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


METHODS
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.
Joslin
Charlotte E
CE
Department of Ophthalmology and Visual Sciences, University of Illinois at Chicago, Chicago, Illinois 60612, USA. charjosl@uic.edu
Tu
Elmer Y
EY
McMahon
Timothy T
TT
Passaro
Doug J
DJ
Stayner
Leslie T
LT
Sugar
Joel
J
D015823:Acanthamoeba Keratitis / Q000175:diagnosis / Q000453:epidemiology*; D000293:Adolescent; D000328:Adult; D017677:Age Distribution; D000368:Aged; D002641:Chicago / Q000453:epidemiology; D015331:Cohort Studies; D003261:Contact Lenses / Q000706:statistics & numerical data; D004196:Disease Outbreaks / Q000706:statistics & numerical data*; D005260:Female; D006801:Humans; D015994:Incidence; D008297:Male; D018613:Microscopy, Confocal; D008875:Middle Aged; D015995:Prevalence; D012189:Retrospective Studies; D012307:Risk Factors; D017678:Sex Distribution