-Kenosha metropolitan area, and together with its associated hospital clinics registers approximately 64,500 outpatient visits annually. A retrospective cohort study design was used to provide descriptive statistics for current

Results

Forty AK cases were diagnosed at UIC between June 1, 2003 and November 30, 2005. Patient demographic and basic clinical information is presented in Table 2. Not surprisingly, most of the patients used contact lenses, and the use of soft lenses was much more common than the use of rigid gas permeable lenses. Slightly more than half of all cases were men, and the average age was just under 30 years. Table 3 presents the cases as well as US Census 2000 population data used in calculation of

Discussion

Our data reveal a statistically and clinically significant increase in the number of AK cases in recent years. Not only is the rate of AK diagnosis increased, but the age-standardized risk of AK is not consistent across different geographical locations in the Chicago area. As in other reported outbreaks of AK, this Chicago-area outbreak is similar in that nearly all AK cases used contact lenses.

Retrospective cohort studies are subject to certain potential biases, most importantly, the issue of

Charlotte E. Joslin, OD, is currently an Assistant Professor at the University of Illinois at Chicago, Department of Ophthalmology and Visual Sciences. Dr Joslin received her undergraduate degree from Illinois Wesleyan University and professional degree from The Ohio State University, and completed her residency training at the VA Chicago Healthcare, West Side and Hines Divisions. Dr Joslin is currently a NEI K23 awardee and is pursuing her PhD in epidemiology at the University of Illinois at

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    Charlotte E. Joslin, OD, is currently an Assistant Professor at the University of Illinois at Chicago, Department of Ophthalmology and Visual Sciences. Dr Joslin received her undergraduate degree from Illinois Wesleyan University and professional degree from The Ohio State University, and completed her residency training at the VA Chicago Healthcare, West Side and Hines Divisions. Dr Joslin is currently a NEI K23 awardee and is pursuing her PhD in epidemiology at the University of Illinois at Chicago School of Public Health.

    Elmer Y. Tu, MD, is currently an Associate Professor of Clinical Ophthalmology at the University of Illinois at Chicago serving as director of the Cornea and Refractive Surgery Service. Dr Tu completed his residency at the University of Wisconsin-Madison and cornea fellowship at the Bascom Palmer Eye Institute in Miami, Florida. Dr Tu was previously director of the Cornea and External Disease Service and Residency Program Director at the University of Texas Health Science Center, San Antonio, Texas.

    Supported in part by NIH/NEI EY 15689-01 (C.E.J.), University of Illinois at Chicago Campus Research Board (C.E.J.) Chicago, Illinois, NIH/NEI EY01792 (U.I.C.), Research to Prevent Blindness (U.I.C.), New York, New York, and the Karl Cless Foundation (U.I.C.), Northbrook, Illinois.

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