EPA 822-R-09-002 

REVIEW OF ZOONOTIC PATHOGENS 

IN AMBIENT WATERS 

U.S. Environmental Protection Agency 

Office of Water 

Health and Ecological Criteria Division 

February 2009 
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DISCLAIMER

This document has been reviewed in accordance with U.S. Environmental Protection Agency 

policy and approved for publication. Mention of trade names or commercial products does not 

constitute endorsement or recommendation for use. 
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ACKNOWLEDGMENTS

Questions concerning this document or its application should be addressed to the EPA Work 

Assignment Manager: 

John Ravenscroft 

USEPA Headquarters 

Office of Science and Technology, Office of Water 

1200 Pennsylvania Avenue, NW 

Mail Code: 4304T 

Washington, DC 20460 

Phone: 202-566-1101 

Email: ravenscroft.john@epa.gov 

This literature review was managed under EPA Contract EP-C-07-036 to Clancy Environmental 

Consultants, Inc. The following individuals contributed to the development of the report: 

Lead writer: Audrey Ichida ICF International 

Leiran Biton ICF International 

Alexis Castrovinci ICF International 

Jennifer Clancy Clancy Environmental Consultants 

Mary Clark ICF International 

Elizabeth Dederick ICF International 

Kelly Hammerle ICF International 

Walter Jakubowski WaltJay Consulting 

Margaret McVey ICF International 

Michelle Moser ICF International 

Jeffery Rosen Clancy Environmental Consultants 

Tina Rouse ICF International 

Jennifer Welham ICF International 

Kerry Williams ICF International 
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TABLE OF CONTENTS

ACKNOWLEDGMENTS ................................................................................................................................................. iii

TABLES AND FIGURES ................................................................................................................................................. vii

ACRONYMS ................................................................................................................................................................... ix

EXECUTIVE SUMMARY ................................................................................................................................................. 1

I. BACKGROUND AND INTRODUCTION .................................................................................................................... 5

I.1 Background: Context and Purpose ............................................................................................................ 5

I.2 Introduction ................................................................................................................................................ 6

II. KEY WATERBORNE ZOONOTIC PATHOGENS OF CONCERN ............................................................................... 8

II.1 Bacteria ...................................................................................................................................................... 8

II.1.1 Escherichia coli ............................................................................................................................. 8

II.1.2 Campylobacter ............................................................................................................................ 12

II.1.3 Salmonella ................................................................................................................................... 14

II.1.4 Leptospira .................................................................................................................................... 17

II.2 Protozoa ................................................................................................................................................... 19

II.2.1 Cryptosporidium .......................................................................................................................... 19

II.2.2 Giardia ........................................................................................................................................ 26

II.3 Viruses Zoonotic Potential ....................................................................................................................... 33

III. PATHOGEN INTERACTIONS WITH THEIR ENVIRONMENT ................................................................................. 37

III.1 Water Environment Affects Pathogen Survivability and Phenotype ....................................................... 37

III.1.1 Pathogenic E. coli Survival in the Environment .......................................................................... 38

III.1.2 Campylobacter Survival in the Environment .............................................................................. 39

III.1.3 Salmonella Survival in the Environment ..................................................................................... 39

III.1.4 Leptospira Survival in the Environment ...................................................................................... 39

III.1.5 Cryptosporidium Survival in the Environment ............................................................................ 40

III.1.6 Giardia Survival in the Environment .......................................................................................... 43

III.1.7 Virus Survival in the Environment .............................................................................................. 44

III.2 Host Animals Can Influence Pathogen Characteristics and Mechanisms of Rapid Evolution ................ 44

IV. SUMMARY ........................................................................................................................................................... 49

V. REFERENCES ...................................................................................................................................................... 50

APPENDIX A: WATERBORNE PATHOGENS .............................................................................................................. A-1

APPENDIX B: LITERATURE SEARCH STRATEGY AND RESULTS ............................................................................. B-1

APPENDIX C: INCIDENTAL INGESTION OF AMBIENT WATER DURING RECREATIONAL ACTIVITIES ................... C-1
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TABLES AND FIGURES

Table II.1.1-1. Outbreaks of E. coli Associated with Recreational Waters in the United States. ........................ 12 

Table II.2.1-1. 

Table II.2.1-2. 

Table II.2.2-1. 

Table II.2.2-2. 

Table II.2.2-3. 

Cryptosporidium Species ............................................................................................................. 20 

Outbreaks of Cryptosporidiosis Associated with Recreational Waters in the United States. ...... 27 

Giardia Taxonomy ...................................................................................................................... 28 

Giardia Infection Occurrence in U.S. Populations ...................................................................... 32 

Outbreaks of Giardiasis Associated with Recreational Waters in the United States. .................. 34 

Table III.1.1-1. Survival of E. coli O157:H7 in Ambient Waters ......................................................................... 38 

Figure II.2.1-1. 

Figure II.2.2-1. 

Reported Cryptosporidium infections in the United States, 1999 to 2005. ................................. 26 

Reported Giardia cases in the 50 states plus Washington DC, 1992 to 2005. ............................ 32 
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ACRONYMS

AEC attaching E. coli

AIDS Acquired Immune Deficiency Syndrome 

AWQC ambient water quality criteria 

BEACH Act Beaches Environmental Assessment and Coastal Health Act of 2000 

CDC U.S. Centers for Disease Control and Prevention 

CPV C. parvum virus 

CWA Clean Water Act 

DAEC diffuse adherent E. coli

DEC diarrheagenic E. coli 

EAggEC enteroaggregative E. coli 

EEC effacing E. coli

EHEC enterohemorrhagic E. coli

EPA U.S. Environmental Protection Agency 

EPEC enteropathogenic E. coli

ETEC enterotoxigenic E. coli

GI gastrointestinal 

GLV Giardia lamblia virus 

GBS Guillain-Barré Syndrome 

HC hemorrhagic colitis 

HEV hepatitis E virus 

HUS hemolytic uremic syndrome 

IPSID immunoproliferative small intestinal disease 

MALT mucosa-associated lymphoid tissue 

NA not available or not applicable 

PCR polymerase chain reaction 

POTW Publicly Owned Treatment Works 

ppt parts per thousand (salinity) 

RFLP restriction fragment length polymorphism 

SPE serial passage experiment 

STEC Shiga toxin-producing E. coli 

U.S. United States 

U.K. United Kingdom 

USDA U.S. Department of Agriculture 

UV ultraviolet (light) 

VTEC verocytotoxin-producing E. coli

WHO World Health Organization (United Nations) 
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EXECUTIVE SUMMARY

Introduction

The overall goal of the current Clean Water Act (CWA) §304(a) ambient water quality criteria 

(AWQC) for bacteria in the United States is to provide public health protection from 

gastrointestinal (GI) illness (gastroenteritis) associated with exposure to fecal contamination 

during recreational water contact. Water quality criteria are specified throughout the world in 

terms of concentrations of fecal indicator organisms because fecal matter can be a major source 

of pathogens in ambient water and because it is not practical or feasible to monitor for the full 

spectrum of all pathogens that may occur in water. For decades, these fecal indicator organisms 

have served as surrogates for potential pathogens and subsequent health risks in both recreational 

and drinking waters. 

The U.S. Environmental Protection Agency (EPA) currently recommends AWQC for 

recreational water that encompass all fecal sources that contain the relevant indicator species 

(enterococci and E. coli). This approach assumes that animal fecal material is as hazardous as 

human fecal material. There is limited evidence, however, that recreational water contaminated 

with animal fecal material is less risky to swimmers than recreational water contaminated with 

human fecal material. 

In order to evaluate the potential risks posed by animal fecal contamination, EPA is interested in 

understanding what human illnesses are caused by swimming in waters contaminated with 

animal fecal material ranging from wildlife sources to agricultural inputs. The animal species of 

most interest are the warm-blooded animals (mammals and birds) whose fecal material is 

detected by current indicators. 

The purpose of this white paper is to provide a summary of information on waterborne zoonotic 

pathogens that come primarily from warm-blooded animals, and which can be used to 

conceptualize potential risks from warm-blooded animal feces in ambient (untreated) 

recreational waters. 

Approach 

Seventy pathogens from warm-blooded animals were evaluated for their potential to be both 

waterborne and zoonotic. Twenty of the 70 pathogens evaluated had all 4 of the following 

attributes: 

1. The pathogen spends part of its lifecycle within one or more warm-blooded animal 

species. 

2. Within the lifecycle of the pathogen, it is probable or conceivable that some life stage will 

enter water. 

3. Transmission of the pathogen from animal source to human is through a water related 

route. 

4. The pathogen causes infection or illness in humans. 
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Six of the 20 waterborne, zoonotic pathogens from warm-blooded animals were selected for 

further discussion based on their relevance in the United States. Five were selected based on 

their potential for outbreaks in ambient (untreated) recreational water and one (Salmonella) was 

included based on outbreaks in drinking water. 

Some well-known waterborne pathogens were excluded from analysis because they are not 

zoonotic. Excluded pathogens include bacteria that are generally found in the environment, freeliving protozoa, viruses, and helminthes that have cold-blooded hosts (e.g., snails, copepods). 

Some common zoonotic pathogens were also excluded because they do not have welldocumented waterborne transmission (i.e., primarily transmitted via soil, food, or drinking 

water). 

Pathogens interact with the ambient environment, other microorganisms, plants, and with their 

hosts. The behavior of pathogens in ambient waters is often different from the behavior of 

indicators in ambient water. The most common environmental factors studied for their impact 

on pathogen survival in water are pH, salinity, light exposure, and temperature. Additional 

environmental characteristics that may influence pathogen survival, infectivity, and virulence 

include the following: ultraviolet (UV) light (duration, intensity), rainfall, runoff, dispersal, 

suspended solids, turbidity, nutrients, organic content, organic foams, water quality, biological 

community in water column, water depth, stratification, mixing (e.g., wind and waves), presence 

of aquatic plants, biofilms, and predation. 

There is evidence that zoonotic pathogens may change in infectivity, virulence, and the severity 

of disease caused in humans depending on their previous host environment. There is also 

evidence that some of these host-factor changes can influence subsequent infection cycles in 

exposed hosts. The key mechanisms of phenotypic change in pathogens are genetic diversity 

(coinfection and quasispecies), cryptic genes, mutators, and epigenetic effects. 

Six Key Waterborne Zoonotic Pathogens 

Pathogenic E. coli

E. coli is an important waterborne bacterial zoonosis because many human pathogenic strains 

occur in livestock and wildlife feces and can survive in ambient waters. In addition, the potential 

illnesses caused by pathogenic E. coli can be severe or fatal. Mortality estimates range from 

0.08 to 1.9 percent of E. coli O157:H7 infections. Children are more at risk than healthy adults 

to suffer more severe outcomes. Between 1991 and 2004, 14 outbreaks of E. coli-related illness 

have been associated with ambient recreational waters. E. coli O157:H7 can survive for at least 

several weeks in animal feces and slurries and has been demonstrated to survive at least 500 days 

at -20 °C in frozen soil. 

Campylobacter 

Campylobacter is a well-known foodborne bacterial pathogen that is commonly associated with 

poultry and livestock. There are also wildlife hosts. Although few waterborne outbreaks have 

been reported, there is potential for Campylobacter to cause recreational water-related illness. 

Normally, infection results in diarrhea that is self-limiting; however, approximately 1 out of 

1,000 infections results in Guillain-Barré syndrome, which is a serious nervous system affliction. 
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Reactive arthritis is also a possible chronic sequela of Campylobacter infection. Campylobacter

has been shown to survive in aquatic environments with low temperatures (4°C) up to 4 months. 

Salmonella 

Salmonella is also a well-known foodborne bacterial pathogen that is associated with poultry and 

livestock. There are also wildlife hosts. Elevated levels of Salmonella have been observed in 

major water bodies that receive discharges of meat processing wastes, raw sewage, farming 

operations, and effluents from ineffective sewage treatment plants. The clinical symptoms of 

salmonellosis may include diarrhea, abdominal pain, nausea, chills, and fever. Between 1991 

and 2002, 3 waterborne outbreaks were attributed to nontyphoid Salmonella; Salmonella were 

the etiologic agent in 0.9 percent of 259 recreational waterborne outbreaks occurring from 1971 

to 2000. Under suitable environmental conditions, Salmonella can survive for weeks in waters 

or years in soils. 

Leptospira 

Leptospira is an important waterborne bacterial pathogen for most of the world. Because 

warmer climates favor its survival in the environment, the highest incidence of leptospirosis in 

the United States is found in Hawaii. The source of infection in humans is usually either direct 

or indirect contact with the urine of an infected animal. There are numerous symptoms 

associated with leptospirosis, but the more severe form is known as Weil’s disease. In addition, 

acute infection during pregnancy has been reported to cause abortion and fetal death. From 1971 

to 2000, 16 percent of recreational waterborne disease outbreaks in the United States were 

attributed to Leptospira. In 1998, an outbreak (375 cases) of leptospirosis was reported that was 

associated with a triathlon in a lake in Illinois. 

Cryptosporidium 

Cryptosporidium is a well-known waterborne protozoan pathogen. EPA currently regulates it 

under the Safe Drinking Water Act because the level of Cryptosporidium in many ambient 

source waters is sufficiently high that risks to drinking water must be managed. 

Cryptosporidium infection has been reported in more than 155 mammalian species and numerous 

reptiles, amphibians, birds, and fish. In watersheds with diverse land-use patterns, it is likely that 

different sources contribute different proportions to the total contamination load at different 

times during the year, with the relative contributions depending on a wide range of watershed 

characteristics. Cryptosporidiosis is primarily characterized by GI symptoms such as profuse, 

watery diarrhea. Immunocompromised individuals generally experience chronic gastroenteritis, 

which may last as long as the immune impairment. The largest known outbreak of 

cryptosporidiosis occurred in 1993 in Milwaukee, Wisconsin and infected 403,000 individuals. 

Animal fecal contamination of drinking water was indicated in the outbreak. In the United 

States, from 1991 to 2004, 6 outbreaks of cryptosporidiosis have been associated with untreated 

recreational waters. Excreted Cryptosporidium oocysts can survive for substantial periods in 

animal wastes and soils. Thus, contaminated runoff can enter ambient water and result in 

potential human exposures. The majority of oocysts (99 percent) are inactivated by repeated 

freeze-thaw cycles; therefore, Cryptosporidium may be environmentally limited in parts of the 

United States during winter months. Between 4 and 20° C, there is very little inactivation of 

oocysts in different types of agricultural soils. Oocyst survival in various water matrices is 

highly variable, but survival for longer than 30 days has been demonstrated in several studies. 
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Giardia 

Giardia is also a well-known waterborne protozoan pathogen. Although both livestock and 

humans have been implicated in contaminating water sources with Giardia, humans are 

responsible for the majority of the contaminations. Zoonotic transfer plays only a minor role in 

the infection cycles of Giardia, and animal contact is not a major risk factor. There is a wide 

spectrum of symptoms associated with giardiasis that ranges from asymptomatic infection and 

acute self-limiting diarrhea to persistent chronic diarrhea, which sometimes fails to respond to 

treatment. Asymptomatic infection is very common, with 50 to 75 percent of infected persons 

reporting no symptoms. In the United States, from 1991 to 2004, 7 reported outbreaks of 

giardiasis were associated with untreated recreational waters. At 4° C, Giardia cysts were 

infective for 11 weeks in water, 7 weeks in soil, and 1 week in cattle feces. 

Summary 

Although the most common waterborne recreational illnesses are probably due to nonzoonotic 

human viruses, which typically cause short-term gastroenteritis, the waterborne zoonotic 

pathogens discussed in this report have the potential to cause serious health effects—especially 

in immunocompromised persons and subpopulations. While serious health outcomes are likely 

to be rare in comparison with self-limiting illnesses as a result of ambient (recreational) water 

exposure, the adverse health impacts of the rare, but more serious illnesses remain an important 

public health challenge. 
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I. BACKGROUND AND INTRODUCTION

I.1 Background: Context and Purpose 

Since the U.S. Environmental Protection Agency (hereafter EPA or the Agency) last published 

recreational water quality criteria in 1986, there have been significant scientific and technical 

advances, particularly in the areas of molecular biology, microbiology, and analytical chemistry. 

EPA believes that these advances need to be considered and evaluated for feasibility and 

applicability in the development of new or revised CWA §304(a) criteria for recreational water. 

To this end, EPA has been conducting research and assessing relevant information to provide the 

scientific and technical foundation for the development of new or revised criteria. The 

enactment of the Beaches Environmental Assessment and Coastal Health (BEACH) Act of 2000 

(which amended the CWA) required EPA to conduct new studies and to issue new or revised 

criteria for Great Lakes and coastal marine waters. 

In response to the BEACH Act of 2000, EPA also has engaged a range of stakeholders 

representing the general public, public interest groups, state and local governments, industry, and 

municipal wastewater treatment professionals. In March 2007, EPA convened a group of 43 

national and international technical, scientific, and implementation experts from academia, 

numerous state agencies, public interest groups, EPA, and other federal agencies at a formal 

workshop to discuss the state of the science on recreational water quality research and criteria 

implementation. Among the input from the individuals attending the workshop were suggestions 

for incorporating the ability to differentiate sources of fecal contamination and to determine the 

relative human health risk from these sources into the new or revised criteria. 

Based on the feedback from the large group of stakeholders, as well as input and 

recommendations from the scientific community, the Agency has developed a Critical Path 

Science Plan for Development of New or Revised Recreational Water Quality Criteria. One of 

the key questions posed in the science plan asks: what is the risk to human health from 

swimming in water contaminated with human fecal matter as compared to swimming in water 

contaminated with nonhuman fecal matter? Human and animal feces can both potentially 

contain pathogens that cause human illness. Some human pathogens are host-specific (i.e., 

human enteric viruses), while other human pathogens are found in and can be shed by both 

humans and other animals. Moreover, while all enteric pathogens of humans are infectious to 

other humans, only a subset of the enteric pathogens of animals is infectious to humans. 

Understanding which pathogens could be present depending on the source of fecal contamination 

might allow the Agency to better estimate human health risks from identified sources of fecal 

matter. 

EPA’s current recommended recreational water quality criteria for microbes treat human health 

risks from the various sources of fecal contamination as equivalent (USEPA, 1986). These 

criteria are based on the risk of illness from swimming in waters influenced by sewage treatment 

plants effluents. Health risks from other sources (e.g., poorly-treated or untreated human waste, 

nonhuman sources of fecal contamination, mixed sources such as urban stormwater runoff) were 

not well understood at the time the 1986 criteria were developed, and EPA’s approach was to be 

protective of human health regardless of the source. EPA recognizes, however, that the health 
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February 2009 6 

risk from sources other than sewage treatment plants may be different and that the scientific 

advances over the intervening years may now allow the Agency to better characterize the relative 

risks to human health from these various sources of fecal contamination. Specifically, the 

Agency is interested in understanding which human illnesses can be caused by swimming in 

waters contaminated with nonhuman fecal matter including both wildlife sources and agricultural 

inputs. The animal species of most interest are the warm-blooded animals (mammals and birds) 

for which fecal matter is detectable by current fecal indicators. 

The purpose of this white paper is to provide summary information on waterborne zoonotic 

pathogens that come primarily from warm-blooded animals, and which can be used to 

conceptualize potential risks to humans from warm-blooded animal feces in recreational waters. 

I.2 Introduction 

In the development of health protective criteria for recreational waters, pathogen contamination 

is the central concern, and fecal matter can be a major source of pathogens in ambient water. 

Current recreational AWQC are designed specifically to protect humans from GI illness 

(gastroenteritis) associated with exposure to fecal contamination in recreational waters (USEPA, 

1986). Because widespread monitoring of recreational waters directly for all disease-causing 

microorganisms (especially pathogenic bacteria, viruses, and protozoa) remains infeasible, public 

health and environmental protection agencies have relied on the detection of fecal indicator 

organisms, which comprise a few groups of nonpathogenic fecal bacteria and some viruses, to 

indicate the presence and magnitude of fecal material. This approach assumes that waterborne 

pathogens co-occur with the fecal material. “More specifically, fecal indicator bacteria provide 

an estimation of the amount of feces, and indirectly, the presence and quantity of fecal pathogens 

in the water” (NRC, 2004). Therefore, use of bacterial indicators is predicated on the 

presumption that there are no significant environmental sources of these microorganisms (i.e., 

nonenteric sources). However, this presumption is not entirely valid; fecal indicator organisms 

have been demonstrated to have natural reservoirs in the aquatic environment where they can 

survive for extended periods and even proliferate (e.g., fecal indicator bacteria in U.S. coastal 

[Yamahara et al., 2007] and Great Lake waters and sand [Whitman et al., 2006]). 

