An epidemic of presumed Acanthamoeba keratitis that followed regional flooding

Results of a case-control investigation

Patricia A. Meier, William Mathers, John E. Sutphin, Robert Folberg, Taekyu Hwang, Richard P. Wenzel

Research output: Contribution to journalArticle

38 Citations (Scopus)

Abstract

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.

Original languageEnglish (US)
Pages (from-to)1090-1094
Number of pages5
JournalArchives of Ophthalmology
Volume116
Issue number8
StatePublished - Aug 1998
Externally publishedYes

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Acanthamoeba Keratitis
Disease Outbreaks
Odds Ratio
Case-Control Studies
Keratitis
Water Supply
Contact Lenses
Incidence
Epidemiology
Eye Pain
Photophobia
Water
Confocal Microscopy
Population
Logistic Models
Regression Analysis
Confidence Intervals

ASJC Scopus subject areas

  • Ophthalmology

Cite this

An epidemic of presumed Acanthamoeba keratitis that followed regional flooding : Results of a case-control investigation. / Meier, Patricia A.; Mathers, William; Sutphin, John E.; Folberg, Robert; Hwang, Taekyu; Wenzel, Richard P.

In: Archives of Ophthalmology, Vol. 116, No. 8, 08.1998, p. 1090-1094.

Research output: Contribution to journalArticle

Meier, Patricia A. ; Mathers, William ; Sutphin, John E. ; Folberg, Robert ; Hwang, Taekyu ; Wenzel, Richard P. / An epidemic of presumed Acanthamoeba keratitis that followed regional flooding : Results of a case-control investigation. In: Archives of Ophthalmology. 1998 ; Vol. 116, No. 8. pp. 1090-1094.
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abstract = "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.",
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T1 - An epidemic of presumed Acanthamoeba keratitis that followed regional flooding

T2 - Results of a case-control investigation

AU - Meier, Patricia A.

AU - Mathers, William

AU - Sutphin, John E.

AU - Folberg, Robert

AU - Hwang, Taekyu

AU - Wenzel, Richard P.

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