L L R R L L R R Saline Saline Solution Solution Health Effects Support Document for Acanthamoeba
Health Effects Support Document for Acanthamoeba
May 26, 2022
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Health Effects Support Document for Acanthamoeba, May 2003.U.S. Environmental Protection Agency Office of Water (4304T)
Health and Ecological Criteria Division Washington, DC 20460
www.epa.gov/safewater/ccl/pdf/acanthamoeba.pdf
i
FOREWORD
The Safe Drinking Water Act (SDWA), as amended in 1996, requires the Administrator of the Environmental Protection Agency to establish a list of contaminants to aid the agency in regulatory priority setting for the drinking water program. In addition, SDWA requires EPA to make regulatory determinations for no fewer than five contaminants by August 2001. The criteria used to determine whether or not to regulate a chemical on the CCL are the following:
• The contaminant may have an adverse effect on the health of persons.
• The contaminant is known to occur, or there is a substantial likelihood that the contaminant will occur, in public water systems with a frequency and at levels of public health concern.
• In the sole judgment of the administrator, regulation of such contaminant presents a meaningful opportunity for health risk reduction for persons served by public water systems.
The Agency’s findings for all three criteria are used in making a determination to regulate a contaminant. The Agency may determine that there is no need for regulation when a contaminant fails to meet one of the criteria. The decision not to regulate is considered a final agency action and is subject to judicial review.
This document provides the health effects basis for the regulatory determination for Acanthamoeba.
Health Effects Support Document for Acanthamoeba
ii
ACKNOWLEDGMENTS
The Health Effects Support Document for Acanthamoeba, EPA-822-R-03-012, was written by:
Nena Nwachuku, Ph.D., Office of Science and Technology, Office of Water, and Charles P. Gerba, Ph.D., University of Arizona, Tucson, Arizona. The Lead U.S. EPA Scientist on Acanthamoeba is Nena Nwachuku, Ph.D., Health and Ecological Criteria Division, Office of Science and Technology, Office of Water.
Peer review comments on two earlier versions of this document were provided by the following internal EPA peer reviewers:
Rita Schoeny, Ph.D. (Office of Science and Technology, Office of Water); Paul S. Berger, Ph.D.; Guy Carruthers; David Soderberg; James Sinclair, Ph.D. (Office of Ground Water and Drinking Water, Office of Water); and Al Dufour, Ph.D. (Office of Research and Development).
This final version also addresses comments by six external expert reviewers:
Govinda Visvesvara, Ph.D., and Hercules Moura, Ph.D., Centers For Disease Control and Prevention; A. Julio Martinez, M.D., University of Pittsburgh; Walter Jakubowski, WaltJay Consulting; Hassan Alizadeh, Ph.D., University of Texas Medical Center; and Jerry Niederkorn, Ph.D., University of Texas Medical Center.
Management support was provided by Geoffrey Grubbs, Director, Office of Science and Technology, Office of Water, U.S. EPA.
Health Effects Support Document for Acanthamoeba
iii
2.0 INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1
3.0 GENERAL INFORMATION AND PROPERTIES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1 3.1 History and Taxonomy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1 3.2 General Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2 3.3 Methods of Identification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-5 3.4 Cultivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-5 3.5 Significance of Endosymbiosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-5
4.0 OCCURRENCE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-1 4.1 Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2
4.1.1 Surface Waters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2 4.1.1.1 Freshwaters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2 4.1.1.2 Seawater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2
4.1.2 Tapwater and Bottled Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-3 4.1.3 Swimming Pools and Spas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-4 4.1.4 Sewage and Biosolids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-4
4.2 Animal Wastes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-5 4.3 Air, Dust and Soil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-5 4.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-5
5.0 HEALTH EFFECTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1 5.1 Eye Infections (Acanthamoebic Keratitis) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-3
5.1.1 Symptoms of Acanthamoeba Keratitis . . . . . . . . . . . . . . . . . . . . . . . . . 5-5 5.1.2 Diagnosis of Acanthamoeba Keratitis . . . . . . . . . . . . . . . . . . . . . . . . . . 5-6 5.1.3 Identification Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-6 5.1.4 Treatment of Acanthamoebic Keratitis . . . . . . . . . . . . . . . . . . . . . . . . . 5-6 5.1.5 Incidence of Acanthamoeba Keratitis . . . . . . . . . . . . . . . . . . . . . . . . . . 5-7 5.1.6 Pathogenicity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-8 5.1.7 Immunity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-9
Health Effects Support Document for Acanthamoeba
iv
5.2 Granulomatous Amoebic Encephalitis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-10 5.2.1 Diagnosis and Treatment of GAE . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-12 5.2.2 Incidence of GAE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-12 5.2.3 Pathogenesis and Immunity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-13
5.3 GAE in Domestic Animals and Wildlife . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-13 5.4 Other Infections caused by Acanthamoeba . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-13 5.5 Immunocompromised Individuals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-14 5.6 Incidence to Children . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-14