Historically, EPA has recommended that recreational water quality criteria encompass all fecal 

sources of pathogens that contain the relevant indicator microbes. This recommendation is based 

on the regulatory premise that animal-derived (zoonotic) human pathogens in fecally 

contaminated waters are as hazardous as their human-derived counterparts (Schaub, 2004). This 

presumption is supported by current research that confirms that there are many waterborne 

zoonotic bacteria and protozoa common to both humans and animals, especially mammals 

(WHO, 2004). Research also suggests, however, that there may be some attenuation of 

infectivity, virulence, and disease severity to humans from animal-derived human pathogens (see 

Section III.2). In addition, there are many pathogens that could be zoonotic, fecal, and/or 

waterborne, but these routes of transmission have not yet been conclusively demonstrated. 

Given the scientific advancements in pathogen characterization since EPA’s 1986 AWQC were 

released, it is appropriate to examine the broadest array of currently known and suspected 

waterborne, fecal, and zoonotic pathogens and their human health impacts. These include 
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February 2009 7 

primarily bacteria, viruses, protozoa, and helminths. There are many zoonotic pathogens and

many waterborne pathogens; however, there is a more limited subset of pathogens that are both. 

For this report, the following attributes were used to select the waterborne, zoonotic pathogens of 

concern (partially adapted from Bolin et al., 2004a): 

1. The pathogen must spend part of its lifecycle within one or more warm-blooded animal 

species. 

2. Within the lifecycle of the pathogen, it is probable or conceivable that some life stage will 

enter water. 

3. Transmission of the pathogen from animal source to human must be through a water

related route. There are zoonotic pathogens for which waterborne exposure has not been 

detected as a significant route of cross-species transmission. This does not exclude the 

possibility that these zoonotic pathogens could be transmitted via water. 

4. The pathogen must cause infection or illness in humans. There are animal pathogens that 

have waterborne transmission between animals yet are not known to cause illness in

humans. 

There are many waterborne zoonotic pathogens that exhibit all four attributes listed above. See 

Appendix A, Table A-1, for a summary of waterborne pathogens that meet the above criteria and 

selected pathogens that meet some, but not all, of the above criteria. 

The remainder of this paper is organized into two main sections. Section II characterizes six key 

groups of zoonotic pathogens for which there is evidence of human health risks from recreational 

exposure via ambient waters. Section III presents an overview of how the key pathogens interact 

with their environment, which includes both the water environment and the host animals. 
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II. KEY WATERBORNE ZOONOTIC PATHOGENS OF CONCERN

Based on a review of the literature and other information sources (Appendix B), 6 of the 20 

pathogens identified as waterborne and zoonotic from warm-blooded animals stood out as having 

the most evidence for human health impacts due to recreational exposures in the United States. 

The six pathogens discussed in this paper in more detail are pathogenic E. coli, Campylobacter, 

Salmonella, Leptospira, Cryptosporidium, and Giardia. This list correlates well with the top five 

waterborne pathogens for recreational and drinking waters. The top five waterborne pathogens 

for recreational water are E. coli, Campylobacter, Leptospira, Cryptosporidium, and Giardia, 

while the top five for drinking water are E. coli, Campylobacter, Salmonella, Cryptosporidium, 

and Giardia (Craun et al., 2004a). The waterborne zoonosis potential of viruses also is discussed 

because viruses may be emerging waterborne zoonoses. 

For each of the six key pathogens, information on strain variation, known zoonoses, route(s) of 

exposure, illness symptoms, and disease incidence are discussed in the sections that follow. 

Because incidental ingestion is the primary route of recreational exposure to pathogens, 

summary information on incidental ingestion is provided in Appendix C. 

II.1 Bacteria 

II.1.1 Escherichia coli 

E. coli is an important waterborne zoonosis because human pathogenic strains occur in livestock 

and wildlife feces and can survive in ambient water. In addition, the potential illnesses caused 

by pathogenic E. coli can be severe or fatal, especially in immuncompromised persons and 

subpopulations. Pathogenic E. coli is also a well-documented foodborne pathogen (USDA, 

2001). Although pathogenic E. coli have been found in treated wastewater effluents in the 

United States (Boczek et al., 2007), waterborne outbreaks are not as prevalent as foodborne 

cases. 

E. coli Strain Variation 

Benign strains of E. coli are a part of the normal microbial flora present in the colons and feces 

of all warm-blooded animals. However, multiple disease causing serotypes of E. coli have been 

identified in the past few decades. The most well-known serotype is E. coli O157:H7, which 

frequently occurs in wastewater and feces in developed countries and can result in severe 

illnesses and death. E. coli O157:H7 (or just O157:H7) is the “poster child” for pathogenic E. 

coli and is the serotype most extensively investigated (Chart et al., 2000). 

E. coli is a versatile bacterium and multiple subtypes and strains that are pathogenic have been 

documented. Although the nomenclature for these strains has not yet stabilized in the literature, 

Mølbak and Scheutz (2004) provided the following helpful summary of the current 

nomenclature: 

• Diarrheagenic E. coli (DEC) – includes all the strains on this list; 
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• Verocytotoxin (Shiga toxin)-producing E. coli (VTEC or STEC) – E. coli that produce 

verocytotoxin (Shiga toxin) VT1 and/or VT2; 

o Enterohemorrhagic E. coli (EHEC) – originally defined as serotypes that cause a 

clinical illness similar to E. coli O157:H7, now used as a term for VTEC that 

cause hemorrhagic colitis (HC) in humans; 

• Enterotoxigenic E. coli (ETEC) – E. coli that produce enterotoxins that are heat stable 

(STh, STp) and/or heat labile (LT); 

• Attaching and effacing E. coli (A/EEC) – E. coli that attach to and efface the microvilli of 

enterocytes, but do not produce high levels of verocytotoxin; 

o Enteropathogenic E. coli (EPEC) – Subtype of A/EEC, usually of particular 

serotypes that mostly contain an EPEC adherence factor plasmid and often 

produce bundle-forming pili; 

• Enteroaggregative E. coli (EAggEC) – E. coli that exhibit a pattern of aggregative 

adherence to tissue culture; and 

• Diffuse adherent E. coli (DAEC) – E. coli that exhibit a pattern of diffuse adherence to 

tissue culture. 

Nataro and Kaper (1998) provide a comprehensive, albeit dated, review of the DEC. 

E. coli Zoonotic Potential 

E. coli is part of the normal intestinal flora of humans and warm-blooded animals and can readily 

spread to humans through contaminated food and water (WHO, 2004). Pathogenic E. coli have 

been documented in a wide variety of animal species including cattle (Chapman et al., 1997; 

Rangel et al., 2005), chickens (Schoeni and Doyle, 1994), sheep (Chapman et al., 1997; Kudva et 

al., 1996), pigs (Booher et al., 2002; Chapman et al., 1997; Feder et al., 2003), deer (Keene et al., 

1997; Rice et al., 1995; Sargeant et al., 1999), horses (Chalmers et al., 1997), and dogs 

(Hammermueller et al., 1995). 

Ruminants, and cattle in particular, are considered one of the most important animal sources of

E. coli O157:H7 and other VTECs. All of the VTECs including EHEC are capable of causing 

severe disease in humans, are typically shed by healthy cattle and other species, and have 

documented cases of transmission via humans and water (Mølbak and Scheutz, 2004). Chapman 

et al. (1997) determined that the monthly prevalence of E. coli O157:H7 in cattle ranged from 

4.8 to 36.8 percent, which was higher than the prevalence range in poultry, sheep, and pigs. 

Michel et al. (1999) examined the relationship between 3,001 cases of VTEC and the livestock 

density in rural areas of Ontario, Canada. Their research indicated that cattle density had a 

positive and significant association with the number of reported cases of VTEC in humans, 

suggesting that living near cattle farms may increase a person’s risk of contracting VTEC. 

Current data suggest that the prevalence of E. coli O157:H7 in poultry is low (Chapman et al., 

1997), although contact with chickens has resulted in outbreaks. Schoeni and Doyle (1994) 

inoculated 1-day-old chicks with strains of serotype O157:H7. The chicks shed serotype 

O157:H7 up to 11 months after inoculation, and O157:H7 was subsequently recovered from their 

egg shells, but not from the yolks or whites. In an outbreak in northern Italy, the source of 

exposure was believed to be chickens in 15 cases of hemolytic uremic syndrome (HUS; see more 
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February 2009 10 

below) that were caused by serotype O157 and other EHEC serotypes (Tozzi et al., 1994). In 

this outbreak, a case-controlled study showed an association between contact with chickens and 

HUS although VTEC was not isolated from any of the chickens. 

In a study by Chapman et al. (1997), O157:H7 was isolated from 2.2 percent of sheep and 4 

percent of pigs, respectively. In a Russian study, O157:H7 was found in sheep, and the incidence 

was highly variable, ranging from 31 percent in June to 0 percent in November (Kudva et al., 

1996). Kudva and colleagues also showed that 80 percent of the O157:H7 isolates had at least 

two of the Shiga-like toxin types I or II or the attaching-effacing lesion genes. Strains that 

produce Shiga-like toxins have been documented in humans and in animals (Kudva et al., 1996; 

Mølbak and Scheutz, 2004). 

E. coli Route of Exposure

Waterborne transmission of E. coli O157:H7 has been reported from both recreational water 

(Ackman, 1997; CDC, 2002; McCarthy et al., 2001; Samadpour et al., 2002; Yoder et al., 2004) 

and contaminated drinking water (CDC, 2002; Hrudey et al., 2002, 2003; Olsen et al., 2002; 

Pond, 2004; Swerdlow et al., 1992; Yarze and Chase, 2000). Most studies examining 

contamination from recreation immersion have suggested that ingestion was the primary route of 

exposure (Keene et al., 1994). Because E. coli O157:H7 has a relatively low infectious dose, 

swallowing a small amount of contaminated water may cause illness (Haas et al., 2000; Keene et 

al., 1994). 

Immersion in and ingestion of recreational waters has been the route of exposure for strains of E. 

coli other than EHEC (Yoder et al., 2004). In Connecticut, 11 persons were infected with E. coli 

O121 in an outbreak associated with swimming in a lake (CDC, 2000). 

E. coli Illness Symptoms

E. coli can cause a relatively wide range of illness symptoms, depending on the strain and the 

underlying health of the host (Hunter, 2003; Mølbak and Scheutz, 2004). Incubation periods 

vary and can be as short as 8 hours for EAEC infections (Nataro et al., 1995), 14 to 50 hours for 

ETEC (Dupont et al., 1971), and 3 to 4 days for EHEC, with shorter (1 to 2 days) and longer (5 

to 8 days) incubations noted in some outbreaks (Nataro and Kaper, 1998). Approximately 82 to 

95 percent of all E. coli cases result in relatively minor illness symptoms including abdominal 

cramps, vomiting, diarrhea (often bloody), and sometimes fever (Ostroff et al., 1989; Swerdlow 

et al., 1992). The duration of these symptoms is 4 to 10 days (CDC, 1993a) although, in the 

Cincinnati outbreak, infants remained hospitalized for 21 to 120 days (Nataro and Kaper, 1998). 

Symptoms may be more severe for persons with hemorrhagic colitis (HC) or bloody 

inflammation of the colon (Griffin and Tauxe, 1991). 

Symptoms commonly associated with human illness from the various DEC include the 

following: 

• VTEC (or STEC) – Diarrhea, hemorrhagic colitis, HUS; 

o EHEC – hemorrhagic colitis (HC); 
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February 2009 11 

• ETEC – Acute watery diarrhea; 

• A/EEC – Acute or persistent diarrhea; 

o EPEC – Acute or persistent diarrhea; 

• EAggEC – Acute watery, often protracted diarrhea; and 

• DAEC – Acute or persistent diarrhea. 

In rare cases, HC can develop into HUS, which is a severe life-threatening disease that can result 

in kidney failure and neurological complications such as seizures and strokes (Brotman, 1995). 

Brooks et al. (2005) conducted a study that suggests E. coli strains that produce Shiga toxin 2 are 

much more likely to result in HUS than strains that only produce Shiga toxin 1. Approximately 

2 to 7 percent of all E. coli O157:H7 infections result in HUS, and HUS is most common among 

children under 5 years old and the elderly (Griffin and Tauxe, 1991; WHO, 2004). Less than 10 

percent of HUS cases turn into a chronic illness such as chronic kidney failure, blindness, or 

partial paralysis (Tarr, 1995). Approximately 33 percent of persons that contract HUS have 

abnormal kidney function for several years, sometimes requiring long-term dialysis (WHO, 

2004). In very rare cases, HUS can also lead to death. Cases of infection with E. coli O157:H7 

from swimming-associated outbreaks, compared to other routes of exposure, have the highest 

rate of HUS. This difference may be due to the higher proportion of young children participating 

in swimming and becoming infected during such outbreaks and the higher likelihood of young 

children developing HUS (Rangel et al., 2005). HUS, non-bloody diarrhea, and HC may occur 

with O157:H7 infections; other complications may include cholecystitis, colonic perforation, 

intusssception, pancreatitis, posthemolytic biliary lithiasis, post-infection colonic stricture, rectal 

prolapse, appendicitis, hepatitis, hemorrhagic cystitis, pulmonary edema, myocardial 

dysfunction, and neurological abnormalities(Nataro and Kaper, 1998). 

As noted above, infection with E. coli O157:H7 can also result in death. The U.S. Centers for 

Disease Control and Prevention (CDC) estimates a death rate of 0.08 percent, although case 

studies reveal slightly higher rates. For example, the 1993 fast-food E. coli O157:H7 outbreak in 

Washington, California, Idaho, and Nevada resulted in 4 deaths out of approximately 700 who 

fell ill, which corresponds to approximately 0.57 percent mortality (Brotman, 1995). Griffin and 

Tauxe (1991) reviewed 12 outbreaks in the United States between 1982 and 1990 and calculated 

a mortality rate of 1.9 percent among those with diagnosed E. coli O157:H7 infections. 

E. coli Illness Incidence 

The CDC estimates that there are 73,000 cases of E. coli 0157:H7 infections and 61 deaths 

annually in the United States. Non-O157 Shiga-like toxin serotypes cause approximately 37,000 

illnesses per year (Mead et al., 1999).1

 Craun et al. (2004a) estimated that E. coli was the 

etiological agent for 30 percent of the outbreaks from zoonotic contamination in untreated 

recreational waters from 1971 to 2000. 

E. coli O157:H7 infection associated with recreational exposure was first reported in June 1991 

in a lake in Oregon (Keene et al., 1994). From 1991 until 2002, 20 additional outbreaks as a 

result of exposure to contaminated recreational waters have been reported to the CDC (Rangel et 

 1

 The CDC is currently updating these numbers, but the newest values have not yet been released. 
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February 2009 12 

al., 2005). Fourteen of the outbreaks occurred as a result of exposure to contaminated lakes or 

ponds, while seven occurred from exposure to contaminated swimming pools (Rangel et al., 

2005). 

CDC’s surveillance system probably captures a small proportion of E. coli O157:H7 outbreaks 

that occur because many illnesses are not reported to public health officials or the CDC, are not 

recognized as E. coli infections, or the outbreak is considered of unknown etiology (Cieslak et 

al., 1997). 

From 1991 to 2004, 14 outbreaks of E. coli related illness have been associated with untreated 

recreational waters (Table II.1.1-1). 

II.1.2 Campylobacter 

Campylobacter Strain Variation 

Of the 17 species in the genus Campylobacter, C. jejuni, and C. coli are the most important 

human pathogens. Eight strains of C. jejuni have been DNA sequenced. At least two strains of 

C. jejuni have been shown to cause illness in ferrets, mice, rabbits, and rats, and several of the 

strains have been associated with Guillain-Barré syndrome (GBS) (Nachamkin, 2002). 

Table II.1.1-1. Outbreaks of E. coli Associated with Recreational Waters in the United States 

Year Number of Cases Number of Outbreaks Source of Outbreak(s) 

1991 80 1 Lake 

1992 0 0 NA 

1993 0 0 NA 

1994 166 1 Lake 

1995 28 4 Lakes 

1996 24 2 1 pool, 1 lake 

1997 8 1 Lake 

1998 31 2 1 pool, 1 lake 

1999 61 5 1 pool, 3 lakes, 1 ditch water 

2000 0 0 NA 

2001 49 2 Lakes 

2002 9 1 Pool 

2003 0 0 NA 

2004 0 0 NA 

Source: Data from CDC Surveillance Summaries: Morbidity and Mortality Weekly Report (MMWR) 

Surveillance for Waterborne-Disease Outbreaks - United States: 1991-1992, 1993-1994, 1995-

1996, 1997-1998, 1999-2000, 2001-2002, 2003-2004 (CDC, 1993b, 1996, 1998, 2000, 2002, 2004, 

2006). 
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Campylobacter Zoonotic Potential 

Because most of the published literature focuses on food contamination from human waste as the 

primary risk factor for Campylobacter infection, some professionals in the health community 

have concluded that the zoonotic waterborne route is unlikely to be important (Till and McBride, 

2004). Some evidence indicates that the human sources of Campylobacter may obscure the 

zoonotic risk factors (McBride, 1993). 

McBride et al. (2002) found that 60 percent of all samples collected from 25 freshwater 

recreational water sites in New Zealand over 15 months contained at least one species of 

Campylobacter. This finding led to an inference that 4 percent of all campylobacteriosis cases in 

New Zealand were due to water contact recreation (McBride et al., 2002). Donnison and Ross 

(2003) note that nearly all streams near dairy farms in New Zealand contain Campylobacter, and 

despite generally low concentrations, these streams may help cycle Campylobacter in farm 

animals and indirectly contribute to the high incidence of human infection in New Zealand. 

The species and strain of Campylobacter contained in a stream is highly influenced by the path 

of the stream, with surface waters running through beef- and sheep-grazing pastures typically 

contaminated with C. coli and C. jejuni (Jones, 2001). Surface waters that have contact with 

avian species are typically contaminated with C. jejuni, C. lari, C. coli, and avian-sourced 

urease-positive thermophilic campylobacters (Jones, 2001). The main source of campylobacters 

for bathing waters is typically assumed to be sewage effluent, though there is evidence that birds 

may be primarily responsible for contamination (Jones, 2001). 

Campylobacter Route of Exposure 

The main route of exposure to Campylobacter from recreational waters is from incidental 

ingestion of water during full immersion activities such as swimming. The bacteria may be of 

anthropogenic or animal sources. From 1991 to 2002, 3 percent of waterborne outbreaks were 

attributed to Campylobacter (7 outbreaks, 360 cases) (Craun et al., 2006). Craun et al. (2005) 

summarized and discussed 259 waterborne outbreaks occurring in the United States from 1971 to 

2000 and associated only with recreational water. Campylobacter was the etiologic agent for 0.9 

percent of the outbreaks. Although waterborne sources of Campylobacter are important, most 

infections occurred as a result of handling contaminated foods (e.g., raw chicken) and direct 

person-to-person transmission is rare (Allos, 2001). 

Campylobacter Illness Symptoms 

Campylobacter infection can result in a number of symptoms, including loose and watery or 

bloody diarrhea, dysentery, fever, and severe abdominal cramps (Allos, 2001; Fricker, 2006a). 

Infections of Campylobacter are symptomatically indistinguishable from those of other bacterial 

pathogens such as Salmonella (Nachamkin, 2002). Diarrheal symptoms may be frequent at the 

peak of the illness, typically occurring 8 to 10 times per day. Although the disease usually lasts 

only one week, some infected individuals experience relapses leading to several weeks of 

symptoms (Allos, 2001). 
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February 2009 14 

Some complications may result from Campylobacter infection including cholecystitis, 

pancreatitis, peritonitis, and massive GI hemorrhage. Some immunocompromised individuals 

experience bacteremia as a result of campylobacteriosis, and in rare instances, some individuals 

have experienced meningitis, endocarditis, septic arthritis, osteomyelitis, or neonatal sepsis. 

Infection rarely results in death, with 1 death per 20,000 infections (Allos, 2001). 

Several chronic sequelae have been associated with Campylobacter infection including the 

development of GBS (Fricker, 2006a). GBS is an acute demyelinating disease of the peripheral 

nervous system that affects 3,000 to 6,000 people in the United States annually, with 

approximately 1,000 to 2,000 cases preceded by C. jejuni infection (Allos, 1998). The risk of 

developing GBS after C. jejuni infection, however, is small (approximately 1 case of GBS per 

1,000 infections), and many GBS-related C. jejuni infections are asymptomatic (Allos, 2001). 

