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An Epidemic of Presumed Acanthamoeba Keratitis That Followed Regional Flooding
Results of a Case-Control Investigation
Patricia A. Meier, MD, MSc;
William D. Mathers, MD;
John E. Sutphin, MD;
Robert Folberg, MD;
Taekyu Hwang, MSc;
Richard P. Wenzel, MD, MSc
Arch Ophthalmol. 1998;116:1090-1094.
Objectives To investigate an outbreak of presumed Acanthamoeba keratitis (AK), to identify risk factors associated with its development, and to characterize the changing epidemiology of AK.
Methods We performed a pairwise-matched case-control study involving 31 patients who were diagnosed as having AK between July 1993 and December 1994. Risk factors were identified using conditional logistic regression analysis. To investigate the impact of regional flooding, we stratified counties within Iowa by whether their water facilities were affected and then calculated population-based estimates of the incidence of AK.
Results During the study, 43 presumed incident cases of AK were diagnosed; 31 were included in the case-control study. Cases were diagnosed based on the clinical presentation of keratitis, positive tandem scanning confocal microscopy examination results, and confirmatory cytopathologic findings. There were no positive culture specimens. On average, cases had symptoms for 8 weeks before diagnosis, most notably photophobia (94%), red eyes (94%), and pain (80%). Contact lens use (odds ratio [OR]=44.16; P=.02) and fishing (OR=22.62; P =.04) were independent predictors of the development of AK. The presence of a humidifier in the home (OR=0.08; P=.03) and having household water that originated from a private well instead of the municipal water supply (OR=0.12; P=.08) were protective. Twenty-nine of 30 cases resided in counties in which the water supplies were affected by flooding as determined by the Department of Natural Resources, Des Moines, Iowa. The incidence of AK in these counties was more than 10 times higher than that in the unaffected counties (relative risk=10.83, 95% confidence interval, 1.48-79.49; P <.003).
Conclusions We describe an epidemic of keratitis that, based on clinicopathologic and epidemiological evidence, is consistent with AK. As in previous outbreaks of culture-proven AK, contact lens use was the major risk factor. Both the results of the case-control study and the population-based incidence estimates suggest that the recent outbreak may be caused, in part, by the effects of regional flooding. However, because the outbreak also coincided with a change in diagnostic techniques, we cannot eliminate recognition bias as the reason for the apparently changing epidemiology.
From the Departments of Internal Medicine (Drs Meier and Wenzel), Ophthalmology (Drs Mathers and Sutphin), and Pathology (Dr Folberg), University of Iowa College of Medicine, and the University of Iowa Hospitals and Clinics, Iowa City; and the Department of Preventive Medicine and Environmental Health, University of Iowa Graduate School (Drs Meier and Wenzel and Mr Hwang). Dr Meier is now with Wilford Hall Medical Center, San Antonio, Tex, and Dr Wenzel is now with the Department of Internal Medicine, Medical College of Virginia, Virginia Commonwealth University, Richmond.
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