5.7 Effect of Endosymbiosis on Virulence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-15 6.0 HEALTH EFFECTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1
6.1 The Organism and its Occurrence (Exposure) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1 6.2 Epidemiological Evidence for Acanthamoeba Keratitis Transmission by Tapwater 6-1 6.3 Resistance to Drinking Water Treatment and Disinfection . . . . . . . . . . . . . . . . . . . 6-2 6.4 Dose Response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-3 6.5 Risk Characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-3
7.0 ASSOCIATION OF CONTACT LENSES WITH ACANTHAMOEBIC KERATITIS . . . 7-1 7.1 Types of Contact Lenses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1 7.2 Demographics of Contact Lens Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-2 7.3 Risk Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-3 7.4 Contact Lens Disinfection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-5
7.4.1 Studies of Lens Disinfection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-5 7.4.2 Hydrogen Peroxide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-6 7.4.3 Multi-Purpose Solutions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-7
8.0 DATA GAPS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-1
v
Table 3.1 Currently Identified Species of Acanthamoeba . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1
Table 3.2 Acanthamoeba Species Classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2
Table 3.3 Bacterial Endosymbionts of Acanthamoeba . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-6
Table 4.1 Occurrence of Acanthamoeba . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-1
Table 5.1 Comparison of Clinical and Pathological Features of Granulomatous Amoebic Encephalitis (GAE) and Acanthamoeba Keratitis (AK) . . . . . . . . . . . . . . . . . . . 5-1
Table 5.2 Characteristics and Symptoms of Patients with Acanthamoeba Keratitis . . . . . . 5-3
Table 5.3 Worldwide Incidence of Acanthamoeba Keratitis . . . . . . . . . . . . . . . . . . . . . . . . 5-8
Table 6.1 Human Infection Caused by Species of Acanthamoeba . . . . . . . . . . . . . . . . . . . 6-2
Table 6.2 Mechanisms involved in Acanthamoeba Keratitis . . . . . . . . . . . . . . . . . . . . . . . 6-4
Table 7.1 History of Contact Lens Development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1
Table 7.2 Types of Contact Lenses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-2
Table 7.3 Wearers and Types of Contact Lenses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-3
Table 7.4 Age Distribution of Contact Lens Wearers in the United States . . . . . . . . . . . . . 7-3
Table 7.5 Risk Factors Associated with Acanthamoebic Keratitis . . . . . . . . . . . . . . . . . . . 7-4
Table 7.6 Types of Contact Lenses Associated with Acanthamoebic Keratitis . . . . . . . . . . 7-4
Table 7.7 Risk Factors for Acanthamoebic Keratitis in Contact Lens Wearers . . . . . . . . . 7-5
Health Effects Support Document for Acanthamoeba
vi
Figure 3.2 Acanthamoeba trophozoite. .…
Health and Ecological Criteria Division Washington, DC 20460
www.epa.gov/safewater/ccl/pdf/acanthamoeba.pdf
i
FOREWORD
The Safe Drinking Water Act (SDWA), as amended in 1996, requires the Administrator of the Environmental Protection Agency to establish a list of contaminants to aid the agency in regulatory priority setting for the drinking water program. In addition, SDWA requires EPA to make regulatory determinations for no fewer than five contaminants by August 2001. The criteria used to determine whether or not to regulate a chemical on the CCL are the following:
• The contaminant may have an adverse effect on the health of persons.
• The contaminant is known to occur, or there is a substantial likelihood that the contaminant will occur, in public water systems with a frequency and at levels of public health concern.
• In the sole judgment of the administrator, regulation of such contaminant presents a meaningful opportunity for health risk reduction for persons served by public water systems.
The Agency’s findings for all three criteria are used in making a determination to regulate a contaminant. The Agency may determine that there is no need for regulation when a contaminant fails to meet one of the criteria. The decision not to regulate is considered a final agency action and is subject to judicial review.
This document provides the health effects basis for the regulatory determination for Acanthamoeba.
Health Effects Support Document for Acanthamoeba
ii
ACKNOWLEDGMENTS
The Health Effects Support Document for Acanthamoeba, EPA-822-R-03-012, was written by:
Nena Nwachuku, Ph.D., Office of Science and Technology, Office of Water, and Charles P. Gerba, Ph.D., University of Arizona, Tucson, Arizona. The Lead U.S. EPA Scientist on Acanthamoeba is Nena Nwachuku, Ph.D., Health and Ecological Criteria Division, Office of Science and Technology, Office of Water.
Peer review comments on two earlier versions of this document were provided by the following internal EPA peer reviewers:
Rita Schoeny, Ph.D. (Office of Science and Technology, Office of Water); Paul S. Berger, Ph.D.; Guy Carruthers; David Soderberg; James Sinclair, Ph.D. (Office of Ground Water and Drinking Water, Office of Water); and Al Dufour, Ph.D. (Office of Research and Development).
This final version also addresses comments by six external expert reviewers:
Govinda Visvesvara, Ph.D., and Hercules Moura, Ph.D., Centers For Disease Control and Prevention; A. Julio Martinez, M.D., University of Pittsburgh; Walter Jakubowski, WaltJay Consulting; Hassan Alizadeh, Ph.D., University of Texas Medical Center; and Jerry Niederkorn, Ph.D., University of Texas Medical Center.