Reactive arthritis and depression also have been reported as chronic sequelae following 

campylobacteriosis (Garg, 2006; Nachamkin, 2002). Recent evidence has associated C. jejuni

with a rare form of mucosa-associated lymphoid tissue (MALT) lymphoma called 

immunoproliferative small intestinal disease (IPSID); campylobacteriosis has not yet been shown 

as causative agent of IPSID (Poly and Guerry, 2008). 

In 2000, a municipal water supply in Walkerton Ontario became contaminated with E. coli and 

C. jejuni. In the outbreak that resulted from that contamination, persons who showed symptoms 

of acute bacterial gastroenteritis at the time of the outbreak were more likely to exhibit 

hypertension and reduced kidney function approximately 4 years after infection than those who 

were asymptomatic at the time of the outbreak (Garg et al., 2005). 

Campylobacteriosis Incidence 

Although Campylobacter became a reportable illness in the United States in the early 1980s, it is 

estimated that only 1 in 38 cases of detected infection actually are reported (Mead et al., 1999). 

Approximately 2.4 million Campylobacter infections are estimated to occur in the United States 

every year (Allos, 2001). Between 1996 and 1999, the incidence of campylobacteriosis in the 

United States declined by 26 percent, from 23.5 to 17.3 cases per 100,000 people (Allos, 2001). 

According to reports from 1999, Britain experiences approximately 5 times this infection rate 

(103.7 cases per 100,000 people), though reporting rates may not be comparable (Gillespie et al., 

2002). C. jejuni infection is one of the most common causes of gastroenteritis across the world 

and is frequently responsible for diarrheal illness in travelers (Allos, 2001).

Other than an outbreak in 1999, in Florida, where 6 cases of C. jejuni infections resulted from a 

private swimming pool, no other recreational waterborne outbreaks have been reported to the 

CDC between 1991 and 2004 (CDC, 2002). 

II.1.3 Salmonella 

Salmonella Strain Variation and Zoonotic Potential 

Salmonella are non-encapsulated, Gram-negative bacteria of the Enterobacteriaceae family that 

infect both animals and humans causing a wide range of illnesses (Cohen, 1986; Lightfoot, 2004; 
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February 2009 15 

Ohl, 2001). There are more than 2,500 serovars/serotypes in the genus Salmonella (Lightfoot, 

2004). 

The genus Salmonella consists of two species, S. enterica and S. bongori. S. enterica is divided 

into the following six subspecies: S. e. enterica; S. e. salamae; S. e. arizonae; S. e. diarizonae; S. 

e. houtenae; and S. e. indica (Lightfoot, 2004). The many serovars in the group are closely 

related to each other by somatic and flagellar antigens, and most strains show diphasic variation 

of flagellar antigens). Thus, Salmonella can be serotyped by means of somatic and flagellar 

antigens and further subtyped by antibiotic-sensitivity testing, biochemical reactions, phagetyping, and analysis of the plasmids they carry. All Salmonella serotypes share the ability to 

invade the host by inducing their own uptake into cells of the intestinal epithelium (Lightfoot, 

2004). Although more than 2,500 Salmonella serotypes exist, only 10 account for more than 70 

percent of the isolates reported annually in the United States (Cohen, 1986; Lightfoot, 2004). 

Because the vast majority of Salmonella isolates from humans are of the subspecies S. e. 

enterica, the CDC recommends that Salmonella strains only be referred to by their genus and 

serotype (e.g., S. typhi). 

S. typhimurium and S. enteritidis are the most prevalent serotypes found in the United States 

(CDC, 2006). The other serotypes have much smaller incidences in the United States; S. 

enteritidis accounted for 10 percent in 1984, and S. newport, S. infantis, and S. heidelberg

accounted for 4.5, 3.0, and 1.0 percent, respectively. 

Some Salmonella serotypes are highly host-specific, restricted to a single host species and rarely 

causing disease in other species (Lightfoot, 2004). S. typhi and S. paratyphi are exclusively 

human pathogens, with no known animal reservoirs, while S. enteriditis and S. typhimurium 

infect a wide range of animal hosts, including poultry, cattle, and pigs. The serotypes with a 

wide range of animal hosts can also infect humans, usually via food consumption, and cause selflimited gastroenteritis in humans (WHO, 2004). S. gallinarum and S. pullorum are almost 

exclusively pathogens of poultry (Cohen, 1986). Human pathogens S. heidelberg and S. litchfield

have primarily avian and reptilian reservoirs, respectively (Cohen, 1986). S. abortusovis is 

specific to sheep (Lightfoot, 2004). Salmonella has also been reported in swine, cattle, rodents, 

birds, turtles, dogs, and cats (Covert and Meckes, 2006). The CDC estimates that 74,000 cases of 

salmonellosis per year are associated with exposure to reptiles or amphibians (directly or 

indirectly) (Lightfoot, 2004). 

In 1993, an outbreak of S. typhimurium where more than 650 people became ill and that resulted 

in 7 deaths, was traced to a water-storage tower that allowed access to birds (Covert and Meckes, 

2006). Although this outbreak was from drinking water rather than recreational water, it 

illustrates the potential for waterborne exposure due to birds. 
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February 2009 16 

Salmonella Route of Exposure 

Salmonella infections begin with the ingestion of organisms in contaminated food or water 

(Lightfoot, 2004; Ohl, 2001). Although ingestion or exposure to infected water from recreational 

swimming is less common, it has been reported worldwide (Cohen, 1986; Lightfoot, 2004). 

Researchers have observed a reduction in the infectious dose of Salmonella under conditions 

where the gastric pH is elevated suggesting that gastric acidity may create an initial barrier to 

infection (Lightfoot, 2004). Salmonella also exhibit an adaptive, acid-tolerance response in low 

pH conditions thereby allowing them to live in acidic host environments like the stomach (Ohl, 

2001). 

Elevated levels of Salmonella also have been observed in major water bodies that receive 

discharges of meat processing wastes, raw sewage, and effluents from ineffective sewage 

treatment plants (Geldreich, 1996). Farming operations with cattle and poultry result in large 

quantities of fecal products in relatively small areas due to the dense population of animals. 

Thus, if the animal waste is not discharged into a lagoon or landfill, the stormwater runoff over 

the animal feedlots will transport massive loads of fecal pollution to the receiving waters of the 

drainage basin (Lightfoot, 2004). 

Salmonella Illness Symptoms 

Illnesses caused by Salmonella range from asymptomatic colonization and mild gastroenteritis to 

the more serious enteric fever (typhoid), meningitis, and osteomyelitis (Cohen, 1986). Enteric 

fever and gastroenteritis are the key clinical syndromes associated with a Salmonella infection 

(Lightfoot, 2004). 

Different Salmonella serovars cause different clinical symptoms. S. typhi causes enteric fever 

(typhoid) in humans, and S. typhimurium causes diarrhea in humans and other animal species but 

a typhoid-like syndrome in mice (Lightfoot, 2004). S. abortusovis is responsible for abortion in 

ewes. Most Salmonella serovars cause an acute and mild enteritis, but S. blegdam, S. bredeney, 

S. choleraesuis, S. dublin, S. enteritidis, S. panama, S. typhimurium, and S. virchow may also be 

invasive and cause pyemic infections localizing in the viscera, meninges, bones, joints, and 

serous cavities (Lightfoot, 2004; Covert and Meckes, 2006). S. dublin is also particularly 

associated with different extraintestinal infections in persons with acquired immunodeficiency 

syndrome (AIDS) (Lightfoot, 2004). 

Infection with S. typhi or S. paratyphi, which are exclusively human pathogens, results in enteric 

fever (Ohl, 2001). Clinical symptoms of enteric fever include diarrhea, abdominal pain, fever, 

and sometimes a maculopapular rash. The pathological sign of enteric fever is mononuclear cell 

infiltration and hypertrophy of the reticuloendothelial system (Ohl, 2001). 

Salmonellosis is caused by ingestion of nontyphoidal salmonellae (e.g., S. enteriditis and S. 

typhimurium) with an incubation period of 8 to 72 hours (Lightfoot, 2004). The estimated 

inoculum size of nontyphoidal Salmonella required to cause symptomatic disease in healthy 

adult volunteers is 105

 to 1010 organisms (Lightfoot, 2004). The infectious dose varies 

depending on the age and health of the person, strain differences, and the vector. Most 
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February 2009 17 

salmonellosis cases are self-limiting, and the affected persons recover without treatment (CDC, 

2006; Cohen, 1986). Some infections are more severe, however, particularly in the young, 

elderly, and people with weakened immune systems, and such infections may become invasive 

(APHA, 2004; Lightfoot, 2004). 

The clinical symptoms of salmonellosis may include diarrhea, abdominal pain, nausea, chills, 

fever, and prostration with the duration of illness ranging approximately 2 to 7 days (APHA, 

2004; WHO, 2004). Vomiting may occur as well, but it is rare and usually a sign of invasive 

disease (APHA, 2004). Organisms that leave the GI tract and invade the rest of the body can 

cause bacteremia and septicemia, thus spreading the salmonellae to many organs in the body and 

possibly leading to abscesses, septic arthritis, cholecystitis, endocarditis, meningitis, pericarditis, 

pneumonia, pyodrema, or pyelonephritis (APHA, 2004). 

Diarrhea from Salmonella infection is usually self-limiting and does not require treatment unless 

severe. Overall, there is an estimated 22.1 percent hospitalization rate, and an estimated 0.8 

percent fatality rate (USDA, 2005). Mortality from S. typhi and S. paratyphi is estimated to be 

between 10 to 15 percent without treatment (Ohl, 2001). In severe cases, fluid and electrolyte 

replacement may be needed. Antibiotics are not recommended to treat Salmonella infections, 

except where there is evidence of invasion and septicemia, because they do not alleviate the 

symptoms or reduce the duration of the illness (Kanarat, 2004). Antibiotics may even prolong 

excretion of Salmonella in the feces. 

Salmonellosis Incidence 

Foodborne Salmonella are the estimated cause of approximately 1.4 million foodborne-related 

illnesses, 15,600 foodborne illness-related hospitalizations, and 550 foodborne-related deaths 

each year in the United States (Mead et al., 1999). In 2005, 45,322 salmonellosis cases were 

reported to the CDC through the Public Health Laboratory Information System (CDC, 2007a). 

Community surveys during outbreaks suggest that the proportion of infections reported is 

between 1 in 10 and 1 in 100 (Cohen, 1986). 

Between 1991 and 2002, 3 waterborne outbreaks (833 cases) were attributed to nontyphoid 

Salmonella (Craun et al., 2006). Craun et al. (2005) reported that Salmonella were the etiologic 

agent in 0.9 percent of 259 recreational waterborne outbreaks occurring from 1971 to 2000. 

II.1.4 Leptospira 

Leptospira Strain Variation and Zoonotic Potential 

Leptospira is an aerobic, motile spirochaete, 6 to 20 μm long and 0.1 μm wide. Leptospira 

occurs worldwide and has become an important recreational zoonosis due to its prolonged 

survival in water (Pond, 2005). The genotypic classification of Leptospira into two species (L. 

interrogans and L. biflexa) has been replaced by a phenotypic classification system in which 13 

genomospecies are currently defined (L. interrogans, L. noguchii, L. santarosai, L. meyeri, L. 

wolbachiic, L. biflexac, L. fainei, L. borgpetersenii, L. kirschneri, L. weilii, L. inadai, L. parvac, 

and L. alexanderi) (Levett, 2001). Of the 28 serovars, several occur in more than one 
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February 2009 18 

genomospecies. Leptospirosis is probably the most widespread zoonosis in the world (Levett, 

2001; Meites et al., 2004). Zoonotic reservoirs include livestock (pigs and cattle), domestic pets 

(dogs), and wild or feral animals (rats, voles, and mice) (Kanarat, 2004; Levett, 2001). 

Complete genome sequences of L. interrogans serovars Copenhageni and Lai reveal that despite 

overall genetic similarity there are significant structural differences in their genomes 

(Nascimento et al., 2004). Nascimento and colleagues analyzed the genomic sequences to gain 

insight into genes that influence motility, chemotaxis, pathogenicity, and colonization of the 

pathogen. 

Leptospira Route of Exposure 

The source of infection in humans is usually either direct or indirect contact with the urine of an 

infected animal (Levett, 2001; WHO, 2003). Workers in direct contact with animal reservoirs 

are at increased risk (e.g., cattle, pig, and dairy farmers, slaughterhouse workers, and 

veterinarians) (Meites et al., 2004). Recreational exposure from swimming or boating in 

freshwater lakes is also possible (Levett, 2004; Meites et al., 2004). Outbreaks are often 

associated with unusual rainfall events or flooding (Bolin et al., 2004b). 

Leptospira Illness Symptoms 

Leptospirosis was first described by Adolf Weil in 1886; thus, the more serious form of 

leptospirosis is still known as Weil’s disease (WHO, 2003). Leptospirosis is biphasic with a 

week-long acute stage followed by approximately 2 weeks of convalescence (Levett, 2001). 

During the acute stage, antibodies are low and the pathogen is detected mainly in the blood and 

cerebrospinal fluid, whereas the convalescent stage corresponds with the appearance of 

antibodies and the presence of pathogens in the urine (Levett, 2001). 

Anicteric leptospirosis can be mild or acute. The majority of infections are either subclinical or 

mild, and patients usually do not seek medical attention (Levett, 2001). Icteric leptospirosis is a 

much more severe disease than anicteric leptospirosis. Icteric leptospirosis accounts for most of 

the high mortality rate, which ranges between 5 and 15 percent. Between 5 and 10 percent of all 

patients with leptospirosis have the icteric form of the disease (Levett, 2001). 

Symptoms associated with leptospirosis include the following: jaundice, anorexia, headache, 

conjunctival suffusion, chills, vomiting, myalgia, abdominal pain, nausea, cough, hemoptysis, 

hepatomegaly, lymphadenopathy, diarrhea, rash (usually lasting less than 24 hours), and fever, 

which can be biphasic and reoccur after 3 to 4 days of remission (Levett, 2001). 

In some cases, acute infection in pregnancy has been reported to cause abortion and fetal death 

(Levett, 2001). Uveitis (ocular complications) is recognized as a chronic sequela of leptospirosis 

in humans and horses. Chronic visual disturbance lasting 20 years or more has been reported 

(Levett, 2001). In 1994, CDC removed leptospirosis from the notifiable diseases list; however, 

the Hawaii Department of Health still requires reporting (Katz, 2001; Levett, 2001). 
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February 2009 19 

Leptospirosis Incidence 

Levett (2001) summarized information for 28 waterborne outbreaks of leptospirosis worldwide, 

22 of which were associated with swimming, 1 with kayaking, and 1 with rafting. Within the 

United States, the highest incidence of leptospirosis is found in Hawaii (Katz, 2001). Between 

1971 and 2000, 16 percent of recreational waterborne disease outbreaks were attributed to 

Leptospira (Craun et al., 2004a). In 1998, in Illinois, there was an outbreak (375 cases) of 

leptospirosis associated with a triathalon in a lake (CDC, 2000). 

In a prospective, population-based study of patients presenting with acute febrile illness, the 

geographic distribution of human Leptospira isolates mirrored the distribution of Leptospira 16S 

ribosomal gene sequences in urban and rural water sources (Ganoza et al., 2006). 

II.2 Protozoa 

II.2.1 Cryptosporidium 

Cryptosporidium is a small protozoan parasite that infects the microvillous region of epithelial 

cells in the digestive and respiratory tract of humans and other mammals, birds, reptiles, and fish. 

Cryptosporidium does not replicate outside of a host. Environmentally robust oocysts are shed 

by infected hosts into the environment and can survive in environmental conditions for long 

periods of time (up to months) until ingested by a new host. In the new host, the life cycle starts 

again, and multiplication occurs using the biological resources of the host (WHO, 2006). 

Cryptosporidium exists in the natural environment in the oocyst form and which are resistant to 

conventional drinking water treatment measures such as chlorination. Cryptosporidium is 

recognized as a widespread pathogen for the general population, including both 

immunocompromised and immunocompetent persons (WHO, 2006). 

Cryptosporidium Life Cycle and Strain Variation 

Cryptosporidium has a complex life cycle. Each oocyst, which has an environmentally resistant 

wall, holds four sporozoites. Oocysts enter the environment by passing with the feces of an 

infected host organism (Fayer and Ungar, 1986; Fayer et al., 1997). Oocysts are immediately 

infectious and may remain in the environment for very long periods without losing their 

infectivity. Oocysts are resistant to environmental conditions and natural decay and can travel 

passively through the environment until they are ingested by a new host organism. In the GI 

tract of the new host, 4 sporozoites exit each oocyst (excyst) and may form an infection in the 

epithelial cells of the small intestine of the host (USEPA, 2001a). The sporozoites transform 

through several life stages including an asexual and a sexual reproduction cycle. Oocysts are the 

result of the sexual reproduction cycle. Oocysts of the two species of Cryptosporidium

responsible for most human infections—C. hominis and C. parvum—are spherical with a 

diameter of 4 to 6 μm. Thin-walled oocysts may excyst within the same host and start a new life 

cycle (autoinfection), whereas thick-walled oocysts generally are shed by the host. 

Autoinfection may lead to a heavily infected epithelium of the small intestine resulting in 

secretory diarrhea (WHO, 2006). 
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February 2009 20 

Cryptosporidium is part of phylum Apicomplexa, family Cryptosporidiidae, and has been 

classified as a member of the group of eimeriid coccidian—a diverse group of parasitic protozoa 

(WHO, 2006). There are currently 16 species of Cryptosporidium identified in the literature 

(Table II.2.1-1). However, this taxonomy is likely to change as molecular methods continue to 

characterize isolates and potential new species. Fayer (2004a) and Olson et al. (2003) updated 

the list of Cryptosporidium species that have been reported to infect humans to include C. 

baileyi, C. canis, C. felis, C. hominis, C. meleagridis, C. muris, and C. parvum. It is important to 

note that the human form of C. parvum (formerly referred to as H-type or genotype 1) was 

recently reclassified as a new species, C. hominis (Morgan-Ryan et al., 2002). The cattle form of 

C. parvum (formerly referred to as C-type or genotype 2) maintains the designation C. parvum. 

Thus, studies published prior to 2002 should be interpreted carefully keeping in mind that 

authors who refer to C. parvum may be referring to C. parvum, C. hominis, or both. Of the 

current 16 species of Cryptosporidium, C. parvum and C. hominis most commonly cause GI 

illness in humans. 

Studies with volunteers have demonstrated that a low dose of C. parvum (e.g., 10 oocysts) is 

sufficient to cause infection in healthy adults although some strains may be more infectious than 

others (Chappell et al., 1999; DuPont et al., 1995; Okhuysen et al., 2002). The relationship 

Table II.2.1-1. Cryptosporidium Species 

Cryptosporidium Species Initially Described Host Species 

C. andersoni Bos taurus (domestic cattle)

C. baileyi Gallus gallus (domestic chicken)

C. bovis Bos taurus (domestic cattle)

C. canis Canis familiaris (dogs)

C. felis Felis catis (domestic cat)

C. galli Gallus gallus (domestic chicken)

C. hominis Homo sapiens (humans, formerly C. parvum genotype 1)

C. meleagridis Meleagris gallopavo (turkey)

C. molnari Dicentrarchus labrax (fish)

C. muris Mus musculus (house mouse)

C. nasorum Naso lituratus (fish)

C. parvum Mus musculus (house mouse) (formerly genotype 2)

C. scopthalmi Scopthalmi maximus (turbot)

C. serpentis Elaphe guttata (corn snake)

E. subocularis (rat snake)

Sanzinia madagascarensus (Madagascar boa)

C. suis Sus scrofa (pig)

C. varanii Varanus prasinus (emerald monitor lizard)

C. wrairi Cavia porcellus (guinea pig)

Source: Adapted from Cacciò, 2005; Fayer, 2003, 2004a; Fayer et al., 1997, 2000; Fayer and Xiao, 

2007; Morgan-Ryan et al., 2002; Ryan et al., 2003; and Xiao and Ryan, 2004. 
U.S. Environmental Protection Agency

February 2009 21 

between the number of oocysts humans are exposed to and the probability of infection is 

discussed in detail in the subsequent section. Studies of immunosuppressed adult mice have 

demonstrated that a single viable oocyst can induce C. parvum infections (Okhuysen et al., 2002; 

Yang et al., 2000). 

Genetic and molecular studies of C. parvum (including C. hominis) indicate that the species is 

genetically heterogeneous among isolated strains found in different host species (Xiao and Ryan, 

2004). There also is evidence that C. parvum and C. hominis experience recombination and that 

polymorphisms exist in the C. hominis species (Widmer et al., 1998). Okhuysen et al. (1999) 

showed that different isolates of C. parvum (including C. hominis) have different levels of 

infectivity for humans, and therefore the heterogeneity of the species may influence the risk 

posed to public health. Furthermore, distinct transmission cycles are evident among different 

genotypes of C. parvum. Multiple genotypes have been shown to circulate among different host 

species, and mixed infections with genotypically distinct populations have been reported 

(Widmer et al., 1998). 

