AN EPIDEMIC OF PRESUMED ACANTHAMOEBA-KERATITIS THAT FOLLOWED REGIONALFLOODING RESULTS OF - A CASE-CONTROL INVESTIGATION

Objectives: To investigate an outbreak of presumed Acanthamoeba kerati tis (AK), to identify risk factors associated with its development, an d to characterize the changing epidemiology of AK. Methods: We perform ed a pairwise-matched case-control study involving 31 patients who wer e diagnosed as having AK between July 1993 and December 1994. Risk fac tors were identified using conditional logistic regression analysis. T o investigate the impact of regional flooding, we stratified counties within Iowa by whether their water facilities were affected and then c alculated 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 conf ocal microscopy examination results, and confirmatory cytopathologic f indings. There were no positive culture specimens. On average, cases h ad 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 p redictors of the development of AK. The presence of a humidifier in th e 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 b y the Department of Natural Resources, Des Moines, Iowa. The incidence of AK in these counties was more than 10 times higher than that in th e unaffected counties (relative risk = 10.83, 95% confidence interval, 1.48-79.49; P < .003). Conclusions: We describe an epidemic of kerati tis that, based on clinicopathologic and epidemiological evidence, is consistent with AK. As in previous outbreaks of culture-proven AK, con tact lens use was the major risk factor. Both the results of the case- control study and the population-based incidence estimates suggest tha t the recent outbreak may be caused, in part, by the effects of region al flooding. However, because the outbreak also coincided with a chang e in diagnostic techniques, we cannot eliminate recognition bias as th e reason for the apparently changing epidemiology.