Management support was provided by Geoffrey Grubbs, Director, Office of Science and Technology, Office of Water, U.S. EPA.
Health Effects Support Document for Acanthamoeba
iii
2.0 INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1
3.0 GENERAL INFORMATION AND PROPERTIES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1 3.1 History and Taxonomy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1 3.2 General Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2 3.3 Methods of Identification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-5 3.4 Cultivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-5 3.5 Significance of Endosymbiosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-5
4.0 OCCURRENCE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-1 4.1 Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2
4.1.1 Surface Waters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2 4.1.1.1 Freshwaters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2 4.1.1.2 Seawater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2
4.1.2 Tapwater and Bottled Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-3 4.1.3 Swimming Pools and Spas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-4 4.1.4 Sewage and Biosolids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-4
4.2 Animal Wastes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-5 4.3 Air, Dust and Soil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-5 4.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-5
5.0 HEALTH EFFECTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1 5.1 Eye Infections (Acanthamoebic Keratitis) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-3
5.1.1 Symptoms of Acanthamoeba Keratitis . . . . . . . . . . . . . . . . . . . . . . . . . 5-5 5.1.2 Diagnosis of Acanthamoeba Keratitis . . . . . . . . . . . . . . . . . . . . . . . . . . 5-6 5.1.3 Identification Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-6 5.1.4 Treatment of Acanthamoebic Keratitis . . . . . . . . . . . . . . . . . . . . . . . . . 5-6 5.1.5 Incidence of Acanthamoeba Keratitis . . . . . . . . . . . . . . . . . . . . . . . . . . 5-7 5.1.6 Pathogenicity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-8 5.1.7 Immunity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-9
Health Effects Support Document for Acanthamoeba
iv
5.2 Granulomatous Amoebic Encephalitis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-10 5.2.1 Diagnosis and Treatment of GAE . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-12 5.2.2 Incidence of GAE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-12 5.2.3 Pathogenesis and Immunity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-13
5.3 GAE in Domestic Animals and Wildlife . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-13 5.4 Other Infections caused by Acanthamoeba . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-13 5.5 Immunocompromised Individuals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-14 5.6 Incidence to Children . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-14
5.7 Effect of Endosymbiosis on Virulence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-15 6.0 HEALTH EFFECTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1
6.1 The Organism and its Occurrence (Exposure) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1 6.2 Epidemiological Evidence for Acanthamoeba Keratitis Transmission by Tapwater 6-1 6.3 Resistance to Drinking Water Treatment and Disinfection . . . . . . . . . . . . . . . . . . . 6-2 6.4 Dose Response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-3 6.5 Risk Characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-3
7.0 ASSOCIATION OF CONTACT LENSES WITH ACANTHAMOEBIC KERATITIS . . . 7-1 7.1 Types of Contact Lenses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1 7.2 Demographics of Contact Lens Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-2 7.3 Risk Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-3 7.4 Contact Lens Disinfection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-5
7.4.1 Studies of Lens Disinfection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-5 7.4.2 Hydrogen Peroxide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-6 7.4.3 Multi-Purpose Solutions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-7
8.0 DATA GAPS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-1
v
Table 3.1 Currently Identified Species of Acanthamoeba . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1
Table 3.2 Acanthamoeba Species Classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2
Table 3.3 Bacterial Endosymbionts of Acanthamoeba . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-6
Table 4.1 Occurrence of Acanthamoeba . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-1
Table 5.1 Comparison of Clinical and Pathological Features of Granulomatous Amoebic Encephalitis (GAE) and Acanthamoeba Keratitis (AK) . . . . . . . . . . . . . . . . . . . 5-1
Table 5.2 Characteristics and Symptoms of Patients with Acanthamoeba Keratitis . . . . . . 5-3
Table 5.3 Worldwide Incidence of Acanthamoeba Keratitis . . . . . . . . . . . . . . . . . . . . . . . . 5-8
Table 6.1 Human Infection Caused by Species of Acanthamoeba . . . . . . . . . . . . . . . . . . . 6-2
Table 6.2 Mechanisms involved in Acanthamoeba Keratitis . . . . . . . . . . . . . . . . . . . . . . . 6-4
Table 7.1 History of Contact Lens Development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1
Table 7.2 Types of Contact Lenses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-2
Table 7.3 Wearers and Types of Contact Lenses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-3
Table 7.4 Age Distribution of Contact Lens Wearers in the United States . . . . . . . . . . . . . 7-3
Table 7.5 Risk Factors Associated with Acanthamoebic Keratitis . . . . . . . . . . . . . . . . . . . 7-4
Table 7.6 Types of Contact Lenses Associated with Acanthamoebic Keratitis . . . . . . . . . . 7-4
Table 7.7 Risk Factors for Acanthamoebic Keratitis in Contact Lens Wearers . . . . . . . . . 7-5
Health Effects Support Document for Acanthamoeba
vi
Figure 3.2 Acanthamoeba trophozoite. .…
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