Cryptosporidium Zoonotic Potential 

Human cases of cryptosporidiosis typically have been associated with different kinds of animal 

contact, which has led to the widespread belief that the host-range of Cryptosporidium is very 

broad and many animals can serve as reservoirs for Cryptosporidium. Cryptosporidium infection 

has been reported in more than 155 mammalian species (Fayer, 2004a) as well as numerous 

reptiles, amphibians, birds, and fish (O’Donoghue, 1995). 

Several lines of evidence indicate that livestock, primarily cattle and sheep, are a major source of 

Cryptosporidium contamination of drinking water sources. These include the detection of C. 

parvum (presumably from animals) in many source waters and elevated levels of 

Cryptosporidium in watersheds with extensive agricultural activity (Fayer, 2004a; WHO, 2006). 

Also, direct zoonotic transmission of Cryptosporidium infection from livestock to humans has 

been repeatedly demonstrated (WHO, 2006). During outbreaks of cryptosporidiosis, frequent 

detection of Cryptosporidium in human stool samples suggests that human sources can also add 

significantly to the occurrence of oocysts in source waters (Fayer, 2004a). 

Based on data from the western United States, depending on climate and feedlot management 

systems, the average animal in a cattle feedlot excretes between 28,000 and 140,000 oocysts per 

day (Atwill et al., 2006). Furthermore, 91 percent of dairy farms studied by Sischo et al. (2000) 

had Cryptosporidium at their locations, with 15 percent of infant dairy calves shedding oocysts. 

Nine percent of farm-associated streams contained C. parvum. Therefore, cattle represent a 

significant reservoir and potential environmental source of C. parvum. Tate et al. (2000) 

demonstrated that oocysts can be carried by runoff during rain events. 

Most outbreaks of cryptosporidiosis are caused by C. hominis, which is only transmitted by 

human hosts. Outbreaks represent only 10 percent of domestic cryptosporidiosis cases, however, 

and at least one study (Feltus et al., 2006) has shown that the zoonotic C. parvum may be 

responsible for the majority of sporadic (endemic) cases. Atwill et al. (1997) reported that feral 
U.S. Environmental Protection Agency

February 2009 22 

pigs may serve as an environmental reservoir for C. parvum and may represent a potential source 

of Cryptosporidium contamination of ambient waters. 

Although it is clear that livestock may be a major contributor to drinking water source 

contamination, there are few data to support a quantitative estimate of the proportion of this 

contribution. Cryptosporidium levels in source water are known to vary seasonally (USEPA, 

2005a, 2005b), and short-term levels in surface water can be strongly associated with storm 

events or other weather variables (Fayer, 2004a; Naumova et al., 2005; USEPA, 2005a; WHO, 

2006). In watersheds with diverse land-use patterns, it is likely that different sources contribute 

different proportions to the total contamination load at different times during the year, with the 

relative contributions depending on a wide range of watershed characteristics. 

Besides animal contamination, the other major source of Cryptosporidium in ambient water is 

human fecal wastes. Several mechanisms can be responsible for the contamination of source 

waters and include malfunctioning septic systems, routine or “upset” releases from municipal 

wastewater treatment facilities, combined sewer system overflows, or human recreational uses 

(e.g., swimming, camping, and hiking). Due to the large numbers of oocysts excreted by 

infected individuals (Okhuysen et al., 1999) and oocyst resistance to many conventional 

wastewater treatment processes, even small releases can be significant. The World Health 

Organization (WHO) found reports of raw sewage samples containing up to 14,000 oocysts/L 

(average was up to 5,300 oocysts/L) and treatment plant effluents containing between 17 and 250 

oocysts/L (WHO, 2006). Clearly, in water bodies where treatment effluents comprise an 

appreciable proportion of total flow, their contribution to the total Cryptosporidium load may be 

substantial. 

LeChevallier et al. (2003) reported the results of Cryptosporidium monitoring for approximately 

600 samples from 6 watersheds located in the United States and Canada. They found that the 

two watersheds with the highest proportion of agricultural land use had the highest average 

Cryptosporidium levels2

 and that approximately 90 percent of the samples exhibited the bovine 

(cattle) genotype (C. parvum). These findings implicate livestock, at least in these watersheds, 

as the major contributor to overall Cryptosporidium levels. This finding is consistent with 

studies indicating that the prevalence of Cryptosporidium infection in young livestock (i.e., 

calves and lambs) is very high (Fayer, 2004a) and that the oocyst counts in feces of young 

infected animals ranges from 106

 to 108 oocysts per gram (WHO, 2006). 

McCuin and Clancy (2006) conducted a 15-month occurrence study of Cryptosporidium

occurrence in 10 wastewater facilities across the United Sates. Indigenous oocysts were detected 

in 30 percent of raw influents, 46 percent of primary effluents, 58 percent of secondary effluents 

and 19 percent of tertiary effluents in the 289 analyzed samples. Zhou et al. (2003) analyzed 179 

wastewater treatment plant effluent samples from Milwaukee, Wisconsin using polymerase chain 

reaction (PCR) restriction fragment length polymorphism (RFLP) methods to characterize 

genotypes of detected Cryptosporidium. In contrast with the results observed for source waters 

by LeChevallier et al. (2003), C. hominis (13.4 percent of samples) was detected more frequently 

than C. parvum (2.8 percent). This finding suggests that the distribution of Cryptosporidium in 

 2

 These results were obtained using EPA Method 1623 (USEPA, 2001b), for which the authors reported an 

average recovery rate of 72±22 percent. 
U.S. Environmental Protection Agency

February 2009 23 

Milwaukee’s population was not heavily influenced by agricultural sources, though the relative 

low levels of C. parvum in wastewater may also have been due to differences in infectivity, 

excretion, or both of this species relative to C. hominis. As is the case for livestock, the extent to 

which human wastes contribute to overall Cryptosporidium contamination is highly site-specific, 

seasonal, and variable. 

Cryptosporidium Route of Exposure 

The main route of exposure to illness-causing microorganisms in recreational waters is through 

accidental ingestion of contaminated water while engaging in full immersion activities such as 

swimming or bathing. Secondary contact or partial body contact recreation such as wading, 

canoeing, motor boating, and fishing, in which ingestion is unlikely due to lack of direct water 

contact with the ears, eyes, mouth, or nose, is not considered to result in significant exposure 

(USEPA, 2002). A recent pilot study of anglers in the Baltimore area by Roberts et al. (2007), 

however, suggested that between 1 and 8 of 10 urban anglers could become infected with 

Cryptosporidium. This small study (56 anglers; a total of 46 fish/hand wash samples) included 

quantitative risk modeling. No data were reported on microbial water quality at the sampling 

sites, nor was there any attempt to obtain either health effects data or clinical samples to evaluate 

infection rates in the study population. 

The potential for person-to-person secondary transmission is high for Cryptosporidium 

infections. Based on an analysis of data from the 1993 Milwaukee outbreak, Eisenberg et al. 

(2005) suggested that 10 percent (95 percent confidence interval: 6 to 21 percent) of the cases of 

disease were due to person-to-person transmission. There is considerable evidence that direct 

person-to-person transmission, as well as indirect transmission through contact with 

contaminated objects, can be a significant route of infection, especially where human population 

densities are high or personal contact is frequent (USEPA, 2001a). Direct transmission is 

affected by behavioral factors (e.g., frequent travel) and ethnic and dietary differences (USEPA, 

2001a). Using data from the Milwaukee outbreak, approximately 3 to 5 percent of infected 

individuals transmit the disease to others (Mackenzie et al., 1995; Osewe et al., 1996). Among 

children and their caretakers, however, the transmission rate is considerably higher (12 to 22 

percent) (Osewe et al., 1996). 

Cryptosporidium Illness Symptoms 

Cryptosporidiosis is primarily characterized by GI symptoms such as profuse watery diarrhea; 

however, diarrheal symptoms are generally not distinguishable from those caused by other 

common enteric pathogens. Other symptoms reported by individuals afflicted with 

cryptosporidiosis include dehydration, fever, anorexia, weight loss, weakness, abdominal 

cramps, vomiting, lethargy, general malaise, and progressive loss of overall condition (Hunter et 

al., 2004). The incubation period (time from ingestion to appearance of symptoms) has been 

reported to range from 2 to 10 days (Arrowood, 1997). 

Some infections may be asymptomatic. In other words, not all infections will result in illness 

and observable symptoms. Asymptomatic hosts may still shed oocysts, however. Asymptomatic 

carriage, as determined by stool surveys, generally occurs at very low rates (less than 1 percent) 
U.S. Environmental Protection Agency

February 2009 24 

in industrialized countries (Current and Garcia, 1991), though higher rates have been reported in 

day care centers. Routine bile endoscopy suggests a higher asymptomatic prevalence; for 

example, 13 percent of nondiarrheic patients were shown to carry Cryptosporidium oocysts 

(Roberts et al., 1989). High rates of asymptomatic infection (between 10 and 30 percent) are 

common in nonindustrialized countries (Current and Garcia, 1991). 

In more severe illnesses, the parasite may be found in the stomach, colon, liver, or lungs with 

associated symptoms corresponding to infections in those tissues. However, the presence of the 

parasite in tissues other than the small intestine does not necessarily indicate infection of host 

cells in those organs (O’Donoghue, 1995). 

The level of immunocompetence of the infected person directly relates to the symptoms 

experienced. Age, concurrent illness/medical treatment, genetic background, pregnancy, and 

nutritional status all contribute to immune status. Symptoms may be more severe in 

immunocompromised persons (Carey et al., 2004; Frisby et al., 1997). Such persons include 

those with AIDS, certain cancer patients undergoing chemotherapy, organ transplant recipients 

treated with drugs that suppress the immune system, and patients with autoimmune disorders 

(e.g., lupus). In AIDS patients, Cryptosporidium has been found in the lungs, ears, stomach, bile 

duct, and pancreas in addition to the small intestine (Farthing, 2000). Clifford et al. (1990) found 

that cryptosporidiosis affected 10 to 15 percent of the AIDS patients, resulting in death in 50 

percent of those cases. Besides the immunocompromised, children and the elderly may also be 

at higher risk from Cryptosporidium than the general population; however, specific data are not 

currently available to document the degree to which these individuals are subject to elevated risk. 

However, previous exposure to Cryptosporidium has been shown to confer some amount of 

immunity (Chappell et al., 1999). 

Symptoms of cryptosporidiosis typically last from several days to 2 weeks although, in a small 

percentage of cases, the symptoms may persist for months or longer. Individuals with either 

compromised or healthy immune systems may experience illness for long periods. Illness from 

Cryptosporidium is usually self-limiting, with a median duration of 6 days and a mean duration 

of 9 days (Dupont et al., 1995; Palmer et al., 1990), although longer durations (mean 19 to 22 

days, maximum 100 to 120 days) were reported in a recent Australian survey by Robertson et al.

(2002). Relapses were common, with 1 to 5 additional episodes in 40 to 70 percent of patients. 

Shedding of oocysts may continue after the cessation of the disease symptoms. 

Both individuals with compromised and with healthy immune systems have been shown to 

exhibit chronic sequelae. Immunocompromised individuals generally experience chronic 

gastroenteritis, which may last as long as the immune impairment. Immunocompromised 

populations include patients undergoing chemotherapy for treatment of neoplasms, persons 

undergoing immune suppression treatment to prevent rejection of skin or organ transplants, 

malnourished individuals, persons with concurrent infectious diseases (e.g., measles), the elderly, 

and persons with AIDS. Chronic illness may manifest itself as a series of intermittent episodes 

or may be persistent. Individuals with CD4+ cell counts (a key measure of the health of the 

immune system) less than 100 cells per mm3

 of blood are at increased risk of illness from 

Cryptosporidium, while individuals with less than 50 cells per mm3

 are at the greatest risk for 
U.S. Environmental Protection Agency

February 2009 25 

severe disease and prolonged carriage of Cryptosporidium (Hunter and Nichols, 2002; Roefer et 

al., 1996). 

As noted above, chronic sequelae in immunocompetent patients also have been documented. 

After resolution of the acute phase in the 2 months following their initial diagnosis, 40.9 percent 

of patients in one case study reported recurrence of intestinal symptoms (includes both C. 

hominis and C. parvum) (Hunter et al., 2004). In addition, in individuals infected with C. 

hominis, other sequelae such as joint pain, eye pain, recurrent headache, dizzy spells, and fatigue 

were significantly more common than in control subjects. Both C. parvum and C. hominis

infections have sometimes resulted in recurrence of GI symptoms, but only C. hominis infections 

have been related to the other sequelae noted previously. 

Cryptosporidiosis Incidence 

Limited information is available on the endemic incidence of cryptosporidiosis in the United 

States. Mead et al. (1999) estimated that there are approximately 15 million physician visits 

annually for diarrhea and that approximately 2 percent of these, or 300,000 cases, are due to 

cryptosporidiosis. Mead and colleagues also estimated that of these 300,000 cases, only about 

10 percent are attributable to foodborne transmission, with the remainder due to the consumption 

of contaminated water (from drinking or recreational exposure) or person-to-person contact. 

Mead et al. (1999) estimated that there are approximately 211 million episodes of gastroenteritis 

(GI illness) in the United States each year, of which only about 38 million are attributable to 

known pathogens.3

Prior to 1982, when the CDC implemented routine reporting of Cryptosporidium among AIDS 

patients, only 13 cases of cryptosporidiosis had been documented (Ungar, 1990). Subsequently, 

between 1982 and 1997, more than 1,000 cases of the disease were reported worldwide (Fayer et 

al., 1997). Cases reported by CDC between 1999 and 2005 (for all routes of exposure) are 

shown in Figure II.2.2-1; however, documented cases underestimate actual Cryptosporidium 

infection rates because most cases go unreported. 

Worldwide, infection is widespread, exceeding several million according to Casemore et al. 

(1997). As noted previously, the largest known outbreak of the disease occurred in 1993 in 

Milwaukee, Wisconsin (MacKenzie et al., 1994) and infected 403,000 individuals (CDC, 1996). 

The most recent data from CDC (2007b) for the year 2005 reported 8,269 cases of 

Cryptosporidium infection nationally, and reported significant fluctuations in incidence between 

summer and other seasons, peaking in late July and early August. According to CDC (2007b), 

Cryptosporidium is the leading cause of diarrheal illness outbreaks in recreational (chlorinated 

and nonchlorinated) water. Although 8,269 cases were reported in the United States in 2005, 

CDC (2007b) estimates that the total incidence of domestic cases of Cryptosporidium infection 

exceeds 300,000 each year. 

 3

 Mead et al. (1999) based the estimates on reported cases and estimates for degree of under reporting. For 

example, in the 1993 cryptosporidiosis outbreak in Milwaukee, Wisconsin, medical care was sought in only 12 

percent of cases (Corso et al., 2003). 
U.S. Environmental Protection Agency

February 2009 26 

Figure II.2.1-1. Reported Cryptosporidium Infections in the United States, 1999 to 2005 

 

The large increase in the number of cases reported from 2003 to 2005 might have resulted from 

outbreak-related case reporting (CDC, 2007b); however, that factor is unlikely to account for all 

of the increase. It is not clear how much, if any, of the increase may be due to changes in 

reporting patterns and diagnostic testing practices or to a real change in infection and disease 

(CDC, 2007b). 

From 1991 to 2004, six outbreaks of cryptosporidiosis have been associated with untreated 

recreational waters (Table II.2.1-2). 

II.2.2 Giardia

Giardia Life Cycle and Strain Variation 

Organisms in the genus Giardia are binucleate, flagellated protozoan parasites that exist in 

trophozoite and cyst forms and are an important cause of waterborne illness worldwide. Both 

humans and some animal species can carry and transmit Giardia lamblia (also known as G. 

intestinalis or G. duodenalis), which causes the GI illness giardiasis. G. lamblia is highly 

infectious and has been shown to cause giardiasis with exposure to as few as 10 cysts (Rendtorff, 

1954). 

Over the course of the Giardia life cycle, the parasite lives both as a trophozoite and as a cyst 

form. Inside a vertebrate host, the Giardia trophozoites divide by binary fission, attach to the 

brush border of the small intestinal epithelium, detach, then become rounded and form a cyst 

wall. The environmentally resistant cyst is excreted with the feces, where it moves passively 

Cryptosporidium Cases in the United States 

9,000 1999-2005

8,000

ses

7,000

am C6,000 iu

5,000

idro4,000 psot3,000 pyr2,000 C

1,000

0

1999 2000 2001 2002 2003 2004 2005

Year

Data sources: CDC 2005, 2007
U.S. Environmental Protection Agency

February 2009 27 

Table II.2.1-2. Outbreaks of Cryptosporidiosis Associated with Recreational Waters in the 

United States 

Year Number of Cases Number of Outbreaks Source of Outbreak(s) 

1991 0 0 NA 

1992 526 2 Waterslide and wave pool

1993 174 4 Pools 

1994 519 2 1 pool, 1 lake

1995 5,487 3 1 pool, 2 waterparks 

1996 3,025 3 2 pools, 1 lake 

1997 369 1 Fountain

1998 169 8 7 pools, 1 lake 

1999 64 4 3 pools, 1 fountain

2000 1,368 13 12 pools, 1 lake

2001 538 4 3 pools, 1 hot spring

2002 936 7 6 pools, 1 lake 

2003 702 5 4 pools,* 1 lake

2004 567 7 Pools 

* In one pool outbreak, both Cryptosporidium and Giardia were detected in water samples, so that 

outbreak of 63 cases is counted in both the Cryptosporidium and the Giardia data. 

Source: Data from CDC Surveillance Summaries: Morbidity and Mortality Weekly Report (MMWR) 

Surveillance for Waterborne-Disease Outbreaks - United States: 1991-1992, 1993-1994, 

1995-1996, 1997-1998, 1999-2000, 2001-2002, 2003-2004 (CDC, 1993b, 1996, 1998, 

2000, 2002, 2004, 2006).

through the environment and may be ingested by another host organism. Inside the digestive 

track of a new host, active cysts release trophozoites, and repeat their lifecycle (USEPA, 1998). 

Cysts can be excreted in the stool intermittently for weeks or months, resulting in a protracted 

period of communicability (CDC, 2007b). Furthermore, cysts can remain viable under typical 

environmental conditions for periods up to 77 days (Bingham et al., 1979, as cited in USEPA, 

1998). 

Currently, there are five recognized species of Giardia and six generally recognized assemblages 

of G. lamblia. Each assemblage has a varying degree of host specificity (see Table II.2.2-1). 

Some assemblages (i.e., Assemblages A and B) act as zoonotic assemblages that can infect most 

species of mammal, while others (i.e., Assemblages C through F) are more adapted to a 

particular host species (Appelbee et al., 2005). For example, Assemblage A has been found in 

human, beaver, cat, lemur, sheep, calf, dog, fox, chinchilla, alpaca, horse, pig, and cow. The role 

of these animals as a source of human infection, however, remains unclear. Assemblages C and 

D seem to primarily infect dogs, while Assemblage E infects livestock, and Assemblage F infects 

only cats (Appelbee et al., 2005). 
U.S. Environmental Protection Agency

February 2009 28 

Table II.2.2-1. Giardia Taxonomy 

Species Assemblage Host(s) 

Giardia lamblia 

(syn. G. duodenalis, 

G. intestinalis) 

A1 Human, beaver, cat, lemur, sheep, calf, dog, fox, chinchilla, 

alpaca, horse, pig, cow 

G. lamblia A2 Human, beaver 

G. lamblia B (G. enterica*) Human, beaver, guinea pig, dog, monkey, horse

(B IV) 

G. lamblia C and D 

(G. canis*) 

Dog, coyote, mouse

G. lamblia E (G. bovis*) Cow, sheep, alpaca, goat, pig

G. lamblia F (G. cati*) Cat

G. lamblia G (G. simoni*) Domestic rat 

G. lamblia Novel I Marsupial (Quenda – bandicoot, mouse, sheep) 

G. lamblia Novel II Marsupial II (Tasmanian devil) 

G. muris Rodents (mice) 

G. microti Vole and muskrat

G. psittaci Birds (budgerigars) 

G. ardeae Birds (heron and ibis) 

G. agilis Amphibians (frogs) 

* Denotes recently proposed new species names (Hunter and Thompson, 2005; Thompson and Monis,

2004). 

Adapted from: Adam, 2001; Appelbee et al., 2005; Hamnes et al., 2007; Olson et al., 2004; and Traub et

al., 2005. 

Giardia Zoonotic Potential 

Cross-species transmission of Giardia is known to occur, and there are many known species and 

variants (or assemblages) of the Giardia parasite. Of all of the animal host species suspected of 

being a significant zoonotic source of human giardiasis by waterborne transmission, the evidence 

presently available suggests that the beaver (Dykes et al., 1980) and muskrat (USEPA, 1998) are 

the most likely candidates. The role of these animals as a source of human infection, however, 

remains controversial. Both of these aquatic mammals can be infected with isolates of Giardia

from humans, but each has also been shown to harbor strains of Giardia that are phenotypically 

distinct from those found in humans. Thus, it is possible that the beaver harbors two types of 

Giardia. One type may be highly adapted to this animal and rarely, if ever, transmitted to 

humans. The other type may be one acquired by the beaver from human sources, which can 

multiply in the beaver and in turn be transmitted via water back to humans (USEPA, 1998). 

The role that livestock play as zoonotic reservoirs of Giardia infection also remains 

controversial. G. lamblia may be maintained independently through transmission cycles 

involving wildlife and livestock, though it is unclear how these cycles may interact in zoonotic 

transfer (Hunter and Thompson, 2005). While both livestock and humans have been implicated 
U.S. Environmental Protection Agency

February 2009 29 

in contaminating water sources with Giardia, humans are responsible for the majority of the 

contaminations. Hunter and Thompson (2005) examined case studies for the zoonotic potential 

of Giardia and found only one case having a significant association with animal contact. They 

concluded that zoonotic transfer plays only a minor role in the infection cycles of Giardia and 

that animal contact is not a major risk factor. They authors did not, however, rule out the 

importance of zoonotic transfer indirectly through water sources. Both Traub et al. (2004) and 

Inpankaew (2007) have shown that, in some communities with inadequate sanitation, zoonotic 

transfer is evident between humans and dogs; however, it is unclear which species is the primary 

reservoir. 

Thompson (2007) suggested that data gaps regarding zoonotic transfer for Giardia can be filled 

using molecular epidemiological studies. Molecular genotyping of parasite isolates from 

susceptible hosts in localized foci of transmission or longitudinal surveillance with genotyping 

might help address such data gaps on zoonotic transfer of Giardia. 

Giardia Routes of Exposure 

Giardia is transmitted via fecal-oral exposure and causes both endemic and epidemic cases of 

giardiasis. It is frequently spread person-to-person, especially among children or among persons 

with poor access to or practice of sanitation. The main route of exposure to Giardia from 

recreational immersion in water is from incidental ingestion of water during full immersion 

activities such as swimming. 

Although inhalation of aerosolized water that contains cysts is theoretically possible, cysts are 

not known to be infectious in lung tissue. Dermal absorption is not known to be a route of 

exposure to Giardia cysts in environmental waters. 

Giardia Illness Symptoms 

Giardia is responsible for a number of health effects including acute symptoms that occur during 

and after the infection. However, Giardia has also been implicated in a number of chronic 

sequelae. There are a wide variety of symptoms associated with giardiasis that range from 

asymptomatic infection and acute self-limiting diarrhea to persistent chronic diarrhea, which 

sometimes fails to respond to treatment. 

Giardia produces a broad spectrum of GI symptoms including one or more of the following 

symptoms: diarrhea, bloating, weight loss, malabsorption, steatorrhea (fatty stool), pale greasy 

and malodorous stools, flatulence, abdominal cramps, nausea and vomiting, fatigue, anorexia, 

and chills (CDC, 2000; Hellard et al., 2000; Hopkins and Juranek, 1991; Thompson, 2000). 

Fever may occur at the beginning of the infection (Ortega and Adam, 1997). Lactose intolerance 

is frequently present during infection and may persist even after Giardia has cleared from the 

stool (Wolfe, 1992). Chronic giardiasis appears to be infrequent, but when it occurs, may persist 

for years (USEPA, 1998). Case reports also indicate that giardiasis can be associated with the 

development of reactive arthritis (Tupchong et al., 1999). 

Illness durations vary, lasting only 3 to 4 days for some individuals and several months for 

others. Most infections resolve spontaneously, and the acute stage lasts from 1 to 4 weeks 
U.S. Environmental Protection Agency

February 2009 30 

(USEPA, 1998), but individuals with compromised immune systems may have more serious and 

prolonged infection (APHA, 2004). Immunodeficiency with varying degrees of 

hypogammaglobulinemia or agammaglobulinemia is the most commonly reported form of 

immunodeficiency associated with chronic giardiasis (Farthing, 1996). However, giardiasis is 

one of the few potentially treatable causes of diarrhea in persons with AIDS, and chronic 

giardiasis does not appear to be a major clinical problem in persons with HIV infections or AIDS 

(Farthing, 1996; USEPA, 1999). 

Asymptomatic infection is very common, with 50 to 75 percent of infected persons reporting no 

symptoms (Mintz, 1993)—especially in children and in persons with prior infections (CDC, 

2007b). In a study at the Swiss Tropical Institute, only 27 percent of 158 patients who had 

Giardia cysts in their feces exhibited symptoms (Degremont et al., 1981). Although persons 

with asymptomatic Giardia infection are not likely to seek medical treatment and be diagnosed, 

they can serve as carriers of infection. 

 

Hospitalizations and deaths due to giardiasis are relatively rare. The CDC estimates that 

giardiasis causes approximately 10 deaths and 5,000 hospitalizations annually in the United 

States (Mead et al., 1999). Blood volume depletion or dehydration is the most frequently listed 

codiagnosis on hospital admission. Among children under 5 years of age who had severe 

giardiasis, almost 19 percent also were diagnosed with failure to thrive (Lengerich et al., 1994). 

Additionally, in the United States and Scotland, more severe cases of giardiasis (i.e., hospitalized 

patients) seem to occur primarily in children under the age of 5 (Lengerich et al., 1994; 

Robertson, 1996). Age has been shown to significantly affect recovery time; in Scotland, the 

median length of stay in the hospital for giardiasis was significantly longer for persons older than 

70 years than for other age groups (11 days compared to 3 days) (Robertson, 1996). Infants and 

young children may have increased susceptibility to giardiasis due to immunological factors that 

increase sensitivity and behavioral factors that increase exposure. 

Chronic giardiasis patients often experience recurrent, persistent, brief episodes of loose, foul 

smelling stools that may be yellowish and frothy in appearance and frequently accompanied by 

distension of the bowel, foul flatus, anorexia, nausea, and uneasiness in the epigastrium (Wolfe, 

1979). In some cases, these symptoms may persist for years; however, in the majority of cases, 

the parasite and symptoms disappear spontaneously. Among 65 cases of giardiasis encountered 

in an urban private practice outpatient setting, the mean duration of symptoms was reported to be 

1.9 years, and in 38 patients (58 percent) who exhibited chronic symptoms for 6 months or 

longer, the mean duration of symptoms was 3.3 years (USEPA, 1998). 

Corsi et al. (1998) evaluated ocular manifestations in 141 Italian children with current and past 

giardiasis and 300 children without giardiasis. Retinal changes were diagnosed in 20 percent of 

the children with giardiasis (mean age was 4.7 years) and in none of the children without 

giardiasis. These findings suggest that asymptomatic, nonprogressive retinal lesions may occur 

in young children with giardiasis. The risk of retinal lesions did not seem to be related to the 

severity of infection, its duration, or use of metronidazole to treat the infection, and may reflect a 

genetic predisposition to retinal lesions (Corsi et al., 1998). 
U.S. Environmental Protection Agency

February 2009 31 

There is usually no extra-intestinal invasion when Giardia trophozoites infect the small intestine, 

but reactive arthritis may occur, and in severe giardiasis, duodenum and jejunal mucosal cells 

may be damaged (APHA, 2004). 

Giardiasis Incidence 

Giardia lamblia is the most common intestinal parasite identified by public health laboratories in 

the United States (Kappus et al., 1994; Rose et al., 1991). CDC estimates that there are 

approximately 2 million illnesses annually in the United States due to Giardia (Mead et al., 

1999). As noted previously, while all age groups are affected by giardiasis, the highest incidence 

is in children (USEPA, 1998). High risk groups for giardiasis include infants and young 

children, travelers to developing countries, the immunocompromised, and persons who consume 

untreated water from lakes, streams, and shallow wells (USEPA, 1998). 

Communities with unfiltered surface water systems experienced a waterborne outbreak rate that 

was 8 times greater than communities where surface water was both filtered and disinfected 

(USEPA, 1998). Data therefore indicate that filtering water to remove microorganisms 

substantially reduces risk of giardiasis. 

As with all pathogens, underreporting limits estimates of the true incidence of giardiasis. The 

ratio of reported cases of giardiasis to actual cases is not known. Mead et al. (1999) used a 38-

fold multiplier to estimate incidence for nonbloody diarrhea outcomes (based on Salmonella

data) and a 20-fold multiplier for bloody diarrhea outcomes (based on E. coli data). Applying 

the 38-fold multiplier to the 20,075 giardiasis cases that were reported in 2005 (CDC, 2007b) 

results in an estimated incidence of approximately 762,800 total cases in 2005. However, 

broader estimates are also supported. For example, an estimated 1 to 5 percent of cases of 

salmonellosis are reported to CDC through passive surveillance (Chalker and Blaser, 1988). If 

the 1 to 5 percent reported cases is applied to the giardiasis data, then the giardiasis disease 

burden in the United States in 2006 could have been 401,500 to 2,007,500 cases (135.4 to 677.0 

cases per 100,000 population).4

 The true burden of giardiasis in the United States is likely to fall 

between these two estimates (CDC, 2007b). 

Using data from 1992 to 1997, the number of states reporting occurrence of giardiasis increased 

from 23 to 43, while the annual count of giardiasis cases rose from 12,793 to 27,778, nationally 

(CDC, 2000). Between 1996 and 2001, however, the number of reported cases of Giardia

infection in the United States (50 states plus Washington, DC) decreased gradually from 27,778 

to 19,659 (CDC, 2007b). The cause of this decrease is unknown. Giardiasis became a nationally 

notifiable disease in 2002, and the number of cases increased from 2001 to 2002, then stabilized, 

averaging approximately 20,200 cases per year (CDC, 2007b). See Figure II.2.2-1 and Table 

II.2.2-2 for reported cases of Giardia infection in the United States from 1992 to 2005. 

 4

 Based on U.S. Census data for 2006, the U.S. population was estimated to be 296,528,800. 
U.S. Environmental Protection Agency

February 2009 32 

Figure II.2.2-1. Reported Giardia Cases in the 50 States plus Washington DC, 1992 to 2005 

The increase in Giardia cases observed for 2002 might reflect increased reporting after the 

designation of giardiasis as a nationally notifiable disease starting in 2002. Outbreak-related 

cases made up 1.6 to 11.6 percent of the total number of cases reported annually for 1999 to 

2002. Although the number of states reporting cases increased from 42 to 46 during that time, 

the number of states reporting more than 15 cases per 100,000 population decreased from 10 in 

1998 to 5 in 2002. Transmission of giardiasis occurs throughout the United States, with 

increased diagnosis or reporting of cases per 100,000 population occurring in northern states than 

Table II.2.2-2. Giardia Infection Occurrence in U.S. Populations 

Population 

Description Occurrence Reference(s)

General 2-5% infection USEPA, 1998 

Prevalence in stool samples (infection) 4-12% depending 

on year and state 

USEPA, 1998 

30% of the population has seropositivity for Giardia

(indicates current or past infection) 

Frost and Craun, 1998

In national survey, 7.2% (of 216,675) stool specimens USEPA, 1999 

were positive for Giardia in 1987 and 5.6 percent (of 

178,786) were positive in 1991 (infection) 

Homosexual males 18% found positive for Giardia (infection) (compared with Faubert et al., 2000; 

(in New York) 2% among other patients, but giardiasis is not a major 

clinical problem in persons with HIV or AIDS) 

Kean, 1979; USEPA, 

1999 

Small children 7% are asymptomatically infected with Giardia Frost and Craun, 1998

Giardia Cases in the United States 1992-2005

30,000

)C Ds25,000 ul pse20,000 att50 S 15,000 (sesa10,000 a Cid

5,000

ariG

0

1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005

Year

Data sources: CDC 2000, 2005, 2007
U.S. Environmental Protection Agency

February 2009 33 

in southern states (CDC, 2005). For 2002, among states reporting cases, the incidence of 

giardiasis ranged from less than 0.1 cases (Texas) to 23.5 cases (Vermont) per 100,000 

population. Vermont reported the greatest number of cases per 100,000 population for each of 

the 5 years of the reporting period. 

Giardiasis occurs most frequently in the early summer through early fall, with increases in 

transmission during the summer (CDC, 2007b). This increased transmission coincides with the 

summer recreation season, which includes increased use of recreational (including community) 

swimming facilities. Given that a single person can shed millions of cysts and yet remain 

asymptomatic, transmission in these facilities is likely to be an important mechanism for 

increased incidence during the summertime (CDC, 2005). People at recreational beaches have 

been shown to disturb sediment, leading to resuspension of cysts and an increase in exposure to 

Giardia, with higher densities of bathers leading to higher turbidity and correspondingly higher 

cyst concentrations (Graczyk et al., 2007; Sunderland et al., 2007). 

Giardiasis is found most frequently in children 9 years old and younger and in adults aged 35 to 

44 years. These groups correspond to young children and their caretakers, who are at increased 

risk of infection (CDC, 2007b). In 2005, 54.3 percent of reported cases occurred in males 

compared to only 43.9 percent in females, while 1.8 percent of reports did not record gender 

(CDC, 2007b). According to CDC (2007b), the discrepancy between cases in males versus 

females might be attributable in part to increased risk of infection during sexual contact between 

men although the discrepancy was found in nearly every age group. 

A review of the data presented in Table II.2.2-2 clearly indicates that Giardia infection in the 

United States is common and widespread. 

From 1991 to 2004, seven outbreaks of giardiasis have been associated with untreated 

recreational waters (Table II.2.2-3). 

II.3 Viruses Zoonotic Potential 

A great deal of public and animal health policy is based on the premise of the host specificity of 

viruses. That is, it has long been assumed that each virus has a distinct and limited range of host 

species that it can infect.5

 Viruses also are restricted to particular tissues of the host’s body that 

they can infect (i.e., tropism), which affects both the mode of transmission and the disease that 

the virus infection may cause (Cliver and Moe, 2004). Most waterborne viruses are thought to 

be transmitted by a fecal-oral route (i.e., the virus is shed via the intestines and infects upon 

ingestion) that requires a tropism that includes the lining of the GI tract. Viruses that infect via 

the intestine and cause GI illness (e.g., enteroviruses) may also have secondary tropisms in other 

 5

 In this case, a distinction is being made between the important and much studied hypothesis that viral 

evolution accelerates when viruses “jump species” in the case of emerging diseases and the regular maintenance of 

multi-host adaptation that is recognized in other pathogens. Although rapid viral evolution facilitated by crossspecies transmission is a recognized public health concern for viruses that have airborne transmission (e.g. influenza 

and severe acute respiratory syndrome [SARS]-associated coronavirus), cross-species transmission has not been a 

traditional concern for waterborne, fecally transmitted viruses. 
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February 2009 34 

Table II.2.2-3. Outbreaks of Giardiasis Associated with Recreational Waters in the United 

States 

Year Number of Cases Number of Outbreaks Source of Outbreak(s) 

1991 34 4 3 pools, 1 lake 

1992 0 0 NA 

1993 61 3 2 lakes, 1 river 

1994 80 1 Pool 

1995 0 0 NA 

1996 77 1 Pool 

1997 0 0 NA 

1998 0 0 NA 

1999 18 1 Pond 

2000 0 0 NA 

2001 0 0 NA 

2002 2 1 River 

2003 212 2 Pools* 

2004 9 1 Lake 

* In one pool outbreak both Cryptosporidium and Giardia were detected in water samples, so that 

outbreak of 63 cases is counted in both the Cryptosporidium and the Giardia data. 

Source: Data from CDC Surveillance Summaries: Morbidity and Mortality Weekly Report (MMWR)

Surveillance for Waterborne-Disease Outbreaks - United States: 1991-1992, 1993-1994,

1995-1996, 1997-1998, 1999-2000, 2001-2002, 2003-2004 (CDC, 1993b, 1996, 1998, 2000,

2002, 2004, 2006). 

tissues (e.g., neurological tissues). While much virus infectivity research has been conducted in 

vitro using cultured animal cells that at least partially reflect the host specificity (but not the 

tropisms) of viruses, many important enteric waterborne viruses of humans (e.g., noroviruses) 

remain difficult to detect or quantify in cultured cells (NRC, 2004; Straub et al., 2007). For this 

reason, it remains unclear whether in vitro infectivity is relevant to the in vivo host ranges of 

viruses. Although no confirmed examples of waterborne viral zoonoses have been reported, 

several viruses (e.g., swine hepatitis E virus [HEV]) are potentially transmissible between 

species, and water may serve as a vehicle for their transmission under some circumstances. 

Thus, assessment of the prospect of waterborne viral zoonoses is ongoing (Cliver and Moe, 

2004). 

Cliver and Moe (2004) consider the criteria for determining whether a virus can function as a 

waterborne zoonosis to include the following: 

1. Animal reservoir: Does the agent regularly infect at least one animal species, 

independent of exposure to humans? 

2. Transmission to humans: Are humans who are in contact with the alleged animal 

reservoir more frequently infected with this virus than people who are not? 
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February 2009 35 

3. Shedding: Is the candidate virus shed by the reservoir animal species in ways that might 

lead to contamination of water? 

4. Stability: Is the candidate virus stable enough in the water vehicle to permit transmission 

by this pathway? 

Despite the potential for rapid evolution in viruses, ongoing monitoring and research activities 

are important for public health protection, even though viruses are not currently known to have 

the attributes outlined in the introduction of this paper. An overview of information related to 

zoonotic potential for rotavirus, HEV, and adenovirus follows. 

Rotaviruses 

Rotaviruses (groups A, B, and C) have been documented in humans and animals, and 

interspecies transmission including human infection by a bovine strain has been reported 

(Abbaszadegan, 2006). The primary route of exposure for rotavirus is the fecal-oral route 

although exposure through other routes also has been reported to a lesser extent. Rotavirus is 

stable in the environment, and its transmission can occur through ingestion of contaminated 

water or food. Rotavirus illness typically results in vomiting and watery diarrhea for 3 to 8 days. 

Fever and abdominal pain occur frequently as well. According to the CDC, this virus is the most 

common cause of severe diarrhea in children. Symptoms tend to be less severe for adults. 

Approximately 70,000 children in the United States are treated in the hospital for rotavirus each 

year (Glass, 2006). A community waterborne outbreak of rotavirus gastroenteritis occurred in 

Colorado in 1981 (Hopkins et al., 1984). The outbreak was attributed to sewage contamination 

of the water supply and a failure of chlorination treatment. 

Hepatitis E 

HEV may be zoonotic (Cliver and Moe, 2004; USEPA, 1999). In pigs and rats, this virus is very 

similar to human HEV. Experimental studies have indicated that human strains can infect pigs, 

and porcine strains can infect primates (Cliver and Moe, 2004). In developing countries, the 

seroprevalence of HEV infection can be as high as 60 percent. The most common route of 

exposure for HEV is ingestion of contaminated food or water. Transmission via person-to-person 

contact is less common. Typical symptoms of HEV illness may include jaundice, fatigue, 

abdominal pain, loss of appetite, nausea, and vomiting. Pregnant women who contract hepatitis 

E are at high risk of severe illness and death. For this sensitive subpopulation, mortality can be 

as high as 20 percent in developing countries, but mortality is rare in developed countries (Craun 

et al., 2004a). HEV is uncommon in the United States and the CDC does not track incidence 

rates. In an EPA study of sporadic human HEV, nearly 50 percent of the infected persons had 

traveled to endemic areas in other countries or received blood transfusions (USEPA, 1999). 
U.S. Environmental Protection Agency

February 2009 36 

Adenovirus 

Adenovirus may be zoonotic (Mwenda et al., 2005). Mwenda and colleagues identified enteric 

adenovirus in captive olive baboons, vervet monkeys, and the yellow baboons in Kenya. These 

findings suggest there may be a possibility of zoonotic transmission of adenoviruses from 

nonhuman primates to humans in Kenya. Adenovirus can enter a susceptible host by the nose, 

mouth, or eye membranes. Water may play a meaningful role in the transmission for many 

human adenovirus serotypes, including the enteric adenovirus that is transmitted via the fecaloral route (Heerden et al., 2005). Heerden et al. (2005) detected human adenovirus in 4 of 51 

(7.8 percent) samples of river water and 9 of 51 (17.7 percent) samples of dam water. 

Human adenoviruses may cause of a wide spectrum of acute and chronic diseases, including 

keratoconjunctivitis, upper respiratory tract infections, pneumonia, gastroenteritis, cystitis, and 

encephalitis (Gray et al., 2005). Molecular studies have recently shown adenoviruses to be 

associated with bronchopulmonary dysplasia (Couroucli et al., 2000) and chronic obstructive 

pulmonary disease (Hogg, 2001). 

Immunocompromised persons, including people with AIDS, bone marrow transplant patients, 

pregnant women, and children are more susceptible to adenovirus infections (Baldwin et al., 

2000; Crawford-Miksza and Schnurr, 1996). Infections in these populations may result in severe 

illness and death (Chakrabarti et al., 2002; Runde et al., 2001). U.S. surveillance for adenovirus 

is relatively incomplete (Gray et al., 2005) and well-documented incidence rates are not 

available, especially for waterborne outbreaks. 
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February 2009 37 

III. PATHOGEN INTERACTIONS WITH THEIR ENVIRONMENT

Pathogens interact with the ambient environment, other microorganisms, plants, and with their 

hosts. This section provides a summary of how pathogens respond to various environmental 

parameters. Information on interactions with other microorganisms and animal manure are 

briefly covered in this overview followed by sections that describe how the water environment 

affects pathogen survivability and phenotype and how host animals can influence pathogen 

characteristics and mechanisms of rapid evolution. The behavior of pathogens in ambient waters 

is often different from the behavior of indicators in ambient water. 

Although there are important waterborne amoebic pathogens, they are not associated with animal 

fecal material. However, important bacterial pathogens that are associated with fecal material 

(e.g., Salmonella, Campylobacter) interact with free-living amoebae in ways that could impact 

recreational water quality. The most notable, Legionella, infects and replicates in free-living 

amoebae and is considered more of a risk in drinking water than in recreational waters (Borella 

et al., 2004; Marrie et al., 2001). Some human bacterial pathogens are even thought to have 

evolved in association with amoebae (Berk et al., 2006). Tezcan-Merdol et al. (2004) 

investigated the uptake and replication of salmonellae in amoebae. Three different serovars of 

Salmonella enterica (Dublin, Enteritidis, and Typhimurium) were evaluated for internalization 

by 5 different isolates of axenic Acanthamoeba species. The Dublin serovar was internalized 

more efficiently than the other two serovars, and the Acanthamoeba rhysodes isolate was more 

efficient than the other four isolates. The researchers concluded that Acanthamoeba species can 

differentiate Salmonella serovars and that internalization of the bacteria produces cytotoxic 

effects mediated by defined bacterial virulence loci. Axelsson-Olsson et al. (2005) studied the 

infection of Acanthamoeba polyphaga by four different Campylobacter jejuni strains. The 

infecting bacterial cells were observed to be actively moving in amebic vacuoles and survived 

longer when cocultured with amoebae than when cultured alone. They indicated that free-living 

amoebae may serve as a nonvertebrate reservoir for Campylobacter jejuni. 

Guan and Holley (2003) examined E. coli O157:H7, Salmonella, Campylobacter, Yersinia, 

Cryptosporidium, and Giardia in animal manure. Of those pathogens considered, E. coli 

O157:H7 was the most persistent in cattle manure regardless of the temperature and manure form 

(solid or slurry) while Campylobacter and Giardia were weakest survivors in manure. The 

authors concluded that holding manure at 25° C for 90 days will render it free from the 

pathogens considered. This has indirect implications for ambient water quality because the 

conditions experienced by pathogens after excretion but before introduction into ambient water 

contribute to the overall likelihood the pathogen will be infectious by the time it potentially can 

reach a human host through recreational contact. 

III.1 Water Environment Affects Pathogen Survivability and Phenotype 

The most common environmental factors studied for their impact on pathogen survival in water 

are pH, salinity, light exposure, and temperature. Additional environmental characteristics that 

may influence pathogen survival, infectivity, and virulence include: UV light (duration, 

intensity), rainfall, runoff, dispersal, suspended solids, turbidity, nutrients, organic content, 
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February 2009 38 

organic foams, water quality, biological community in water column, water depth, stratification, 

mixing (e.g., wind and waves), presence of aquatic plants, biofilms, and predation. 

Thomas et al. (2006) examined extreme rainfall and spring snowmelt in association with 92 

Canadian waterborne disease outbreaks between 1975 and 2001. Accumulated rainfall, air 

temperature, and peak stream flow were used to determine the relationship between high impact 

weather events and the occurrence of waterborne disease outbreaks. For rainfall events greater 

than the 93rd percentile, there was a greater than 2-fold increase in the odds of an outbreak 

compared to rainfall events less than the 93rd percentile. For each degree-day above 0° C, the 

relative odds of an outbreak increased by a factor of 1.007. The odds ratio is small on a per 

degree-day scale, but is notable over longer timeframes. For example, over a 42-day period, a 5° 

C increase in the maximum daily air temperature would result in over a 4-fold increase 

(1.007(5×42) = 4.33) in the relative odds of an outbreak. Stream flow and stream flow peaks did 

not show a difference between cases (outbreaks) and controls (no outbreaks), but there was a 

considerable lack of data on stream flow. 

An overview of the available information for the six key waterborne zoonotic pathogens follows. 

Information concerning these factors is limited for most waterborne pathogens. Thus, in order to 

develop effective control strategies, additional research may be necessary. 

III.1.1 Pathogenic E. coli Survival in the Environment 

Pathogenic E. coli can be expected to survive outside of a host animal anywhere from a few days 

to several weeks, depending upon environmental conditions. Pathogenic E. coli seem to interact 

with the environment in a similar fashion to nonpathogenic E. coli and do not lose their virulence 

during prolonged survival in the environment. Survival of E. coli O157:H7 in surface waters 

was found to be longer at lower temperatures (Czajkowska et al., 2005) and was 2 to 3 times 

longer in river and lake sediments at the same temperatures (see Table III.1.1-1). 

Table III.1.1-1. Survival of E. coli O157:H7 in Ambient Waters 

Water matrix °C Days to Decrease Reference 

99% 99.99% 

Surface waters (lakes and rivers) 6 4-11 8-22 

Czajkowska et al., 2005 Surface waters (lakes and rivers) 24 2-8 5-10 

Sediments (same lakes and rivers) 6 10-20 25-39 

Sediments (same lakes and rivers) 24 5-8 10-30 

River water with feces 15 7.5 14.5 McGee et al., 2002 

Unfiltered lake water 8 91 NA 

Filtered tap water 15 >91 NA Wang and Doyle, 1998 

Unfiltered lake water 25 14-28 NA 
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February 2009 39 

Although direct contamination of ambient water due to domestic animals or livestock wading in 

water is possible, most contamination of water is due to runoff from pastures and fields after land 

application of manure. E. coli O157:H7 can survive for at least several weeks in animal feces 

and slurries (Avery et al., 2005) and has been demonstrated to survive at least 500 days at -20° C 

in frozen soil (Gagliardi and Karns, 2002). 

III.1.2 Campylobacter Survival in the Environment 

Campylobacter has been shown to survive in aquatic environments with low temperatures (4° C) 

between 8 days (Buswell et al., 1998) and 4 months (Rollins and Colwell, 1986). 

Buswell et al. (1998) found that survival times of Campylobacter isolates differed by 2- to 4-fold 

depending on the combination of temperature and oxygenation tested. The mean survival times 

in sterile microcosms were 202 hours at 4° C, 176 hours at 10° C, 43 hours at 22° C, and 

22 hours at 37° C. The survival times were considerably longer in the presence of the 

autochthonous water microflora (two strains tested survived 700 and 360 hours at 4° C). 

Aerobic conditions decreased the survival of one strain 30 percent and increased the persistence 

of another strain by more than 3-fold. Within biofilms, the pathogen persisted up to the 

termination of the experiments after 28 and 42 days of incubation at 30 and 4° C, respectively. 

Rollins and Colwell (1986) found that Campylobacter incubated in filter-sterilized stream water 

was recoverable after 4 months at 4°C. Incubation at 25°C resulted in a decline to the 

nonculturable state within 28 days, and at 37°C, the nonculturable state was reached in 10 days. 

Direct counting methods indicate that the nonculturable but viable state of Campylobacter is 

significant. 

III.1.3 Salmonella Survival in the Environment 

Salmonella are also found frequently in sewage, soil, and various surface waters. The greatest 

source of the bacteria is fecal contamination. Under suitable environmental conditions, 

Salmonella can survive for weeks in waters or years in soils (Lightfoot, 2004). Salmonella grow 

at temperatures ranging from 10 to 43o C, but some serovars have suppressed growth at 

temperatures above 40o C (Covert and Meckes, 2006). Salmonella can grow at pH 4–8 and at 

water activities above 0.93. Under some conditions, Salmonella may proliferate below 4 o C and 

survive below pH 4 (Lightfoot, 2004). 

III.1.4 Leptospira Survival in the Environment 

Leptospira survive longer in the environment in warm, humid conditions. Leptospirosis is 

seasonal, which relates to the pathogen’s survival in the environment. In temperate regions, 

there is a peak during summer or fall, whereas in warm-climate regions, the rainy season is 

associated with peaks because dessication decreases pathogen survival (Levett, 2001). 

Ganoza et al. (2006) compared levels of Leptospira in urban and rural environmental surface 

waters in the Peruvian Amazon region of Iquitos. The concentration of pathogenic Leptospira

was higher in urban than rural water sources and rats were the indicated zoonosis. 
U.S. Environmental Protection Agency

February 2009 40 

III.1.5 Cryptosporidium Survival in the Environment 

As noted previously, because Cryptosporidium oocysts are extremely resistant to environmental 

or engineered degradation, the survival of Cryptosporidium under a variety of environmental and 

drinking water treatment conditions has been evaluated by many investigators. While the 

majority of these studies have considered the effects of physical antagonism (e.g., freezing, 

heating, UV exposure), studies have also been conducted to consider the role of microbial 

antagonists (microbial predation), chemical antagonists (such as disinfection), and aging. This 

section focuses primarily on aspects of physical antagonists in the environment because they are 

most pertinent to the topic of this paper. 

Robertson et al. (1992) evaluated the sensitivity of C. parvum oocysts to a variety of 

environmental pressures such as freezing, dessication, and water treatment processes, as well as 

in physical environments commonly associated with oocysts. Approximately 97 percent of the 

test oocysts were inactivated after 18 days at 22° C, suggesting that the levels of viable oocysts 

in surface waters might be influenced by seasonal temperature variations. After 2 hours of 

drying oocysts at room temperature, only 3 percent of oocysts were still viable, and after 4 hours, 

no oocysts were viable. When stored at 4° C, the percentage of oocysts remaining viable in stool 

samples decreased steadily with time. (In the study, the relationship between oocyst viability 

and time varied with individual.) After 176 days in tap water, river water, or cow feces, there 

was a statistically significant increase in the proportion of dead oocysts in test samples. 

Seawater was even more lethal to oocysts, with a statistically significant increase in dead oocysts 

by 35 days of exposure to the test conditions. C. parvum oocyst viability is sensitive to a wide 

range of typical environmental conditions while remaining relatively insensitive to some water 

treatment processes. Robertson et al. (1992) also emphasized that oocyst viability depends on 

the amount of time to which oocysts are exposed to a physical or chemical stress in the 

environment. 

Temperature has a significant effect on oocyst survival, with (unfrozen) colder waters promoting 

the highest survival rates (USEPA, 2001a). Warm and boiling water completely neutralizes 

oocysts, and the temperature of the water determines the time required for the treatment to 

become effective (Anderson, 1985). Cryopreservation studies conducted by Fayer et al. (1991, 

1997) indicate that oocyst survival depends on the temperature and duration of freezing 

conditions, implying that C. parvum oocysts are not necessarily rendered noninfectious by being 

frozen per se. In another study, Fayer and Nerad (1996) demonstrated that the infectivity of C. 

parvum oocysts after freezing is dependent on the temperature and duration of freezing. In 

general, shorter freezing times are required to neutralize infectivity when lower freezing 

temperatures are employed (e.g., 1 hour at -70° C versus 168 hours at -15° C to completely 

neutralize infectivity) (Fayer and Nerad, 1996). 

Temperature stability studies also were conducted by Sattar et al. (1999) who evaluated the 

freeze/thaw susceptibility of various preparations of oocysts including highly purified 

preparations as well as infected calf feces. The results of this study indicated that oocyst stability 

under freezing conditions is at least partially dependent upon the surrounding matrix, with fecal 

material conferring a cryopreservative effect on oocysts. In the absence of freezing conditions, 

colder water temperatures tended to promote the survival of most microorganisms. In water, C. 
U.S. Environmental Protection Agency

February 2009 41 

parvum may survive outside of mammalian hosts for several months or more depending upon 

water temperature (Straub et al., 1994). 

Fayer et al. (1998) investigated the effect of water temperatures ranging from -10 to 35° C and a 

few higher temperatures on oocyst infectivity. As water temperature was increased from -10 to 

20° C, oocysts remained infectious for longer exposure times. For example, oocysts retained 

their infectivity for only 1 week when suspended in water held at -10°C but remained infectious 

for up to 24 weeks in 20° C water. As water temperatures were increased above 20° C, oocysts 

retained their infectivity for shorter exposure times (Fayer et al., 1998). Under conditions of 

high water temperatures, higher than typically found in surface waters, Fayer (1994) indicated 

that all evidence of C. parvum infectivity was lost within 60 seconds when temperatures 

exceeded 72° C or when temperatures of at least 64° C were maintained for 2 minutes. 

Holding oocysts to 45°C for 5 to 20 minutes was effective in completely neutralizing infectivity 

(Anderson, 1985). Anderson (1986) examined the infectivity (determined in infant mice) of 

oocysts from calf fecal samples that had been dried in a barn (< 60 percent humidity) in either 

winter or summer months. In summer temperatures (i.e., 18 to 29° C), oocysts completely lost 

infectivity in 1 to 4 days. Experiments conducted in winter, with air temperatures ranging from -

1 to 10° C, demonstrated a complete loss of infectivity within 2 to 4 days. Control samples kept 

moist and refrigerated retained infectivity for up to 2 to 3 weeks. 

Limited studies have been conducted on the effects of physical shear on oocyst viability; these 

studies have attempted to assess the potentially abrasive effects of oocyst contact with sand and 

gravel particles or through fast-flowing waters. Parker and Smith (1993) found that after shaking 

with sand for 5 minutes, 90 minutes, and 2 hours, the number of non-viable oocysts increased 

significantly to 50 percent, 99.7 percent, and 100 percent, respectively. When chlorination 

followed 5 minutes of sand shaking, the observed non-viable oocysts increased to 68 percent. 

When oocysts were on an orbital shaker at 60 and 120 rpm, oocyst viability declined linearly 

over the course of an hour, with approximately 50 percent loss of viability noted at 20 minutes 

(Sattar et al., 1999). These authors also showed that oocysts subjected to 2000 psi (13.9 Mpa) 

for 1 minute had little reduction in viability. 

Sattar et al. (1999) also evaluated the effects of microbial predation on oocyst survival. They 

observed that oocysts incubated in dialysis cassettes that were suspended in natural waters 

exhibited significantly longer survival times when bacterial populations were excluded from the 

suspension water. The observation implies that microbial predation may play an important role 

in reducing oocyst survival in ambient (natural) waters. 

Nasser et al. (2007) examined the effect of sunlight and salinity on the die-off of C. parvum. 

Experiments were carried out for 7 days in tap and seawater and sunlight and dark conditions. 

Oocyst die-off was greatest when exposed to seawater and sunlight (0.44 log/day); oocysts in tap 

water in the dark, exposed to sunlight, and oocysts in seawater in the dark had die-off rates of 

0.1, 0.22, and 0.19 log, respectively. At the end of the 7-day study period, a 3 log reduction in 

infectivity was measured in the sunlight- and seawater-exposed oocysts. Cryptosporidium

oocysts retain substantial infectivity for several months at salinity levels corresponding to 

estuarine coastal waters (Fayer, 2004a) and for several weeks in seawater (WHO, 2006). These 
U.S. Environmental Protection Agency

February 2009 42 

studies indicate that Cryptosporidium can thus pose a serious health hazard to humans by direct 

and indirect contact in recreational waters. 

King et al. (2005) measured oocyst inactivation rates in reagent-grade and environmental waters 

over a range of temperatures. Oocysts incubated at 4 and 15° C remained infective over a 12-

week holding period. A 4 log10 reduction in infectivity was observed for both 20 and 25°C 

incubation treatments at 12 and 8 weeks, respectively, for all water types examined. This is a 

faster rate of inactivation for oocysts than had been previously reported. Inactivation at higher 

temperatures is likely a function of increased oocyst metabolic activity. 

Li et al. (2005) measured the inactivation rate of bovine C. parvum oocysts subjected to 

temperature regimes designed to mimic the diurnal oscillations of ambient temperature in bovine 

feces exposed to sunlight in commercial cattle operations in California. No infectious oocysts 

were observed after 1- to 5-day cycles of 40, 50, 60, and 70° C. The loss of infectivity was 

primarily due to partial or complete in vitro excystation during the first 24-hour diurnal cycle and 

secondarily to thermal inactivation of the remaining intact or partial oocysts. The results suggest 

that as ambient conditions generate internal fecal temperatures greater than or equal to 40° C, 

rapid inactivation occurs at a rate equal to or greater than 3.27 log10 reduction per day for C. 

parvum oocysts deposited in the feces of cattle. 

Méndez-Hermida et al. (2005) reported on batch-process solar disinfection of .C. parvum oocysts 

in water. Oocyst suspensions were exposed to simulated sunlight (830 W/m2

) at 40° C. 

Viability assays and infectivity tests indicated that exposures of 6 and 12 hours reduced oocyst 

infectivity from 100 percent to 7.5 percent and 0 percent, respectively. 

The behavior of lake inflows is important in determining pathogen transport and distribution. 

Inflows that are warmer than the lake water will move over the surface of the lake, whereas 

inflows that are colder than the lake will sink beneath the surface layer where they will flow 

along the bottom towards the deepest point (Brookes et al., 2004). The fate of pathogens in lakes 

is determined by factors such as settling and inactivation by temperature, UV, and predation by 

other microorganisms. Brookes and colleagues found that inactivation of Cryptosporidium by 

UV light can be rapid or slow, depending on the depth of the oocysts in the water column and the 

extinction coefficient for UV light. 

Pokorny et al. (2002) investigated the effects of temperature on oocysts stored in the dark in 

filter-sterilized and nonfilter-sterilized river water. They reported that as the temperature was 

increased from 4 to 23° C, the infectivity of oocysts decreased; no infectious oocysts were 

detected after 1 week at -20° C. 

Excreted Cryptosporidium oocysts can survive for substantial periods in animal wastes and soils. 

Thus, contaminated runoff can enter ambient water and result in potential human exposures. The 

numbers of oocysts excreted by infected young animals may be especially large, between 1 and 

10 million oocysts per gram of feces (WHO, 2006). Oocyst survival for 4 weeks or more has 

been documented in concentrated animal wastes, particularly at low temperatures (4° C) (WHO, 

2006). In the environment, the vast majority of oocysts (99 percent) are inactivated by repeated 

freeze-thaw cycles independent of the number of times the soil was frozen (Fayer, 2004a). 
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Therefore, Cryptosporidium may be environmentally limited in parts of the United States during 

the winter season. There is evidence that in warmer ambient temperatures, between 4 and 20° C, 

very little inactivation of oocysts occurs in different types of agricultural soils (Jenkins et al., 

2002; WHO, 2006). Factors that are known to reduce oocyst survival in soils include drying and 

basic pH (Fayer, 2004a). Oocyst survival in various water matrices is highly variable, but 

survival for longer than 30 days has been demonstrated in several studies. Approximately 4 to 5 

percent of oocysts in tap water and river water samples survived after approximately 6 months, 

with approximately 37 percent inactivation after 2 days exposure to tap water (USEPA, 2005a, 

2005b). 

Walker et al. (2001) tested oocyst degradation (as indicated by microscopic examination) in 

response to the combined stresses of water potential (sodium chloride solute potential), abovefreezing temperatures (4 and 30° C), and a subfreezing temperature (-14° C) for different freeze 

thaw cycles (-14 to 10° C). The degradation coefficients were estimated using multiplicative 

error and exponential decay models. Increased water potential increased the rate of C. parvum

population degradation for all temperature conditions investigated. The effects of water potential 

were roughly four times those noted for freezing alone. The difference between the effects of 

freeze-thaw cycling and simple freezing may be caused by mechanical damage to the oocyst 

wall. The authors conclude that water potential conditions encountered under field conditions 

are likely to lead to more rapid degradation of oocyst populations than might be expected from 

studies of degradation in calf feces, distilled water with antibiotics, and reverse osmosis water at 

low temperatures. 

III.1.6 Giardia Survival in the Environment 

Studies of the effect of temperature and other environmental factors on Giardia cyst survival 

were summarized in EPA’s Giardia Human Health Criteria Document (USEPA, 1998). Survival 

was determined based on dye inclusion/exclusion, excystation, or animal infectivity studies. 

Some studies used Giardia muris cysts, whereas others used Giardia lamblia cysts. Overall, the 

studies on the effect of temperature indicated that survivability decreased as temperature 

increased and that while some cysts could survive a single freeze-thaw cycle, repeated freezethaws as might be expected in the environment would likely inactivate cysts (USEPA, 1998). 

Johnson et al. (1997) investigated the survival of cysts in marine waters and determined that 

viability was reduced 99.9 percent in 3 hours in marine waters exposed to sunlight (as reported in 

USEPA, 1998). They also found that 77 hours were required to get 99.9 percent inactivation in 

the dark and that cysts survived longer at a salinity of 28 mg/L than at 35 mg/L. Because 

different waters were used in the experiments, however, these investigators could not rule out the 

effect of factors other than salinity. 

Olson et al. (1999) found that Giardia cysts were noninfective in water, feces, and soil following 

1 week of freezing to -4° C and within 2 weeks at 25° C. At 4° C, Giardia cysts were infective 

for 11 weeks in water, 7 weeks in soil, and 1 week in cattle feces. Robertson and Gjerde (2006) 

tested survival of Giardia cysts (as well as Cryptosporidium oocysts) during winter in an aquatic 

environment (approximately 1 to 7° C) in Norway. Three conditions were compared, distilled 

water, river water, and submersion of a filter chamber containing cysts into the river. The rate of 

decline in viability was similar under all three conditions, and no Giardia cysts with apparently 
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viable morphology could be detected after 1 month. Boiling Giardia for 1 minute reduces 

viability (as determined by flurogenic dyes) to less than 1 percent and renders them 

noninfectious (as determined by animal infectivity) (El Mansoury et al., 2004). Storage at 4° C 

and -4° C for up to 7 days preserves Giardia cyst viability and infectivity. Storage at 30 ppt 

(parts per thousand) salinity for 4 weeks decreased viability to 30 percent, but all animals were 

infected. Storage at 50 ppt salinity for 4 weeks decreased viability to 5 percent and 80 percent of 

animals were infected. Storage at 50 ppt salinity for 4 weeks resulted in zero viability (El 

Mansoury et al., 2004). 

III.1.7 Virus Survival in the Environment 

Viruses are more stable at lower temperatures; however, different viruses have different 

stabilities under similar environmental conditions. For example, astroviruses survive longer than 

poliovirus and adenovirus, but shorter than rotavirus and hepatitis A virus (Sobsey, 2006). For 

poliovirus and parvovirus, 90 percent inactivation was observed after 1 to 3 days at 28° C, and 

90 percent inactivation was observed after 10 days at 6° C (Griffin et al., 2003). Parvoviruses 

are the most heat stable enteric viruses known (Gerba, 2006a). Enterovirus nucleic acid is 

detectable for 60 or more days, whereas infectious virus is detectable for 51 days or less (Griffin 

et al., 2003). Below 5° C, enteroviruses can survive for years (Gerba, 2006b). Limited data 

suggests that adenoviruses survive longer in water than enteroviruses and hepatitis A virus 

(Enriquez and Thurston-Enriquez, 2006). 

Pesaro et al., (1995) evaluated the persistence of five animal viruses, representing picorna-, rota-, 

parvo-, adeno-, and herpesviruses, and the coliphage f2, using a filter sandwich technique that 

mimics the environment in various states of manure. Depending on ambient temperature, pH, 

and type of animal waste, 90 percent reduction of virus titer varied, ranging from less than 1 

week for herpesvirus to more than 6 months for rotavirus. Virus inactivation was faster in liquid 

cattle manure, a mixture of urine and water (pH > 8.0), than in semiliquid wastes that consisted 

of mixtures of feces, urine, water, and bedding materials (pH < 8.0). The authors conclude that 

viruses contained in manure may persist for prolonged periods of time if stored under nonaerated 

conditions and this may lead to environmental contamination with viruses. 

III.2 Host Animals Can Influence Pathogen Characteristics and Mechanisms of Rapid 

Evolution 

There is evidence that zoonotic pathogens may change in infectivity, virulence, and the severity 

of disease caused in humans depending on their previous host environment. There is also 

evidence that some of these host-factor changes can influence subsequent infection cycles in 

exposed hosts. For example, in laboratory experiments using nutritionally deficient mice 

(selenium-deficient or vitamin E-deficient), Morse (1997) reported that a normally avirulent 

(mild) coxsackievirus B3 isolate gave rise to a virulent variant, albeit through an unknown 

mechanism. The virulent variant resembled other known virulent genotypes and was stable upon 

subsequent infection of other mice with adequate nutrition. In another demonstration of host 

influence on pathogen evolution, yeast with deletions in genes that normally suppress viral RNA 

recombination became “hotbeds” for viral recombination. The host (in this case yeast) genes 

could affect viral recombinant accumulation by up to 80-fold (Serviene et al., 2005). The key 
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February 2009 45 

mechanisms of phenotypic change in pathogens are genetic diversity (coinfection and 

quasispecies), cryptic genes, mutators, and epigenetic effects, and are summarized as follows. 

Genetic diversity (co-infection and quasispecies): The pathogen population within a single 

host can be comprised of several or even numerous genetic variants of the same zoonotic 

pathogen. This variation can occur when the infectivity is such that several genotypes 

coinfect the host simultaneously, then “compete” or “cooperate” as infection progresses. The 

fluctuations in genotype prevalence depend on host-pathogen interactions as some genotypes 

gain dominance and others become rare. High genetic diversity also can occur when 

pathogens have high mutation rates. This latter phenomenon, referred to as “quasispecies,” 

occurs mainly in RNA viruses because viral RNA replicase enzymes lack proofreading 

functions during replication, which leads to high mutation rates (Domingo et al., 1998; 

Morse, 1997). For example, caliciviruses may have as many as 1 to 10 mutations per 

template copy (Smith et al., 1998), and within-person HEV sequence diversity has been 

documented to range from 0.11 to 3.4 percent (Grandadam et al., 2004). For retroviruses, 

every virus particle may be genetically different from every other particle. In fact, the 

cooperativity6

 of many virus particles’ genetic material may be necessary to complete the 

infection process (Lederberg, 1998). 

Cryptic genes: Meiotropy is the ability of an organism to gain a phenotypic trait through 

mutation (Brubaker, 1991). One example of a cryptic gene is the yopA gene in Yersinia 

pseudotuberculosis. A stretch of deoxyadenosine nucleotides (DNA base A) can 

spontaneously change in length between 8 and 9 bases, which can result in the absence or 

presence of the gene product. In Y. pseudotuberculosis, the absence of the gene product 

results in increased virulence.7 In Y. pestis (plague), the gene yopA is not normally 

expressed; however, molecular manipulation that causes expression of the yopA gene 

product reduces the virulence of Y. pestis. Thus, it is possible that endemic hosts of Y. pestis 

could harbor a strain of lower virulence, which by one mutation could become hypervirulent 

and potentially cause an outbreak of plague (Rosqvist et al., 1988). Another example is in 

Salmonella, in which flagellar antigens can be expressed or silenced in a reversible manner 

by inversion of a segment of DNA that moves the promoter from one locus to another 

(Lederberg, 1998). This type of genetic rearrangement may serve as a mechanism of phase 

variation for antigenic factors in the bacteria. More standard transcriptional control of the 

gene expression might allow for low levels of transcriptional leakage and small quantities of 

antigen to be produced. Prior trace levels of antigens could be sufficient to promote host 

immunity. Bacteria carry site-specific recombinases that are capable of scrambling bacterial 

genomes in order to suppress and unsuppress genes. 

Mutators: Several genes have been identified that influence the mutation rate of bacteria. 

For example, bacterial cells that carry the MutD5 protein, which binds to DNA polymerase, 

accumulate a broad spectrum of base substitutions and frameshift mutations (the mutation 

 6

 The hypothesis that swarms of viral genotypes cooperate to comprise an “average phenotype” differs from 

quorum sensing, which is the coordination of bacterial cells via cell-to-cell communication with small signaling 

molecules to form biofilms and other group-related phenotypes. 7

 In this case, the presence of the gene leads to decreased virulence because the gene product facilitates chronic 

infection, which is less severe than acute infection. 
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frequency can be 20- to 4,000-fold) (Selifonova et al., 2001). Mutator strains can pass 

genetic material to other bacteria and thus transfer the mutator trait. Therefore, the ability of 

bacteria to evolve rapidly is heritable. 

Epigenetic effects: Epigenetic effects are reversible, heritable changes in gene regulation that 

occur without a change in DNA sequence. Genomic imprinting through DNA methylation is 

one type of epigenetic effect that has been documented for pathogen regulation of virulence 

(Low et al., 2001). The zoonotic bacteria E. coli, S. enterica (serovar Typhimurium), Vibrio 

cholerae, Y. pseudotuberculosis, Y. enterocolitica, Helicobacter pylori, and Campylobacter

are a few notable pathogens for which DNA methylases are known to regulate gene 

expression (Fälker et al., 2005; Low et al., 2001). Although DNA methylase promoters are 

known to be responsive to in vivo growth conditions, the degree to which host factors 

influence pathogen DNA methylation and whether those methylation patterns provide a 

memory system for subsequent generations of pathogens are not known. 

All of these mechanisms can contribute to rapid evolution of zoonotic pathogens.8

 Rapid 

evolution is most often observed in new hosts, where new stresses are thought to lead to strong 

selection and rapid evolution (Ebert, 1998). Evolution in new host environments can lead to a 

reduction of virulence when the original host is encountered again. Serial passage experiments 

(SPEs) often result in attenuation of pathogenicity in one host along with an escalation of 

pathogenicity in the new host.9 Attenuation can be so severe that it can even lead to an altered 

host range (complete loss of ability to infect the original host species).10 In SPEs when only one 

or a few pathogens are transferred at each passage, however, genetic drift can result in decreased 

genetic variability and lead to a failure to adapt to new hosts and a decline in overall pathogen 

fitness. Text Box III.2-1 summarizes some feeding studies done in humans and pigs with 

zoonotic parasites. The examples help illustrate how changes in laboratory isolates due to 

passage through hosts should be considered during experimental design. 

Although SPEs are useful for studying pathogen evolution, the trends observed in SPEs are not 

necessarily broadly applicable to pathogen evolution as a whole (Ebert, 1998). In fact, the 

observation that virulence increases in SPEs in new hosts seems contrary to the classic 

expectation that pathogens and hosts evolve over time in ways that render infections benign 

(Dieckmann, 2002; Wills, 1996). Currently, evolutionary biologists estimate the evolutionary 

success or failure (i.e., “fitness”) of pathogens by their rate of spread through a given host 

population. Low virulence can lead to missed opportunities to spread due to low pathogen 

numbers. High virulence can lead to host death and a subsequent lack of spread. Those 

hypotheses are supported by the observation that intermediate levels of pathogen virulence can 

be stable. Thus, the dynamic between pathogen and host drives pathogen (and host) evolution 

 8

 For the purpose of this paper, rapid changes are phenotype (or genotype or epigenetic) changes that occur 

within one or a few passages of a zoonotic pathogen through a particular host species. 9

 The negative correlation in the fitness of a pathogen in different hosts is the antagonistic pleiotropy 

hypothesis—a gene that enhances fitness in one host decreases fitness in the other host (Ebert, 1998). 10 Live vaccines such as Theiler’s yellow fever vaccine and Sabin’s polio vaccine are examples of attenuated 

pathogens that elicit an immune response without inducing disease. However, reemergence of pathogen virulence 

after vaccination remains a risk (Ebert,1998). 
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and is influenced by numerous factors including the infection status of the host population as a 

whole (Dieckmann, 2002). 

Because pathogens can evolve quickly within one host, it is reasonable to suspect that zoonotic 

pathogen pools that were propagated in animals would be different from pathogen pools that 

came from human sources. However, the extent to which known waterborne zoonotic pathogens 

are attenuated or gain enhanced virulence in humans when passing through animal hosts remains 

unknown. Even if general trends could be characterized, it is unlikely that differences could be 

quantified adequately in the near-term to predict differences in human infectivity and virulence 

for pathogens passing through different host animals. 

Another mechanism by which virulence and fecundity of a microorganism may be affected was 

recently reported by Jenkins et al. (2007) for C. parvum. These investigators infected dairy 

calves with oocysts from either C. parvum Beltsville (B) or C. parvum Iowa (I). Calves given 

the B isolate excreted 5-fold more oocysts than those receiving the I isolate. Quantitative reverse 

transcriptase-PCR indicated that the B isolate contained a 3-fold greater number of the symbiont 

C. parvum virus (CPV) than the I isolate. They concluded that CPV may have a role in fecundity 

and possibly virulence of C. parvum. The authors indicated that their results contrasted to those 

found by Miller et al. (1988) in which there was an inverse relationship between presence of a 

Giardia lamblia virus (GLV) and parasite growth. Miller et al. (1988) used virus-free isolate 

that they infected with various numbers of GLV, and Jenkins et al. (2007) noted that virus-free 

cysts may be more susceptible to the effects of virus infection. Jenkins et al. (2007) also 

indicated that C. hominis and C. parvum, the two species most often associated with human 

infections, are the only species reported thus far to be infected by CPV. 
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Text Box III.2-1. Examples of Feeding Studies with Zoonotic Parasites 

For the widespread waterborne zoonotic protozoa Cryptosporidium and Giardia, human volunteers 

(immunocompetent adults) have been exposed to measured doses of various strains of Cryptosporidium and to 

a single Giardia isolate to evaluate their dose-response relationships. However, there are uncertainties 

associated with characterizing dose even in clinical settings. Microbes can exhibit variability in infectivity, 

virulence, or environmental survival within strains; even for “pure isolates,” batches can differ. For 

microorganisms that cannot survive freezer storage or do not maintain their genetic integrity in freezer storage 

or tissue culture, in vivo passage in animals is required to maintain stocks. Even if the starting inoculum for a 

dose-response study is clonal, mutations will occur that may impact pathogen characteristics. When the 

starting inoculum is not clonal, which is most often the case, the subpopulation ratios within an individual host 

can differ from other hosts receiving the same inoculum. The subpopulation ratios also may vary as infection 

progresses, so collecting pathogens from a host on one day may not yield the same pool of pathogens as 

collecting on another day. In addition, some pathogens are not amenable to storage or maintenance in 

laboratory settings under any conditions and must be continuously collected from the field for each experiment. 

Although the challenges of properly characterizing and controlling pathogen variability in experimental research 

settings are considerable, the challenges are even greater for epidemiological studies. 

Cryptosporidium in Humans 

Data on the infectivity of Cryptosporidium in humans are available from studies conducted at the University of 

Texas, Houston, by DuPont, Chappell, Okhuysen, and colleagues. These studies all involved healthy adult 

volunteers ingesting different numbers of Cryptosporidium oocysts. Subjects were then evaluated for 

Cryptosporidium in stool samples and for diarrheal and other GI illness symptoms. Infectivity was estimated for 

five C. parvum isolates: TAMU (collected from a veterinary student); Iowa (derived from a calf); UCP (derived 

from a calf); Moredun, (collected from a red deer calf); 16W (from a calf); and TU502 (an isolate collected from 

an infected child and propagated in gnotobiotic piglets [Chappell et al., 2006]). Cryptosporidium from animal 

sources were found to be infectious in humans. No attempt was made to evaluate differences in potential 

infectivity due to repeated passage in animal hosts. However, the UCP isolate was less infectious in humans 

than the other isolates, and EPA’s Science Policy Council speculated that this could be due to prolonged 

maintenance in calves. In the risk assessment that was conducted in support of EPA’s Long Term 2 Enhanced 

Surface Water Treatment Rule (LT2) Economic Analysis, a dose-response relationship was chosen that weighs 

the UCP data less than the other isolates. 

Cryptosporidium in Animals 

Akiyoshi et al. (2003) investigated mixed infections of Type 1 (C. hominis) and Type 2 (C. parvum) in gnotobiotic 

piglets. In all the time intervals tested, Type 2 displaced Type 1, even if Type 1 was permitted to become 

established before inoculation with Type 2. This result raises significant questions regarding the relative 

perpetuation and survival of the two genotypes in mammalian hosts. The same researchers noted that field 

technicians very readily became infected with C. hominis, but that cross-contamination of C. hominis with C. 

parvum in the animals used to maintain stocks resulted in C. parvum overwhelming C. hominis (Tzipori, 2000). 

These observations suggest that discovering the mechanisms by which C. hominis is maintained in natural 

setting when C. parvum is also present should improve understanding of risks to humans. 

Giardia in Humans 

Rendtorff (1954) conducted a controlled, clinical study of male prison volunteers who were fed Giardia cysts 

obtained from a human source. Giardia cysts of known numbers varying from 1 to 106

 were placed into gelatin 

capsules along with a small amount of saline. The capsules were given to the volunteers along with 4 to 6 

ounces of water. Control subjects were given sterile saline in the same manner. A dose of 10 cysts was found 

to be sufficient to produce human infection, as determined by observing the presence of Giardia in fecal smears 

(Rendtorff, 1954). However, because cyst viability could not be determined prior to administration to volunteers, 

the failure to elicit infection in the five men treated with a dose that was calculated to contain only one cyst may 

have been due to dosing with inactive cysts. The Giardia Assemblages used in these studies are not known but 

presumably are A or B because these are the Assemblages known to infect humans.
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IV. SUMMARY

Contamination of recreational waters with feces from warm-blooded animals poses a risk of 

zoonotic infection of humans with some of the pathogens in those waters. Although the risk and 

severity of human illness due to contamination with animal feces and zoonotic pathogens is most 

likely lower than the risk and severity of illness from treated or untreated human sewage, 

currently available data are insufficient to quantify the differences. At present, the six most 

important zoonotic waterborne pathogens are the following: 

• Pathogenic E. coli;

• Salmonella;

• Campylobacter;

• Leptospira;

• Cryptosporidium; and

• Giardia. 

All of these waterborne pathogens are likely to cause more severe symptoms in children and 

immunocompromised individuals and subpopulations than in the remainder of the population. 

Of these six, pathogenic E. coli has the most potential for severe adverse health effects that can 

even be fatal. Potential debilitating chronic sequelae such as Guillain-Barré Syndrome and 

reactive arthritis have been associated with Campylobacter infections. Although the most 

common recreational illnesses are probably due to human viruses causing short-term GI, the 

waterborne zoonotic pathogens discussed in this report have the potential to cause serious health 

effects. While serious health outcomes are likely to be rare in comparison with self-limiting 

illnesses as a result of ambient (recreational) water exposure, the adverse health impacts of the 

rare, but more serious illnesses remain an important public health challenge. 
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February 2009 50 

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U.S. Environmental Protection Agency

February 2009 A-1 

APPENDIX A 

WATERBORNE PATHOGENS 

As described in Section I.2 of this paper, four attributes were used to select the waterborne 

zoonotic pathogens of concern for recreational uses of ambient waters (partially adapted from 

Bolin et al., 2004a). Table A-1 lists all the pathogens that were evaluated for potential inclusion 

in this paper. Information provided in Table A-1 includes whether the pathogen is considered 

waterborne, the species that are zoonotic hosts, whether the zoonotic hosts are warm-blooded, 

what illnesses the pathogen causes in humans, and the importance of considering the pathogen as 

EPA decides whether animal sources of fecal material should be considered differently from 

human sources for CWA §304(a) AWQC. 
U.S. Environmental Protection Agency

February 2009 A-2 Table A-1. Known and Potential Zoonotic Waterborne Pathogens 

Type Pathogen Waterborne Zoonotic Host

Zoonotic 

Host is 

WarmIllnesses and Symptoms in Humans (less U.S. Outbreaks 

blooded common symptoms) s

Bacteria Acinetobacter Yes None NA Septicemia, Hospital N

(generally in meningitis, settings environment) endocarditis, brain 

abscesses, pneumonia, empyema, urinary tract infections, eye infections, and skin and wound infections 

Bacteria Aeromonas Yes 

(generally in environment) 

None NA Gastroenteritis 

(septicemia) 

None reported 

N

Bacteria Campylobacter Yes Poultry, cattle, Yes Diarrhea, Mainly Im

sheep, and abdominal pain, foodborne wild birds malaise, fever, and drinking 

nausea, and water vomiting (typhoidlike syndrome, febrile convulsions, meningeal arthritis, reactive arthritis, and GBS) 

Bacteria Cyanobacteria Yes None NA Rash and Drinking N

(generally in gastroenteritis water and environment) recreational 

water 
U.S. Environmental Protection Agency

February 2009 A-3 

Type Pathogen Waterborne Zoonotic Host

Zoonotic 

Host is 

Warmblooded 

Illnesses and Symptoms in 

Humans (less 

common 

symptoms) 

U.S. 

Outbreaks 

s

Bacteria Verotoxin-producing E.coli

(VTEC) – includes enterohemorrhagic E. coli

(EHEC), including O157:H7 

Yes Cattle, 

chicken, sheep, pigs, horses, dogs, and deer 

Yes Diarrhea (bloody), 

severe abdominal cramping, headache, hemorrhagic colitis, and hemolytic uremic syndrome 

Foodborne and waterborne (drinking water and recreational water) 

Im

Bacteria Enterotoxigenic E. coli

(ETEC) 

Yes Same as 

VTEC 

Yes Acute, watery 

diarrhea 

Waterborne P

im

Bacteria Attaching and effacing E. 

coli (A/EEC) 

Yes Same as 

VTEC 

Yes Acute or persistent 

diarrhea 

No waterborne reported 

Pim

Bacteria Enteropathogenic E. coli

(EPEC) 

Yes Same as 

VTEC 

Yes Acute or persistent 

diarrhea 

Waterborne P

im

Bacteria Enteroaggregative E. coli 

(EAggEC) 

Yes Same as 

VTEC 

Yes Acute, watery, and 

often protracted diarrhea 

No waterborne reported 

Pim

Bacteria Diffuse adherent E. coli 

(DAEC) 

Yes Same as 

VTEC 

Yes Acute or persistent 

diarrhea 

No waterborne reported 

Pim

Bacteria Enteroinvasive 

(EIEC) 

E. coli Yes None NA Acute, often 

inflammatory diarrhea; dysentery 

No waterborne reported 

N
U.S. Environmental Protection Agency

February 2009 A-4 

Type Pathogen Waterborne Zoonotic Host

Zoonotic 

Host is 

Warmblooded 

Illnesses and Symptoms in 

Humans (less 

common 

symptoms) 

U.S. 

Outbreaks 

s

Bacteria Flavobacterium Yes None NA Gastroenteritis, 

meningitis, pneumonia, endocarditis, and septicemia 

Rare waterborne (stagnation in drinking water), hospital settings more 

N

common 

Bacteria Helicobacter pylori Possibly Weak 

evidence for ferrets, racoons, swine, sheep, rodents, and primates 

Yes Gastric disorders, 

pepticand duodenal ulcer disease, lymphoma of the digestive tract, and ademenocarcinoma of the stomach 

No waterborne reported 

N

Bacteria Klebsiella Yes 

(generally in environment) 

Warm-blooded animals 

Yes Infections in 

respiratory system, genitourinary tract, nose, and throat, (meningitis and septicemia) 

Hospital settings 

N

Bacteria Legionella Yes None NA Legionellosis, 

pneumonia, Legionnaire’s disease, and Pontiac fever 

Hospitals, pools, and spas 

N

Bacteria Leptospira Yes Rats, dogs, 

raccoons, swine, and cattle 

Yes Leptospirosis 

(Weil’s disease) 

Recreational waterborne over 50% of cases in 

Im

Hawaii 
U.S. Environmental Protection Agency

February 2009 A-5 

Type Pathogen Waterborne Zoonotic Host

Zoonotic 

Host is 

Warmblooded 

Illnesses and Symptoms in 

Humans (less 

common 

symptoms) 

U.S. 

Outbreaks 

s

Bacteria Listeria monocytogenes No Domestic and 

wild animals 

Yes Listeriosis, 

meningoencephalitis, fever, and abortion 

Foodborne N

Bacteria Mycobacterium avium

complex (MAC) and ssp. Paratuberculosis (MAP)

Yes (generally in environment) 

Possibly sheep, cattle, goats, and birds 

Yes Respiratory 

infection, fever, and Crohn’s disease 

No recreational waterborne reported 

Pim

Bacteria Pseudomonas Yes None NA Dermatitis Recreational N

(generally in environment) 

waterborne 

Bacteria Salmonella Yes Poultry, swine, 

cattle, rodents, wild birds, turtles, dogs, and cats 

Yes Gastroenteritis 

(enteric fever and septicemia) 

Mainly foodborne and drinking water 

Im

Bacteria Serratia Yes 

(generally in environment) 

None NA Opportunisitic 

infection (cystitis) 

Hospital settings 

N

Bacteria Shigella Yes None (except 

primate colonies) 

NA Shigellosis, acute 

gastroenteritis, dysentary, fever, nausea, vomiting, and cramps 

Recreational and drinking water 

N

Bacteria Staphylococcus Yes Skin of warmblooded hosts Yes Cellulitis, pustules, boil, carbuncles, 

and impetigo (diarrhea and vomiting) 

Hospital settings, pools, and spas 

N
U.S. Environmental Protection Agency

February 2009 A-6 

Type Pathogen Waterborne Zoonotic Host

Zoonotic 

Host is 

Warmblooded 

Illnesses and Symptoms in 

Humans (less 

common 

symptoms) 

U.S. 

Outbreaks 

s

Bacteria Vibrio cholerae Yes Copepods, 

zooplankton 

No Profuse, watery 

diarrhea; vomiting 

None recently 

N

Bacteria Vibrio parahaemolyticus Yes 

(generally in environment) 

Molluscan shellfish 

No Acute 

gastroenteritis (septicemia) 

Foodborne N

Bacteria Yersinia Yes Pigs Yes Yersiniosis; acute, 

febrile diarrhea 

Mainly foodborne 

Pim

Protozoa Acanthamoeba Yes (freeliving) None NA Granulomatus ameobic 

encephalitis 

None reported 

N

Protozoa Ascaris lumbricoides Yes None NA Ascariasis and 

roundworm infection 

Foodborne N

Protozoa Balamuthia mandrillaris Yes (freeliving) Primates, sheep, dogs, 

and horses 

Yes Granulomatus 

ameobic encephalitis 

None reported 

N

Protozoa Balantidium coli Yes Primates 

pigs 

and Yes Severe dysentery None 

reported 

N

Protozoa Blastocystis hominis Yes Primates, 

cattle, sheep, pigs, horses, dogs, chickens, wild birds, alpacas, llamas, koalas, and wombats 

Yes Diarrhea, cramps, 

nausea, fever, vomiting, and abdominal pain 

None reported 

N
U.S. Environmental Protection Agency

February 2009 A-7 

Type Pathogen Waterborne Zoonotic Host

Zoonotic 

Host is 

Warmblooded 

Illnesses and Symptoms in 

Humans (less 

common 

symptoms) 

U.S. 

Outbreaks 

s

Protozoa Cryptosporidium parvum 

and Cryptosporidium hominis 

Yes Cattle, sheep, 

goats, pigs, horses, cats, dogs, wild animals, birds, reptiles, and fish 

Yes Cryptosporidiosis, 

profuse watery diarrhea, malaise, fever, anorexia, nausea, and vomiting 

Recreational and drinking water 

Im

Protozoa Cyclospora cayetanensis Yes None NA Watery diarrhea, 

malaise, fever, anorexia, nausea, and vomiting 

Foodborne and waterborne (drinking water and recreational water) 

N

Protozoa Entamoeba histolytica Yes Potentially 

primates, dogs, cats, pigs, rats, and possibly cattle 

Yes Amoebiasis, 

dysentery, and diarrhea 

None recently 

N

Protozoa Giardia intestinalis (also 

known as G. duodenalis and G. lamblia)

Yes Beavers, cats, 

lemurs, sheep, calves, dogs, foxes, chinchillas, alpacas, horses, pigs, cows, and muskrats 

Yes Giardiasis; diarrhea 

(chronic); steatorrhea; abdominal cramps; bloating; frequent loose, pale, greasy stools; fatigue; and malabsorption 

Recreational and drinking water 

Im
U.S. Environmental Protection Agency

February 2009 A-8 

Type Pathogen Waterborne Zoonotic Host

Zoonotic 

Host is 

Warmblooded 

Illnesses and Symptoms in 

Humans (less 

common 

symptoms) 

U.S. 

Outbreaks 

s

Protozoa Isosprora belli Yes None NA Foul smelling, 

foaming diarrhea (months to years), abdominal colic, and fever 

None reported 

N

Protozoa Microsporidia 

(Enterocytozoon bieneusi, Encephalitozoon cuniculi, E. intestinalis) 

Yes Cattle, pigs, 

cats, rabbits, and sheep 

Yes Diarrhea None 

reported 

Pim

Protozoa Naegleria fowleri Yes (freeliving) None NA Primary amebic meningoencephaliti

s 

Mainly ambient recreational 

N

waters 

Virus Adenoviruses Yes None NA Acute 

gastroenteritis and respiratory disease 

Waterborne N

Virus Astroviruses Yes None NA Gastroenteritis Waterborne N

Virus Avian influenza (H5N1) Unknown Birds Yes Mild upper 

respiratory illness to severe pneumonia and multiple organ failure 

None reported 

N
U.S. Environmental Protection Agency

February 2009 A-9 

Type Pathogen Waterborne Zoonotic Host

Zoonotic 

Host is 

Warmblooded 

Illnesses and Symptoms in 

Humans (less 

common 

symptoms) 

U.S. 

Outbreaks 

s

Virus Coronaviruses (e.g., 

severe acute respiratory syndrome (SARS)-CoV) 

Potentially (aerosolized wastewater) 

Possibly civets 

and other wild animals 

NA Fever, dry cough, 

dyspnoea, and myalgia (diarrhea) 

None reported 

N

Virus Enteroviruses 

coxsackie) 

(e.g., Yes None NA Gastroenteritis, 

exanthema, diarrhea, fever, pharyngeal lesions, myocarditis, respiratory disease, and pneumonia 

Recreational and drinking water 

N

Virus Hendra virus Unknown Horses Yes Severe respiratory 

disease and meningoencephalitis 

None reported 

N

Virus Hepatitis A virus Yes None NA Hepatitis - acute 

inflammation of the liver 

None recently 

N

Virus Hepatitis E virus Yes Possibly pigs, 

chickens, and 

rats (close viral 

relatives to human form) 

NA Hepatitis - acute 

inflammation of the liver (fatality in pregnant women) 

Rare in United States (common in other countries) 

N

Virus Human caliciviruses 

(norovirus, sapovirus) 

Yes None NA Diarrhea and 

vomiting 

Very common (waterborne 

and 

N

foodborne) 

Virus Nipah virus Unknown Pigs, bats, and 

flying foxes 

Yes Acute and febrile 

encephalitis 

None reported 

N
U.S. Environmental Protection Agency

February 2009 A-10 

Type Pathogen Waterborne Zoonotic Host

Zoonotic 

Host is 

Warmblooded 

Illnesses and Symptoms in 

Humans (less 

common 

symptoms) 

U.S. 

Outbreaks 

s

Virus Parechoviruses Yes None NA Pericarditis, 

herpangina, and respiratory disease 

None reported (probably occurs, but unidentified) 

N

Virus Reoviruses Yes None NA Mostly mild or 

subclinical (rarely biliary atresia, juvenile onset diabetes, fever, rash, respiratory disease, and diarrhea 

None reported (probably occurs, but unidentified) 

N

Virus Rotaviruses Yes None NA Diarrhea Very 

common waterborne 

N

Helminths Ancylostoma braziliense Mainly soil Dogs or cats Yes Larval migration 

leads to creeping eruption 

None reported (most important hookworm in 

N

humans - soil route) 

Helminths Angiostrongylus Yes Mollusks No Meningitis None 

reported 

N

Helminths Ascaris lumbricoides Mainly soil 

(drinking water possible) 

None NA Ascaris pneumonia 

(lung hemorrhage) 

None reported 

N
U.S. Environmental Protection Agency

February 2009 A-11 

Type Pathogen Waterborne Zoonotic Host

Zoonotic 

Host is 

Warmblooded 

Illnesses and Symptoms in 

Humans (less 

common 

symptoms) 

U.S. 

Outbreaks 

s

Helminths Ascaris suum Mainly soil Pigs Yes Ascaris pneumonia 

(lung hemorrhage) 

None reported 

N

Helminths avian schistosomes 

(includes S. mansonni) 

Yes Snails (birds 

are infected but not 

Yes Cercarial dermatitis 

(swimmer’s itch) 

None reported 

Lim

sources) 

Helminths Baylisascaris procyonis Mainly soil Raccoons Yes Larval migration 

may damage to the visceral and ocular 

None reported 

N

systems (migration to brain) 

Helminths Dracunculus medinensis Yes Crustaceans No Connective tissue None N

migration, emerging in lower limb blister 

reported 

Helminths Echinococcus Yes Foxes, dogs Yes Cystic hydatid 

disease, alveolar hydatid disease, polycystic hydatid disease, and polycystic hydatid disease 

None reported 

Lim

Helminths Fasciola hepatica Yes Snails 

(herbivores and humans 

Yes Fascioliasis None 

reported 

Lim

infected) 

Helminths Pseudophyllid cestodes Yes Copepods, fish No Cutaneous or 

mucocutaneous invasion 

None reported 

N
U.S. Environmental Protection Agency

February 2009 A-12 

Type Pathogen Waterborne Zoonotic Host

Zoonotic 

Host is 

Warmblooded 

Illnesses and Symptoms in 

Humans (less 

common 

symptoms) 

U.S. 

Outbreaks 

s

Helminths Schistosomes Yes Snails (many 

animals can be infected, but are not sources) 

No Schistosomiasis 

(chronic infection - liver fibrosis, portal hypertension) 

None reported 

N

Helminths Strongyloides Mainly soil Dogs Yes Eosinophilia None 

reported 

N

Helminths Taenia solium (pork 

tapeworm)

Yes Pigs Yes Cysticercosis and 

myositis 

None reported 

Lim

Helminths Toxocara canis Yes Dogs Yes Toxocariasis (larval 

migration leads to hemorrhage and granulomatous lesions in the 

None reported 

Lim

central nervous system) 

Helminths Toxocara cati Yes Cats Yes Toxocariasis (larval 

migration leads to hemorrhage and granulomatous lesions in the 

None reported 

Lim

central nervous system) 
U.S. Environmental Protection Agency

February 2009 A-13 

Type Pathogen Waterborne Zoonotic Host

Zoonotic 

Host is 

Warmblooded 

Illnesses and Symptoms in 

Humans (less 

common 

symptoms) 

U.S. 

Outbreaks 

s

Helminths Toxoplasma gondii Yes Cats Yes Toxoplasmosis, (in 

fetally exposed children - mental 

None reported in recreational 

Pim

retardation, loss of vision, hearing impairment, and mortality) 

water 

Helminths Trichinella spiralis Mainly soil Variety of 

animals 

Yes Trichinosis Foodborne 

(mainly consumption of 

N

undercooked pork) 

Helminths Trichuris trichiuria Mainly soil Monkeys, pigs, 

dogs, cats, and chicken 

Yes Trichuris dysentary 

syndrome, chronic diarrhea, anemia, and growth retardation 

Foodborne N

Prion Bovine Spongiform 

Encephalopathy (BSE) 

Unknown Cattle Yes Variant CreutzfeldtJakob disease Foodborne N

NA = Not applicable 
U.S. Environmental Protection Agency

February 2009 B-1 

APPENDIX B 

LITERATURE SEARCH STRATEGY AND RESULTS

The literature search strategy consisted of a number of combined approaches. Search terms and 

a synopsis of information needed were given to a professional librarian to search the online 

DIALOG databases. To supplement the DIALOG searches, individual authors used free search 

engines on the internet to find articles pertaining to specific information needed. Experts that 

participated in EPA’s Experts Scientific Workshop on Critical Research Needs for the 

Development of New or Revised Recreational Water Quality Criteria11 were contacted by email 

and requested to contribute literature they felt was important. The titles of literature cited in 

specific reports, books, review articles, and conference proceedings were evaluated for 

relevance. 

B.1 Initial Literature Search Strategy Conducted by Professional Librarian 

Selection of DIALOG data base files used for this search: 

 File 155:MEDLINE(R) 1950-2007/Nov 30 

 (c) format only 2007 Dialog 

 File 266:FEDRIP 2007/Sep 

 Comp & dist by NTIS, Intl Copyright All Rights Res 

 File 144:Pascal 1973-2007/Nov W3 

 (c) 2007 INIST/CNRS 

 File 110:WasteInfo 1974-2002/Jul 

 (c) 2002 AEA Techn Env. 

 File 245:WATERNET(TM) 1971-2007Jul 

 (c) 2007 American Water Works Association 

 File 117:Water Resources Abstracts 1966-2007/Aug 

 (c) 2007 CSA. 

 File 5:Biosis Previews(R) 1926-2007/Nov W4 

 (c) 2007 The Thomson Corporation 

 File 40:Enviroline(R) 1975-2007/Oct 

 (c) 2007 Congressional Information Service 

 File 143:Biol. & Agric. Index 1983-2007/Oct 

 (c) 2007 The HW Wilson Co 

 File 6:NTIS 1964-2007/Dec W3 

 (c) 2007 NTIS, Intl Cpyrght All Rights Res 

 File 72:EMBASE 1993-2007/Dec 04 

 (c) 2007 Elsevier B.V. 

Main search strategy used for this search: 

Fecal set AND Composition set AND (Pathogen or Waterborne sets): 1985-present

S1 240528 FECAL OR FECES OR FAECAL OR FAECES OR DUNG OR SCAT OR EXCREMENT 

 OR MANURE OR STOOLS) 

S2 1686966 COMPOSITION OR COMPOSED OR ANIMAL(1N)HUMAN()(TRANSMISSION OR 

 CONTAMINATION) 

 11 Report from this workshop: http://www.epa.gov/waterscience/criteria/recreation/. 
U.S. Environmental Protection Agency

February 2009 B-2 

S3 3842348 PATHOGEN? ? OR INDICATOR? ? OR RISK OR RISKS 

S4 983 WATERBORNE()(PATHOGEN? ? OR ZOONO? OR ILLNESS?) 

S6 1140 S1 AND S2 AND (S3 OR S4) 

S719961011 PY=1920:1984 

S8 1037 S6 NOT S7 (limited to 1985-present; foreign language OK) 

S9 704 RD S8 (unique items, deduped) 

Dates: 1985-present 

Language: No restrictions 

Retrieve: Titles and year 

Format: MS Word 

Interested in international and domestic journals and government reports. 

Descriptions of these files are available at http://library.dialog.com/bluesheets/. 

Search terms:

Waterborne pathogen* 

Waterborne illness* 

Waterborne zoon* 

Emerging waterborne zoonotic pathogen* 

Antibiotic resistan* AND zoonotic pathogen* 

Transmission rate waterborne pathogen* 

Evolution zoon* pathogen* 

Human fecal composition micro* 

Enterohemorrhagic E. coli symptoms 

Salmonella symptoms 

Shigella symptoms 

Campylobacter symptoms 

Listeria symptoms 

Cryptosporidium symptoms 

Giardia symptoms 

norovirus symptoms 

rotavirus symptoms 

hepatitis E symptoms 

waterborne dermal infection* 

waterborne eye infection* 

waterborne ear infection* 

waterborne respiratory infection* 

What we want from the literature search:

• Fecal composition of species that harbor zoonotic pathogens (species of livestock and 

wild animals 

• Fecal composition of humans – pathogens and indicators 

• The extent to which strains found in animals can be transmitted to humans 
U.S. Environmental Protection Agency

February 2009 B-3 

• An evaluation of the extent to which the information identified can be used to support the 

differentiation of risk from animal and human sources of fecal contamination 

• Which organisms are of substantial public health concern that occur in ambient waters 

and are pathogenic to humans 

• Which of these organisms are also present in animal populations 

• The extent to which these organisms found in animals can be transmitted to humans 

• The potential outcomes of human infection and disease from animal sources 

• Specific pathogens: E. coli O157-H7, Salmonella, Shigella, Campylobacter, Listeria, 

Cryptosporidium, Giardia, norovirus, rotavirus, Hepatitis E, emerging pathogens. For 

each: 

o Describe illness symptoms (range asymptomatic to severe) 

o Describe route of exposure from recreational immersion in water including, 

inhalation, skin and mucus, eyes, ears 

o Incidence (morbidity and mortality data, through recent time) 

o Zoonotic potential – which animal species 

• Variations in strains that effect infectivity, severity of symptoms, environmental survival 

and treatability 

• Short summary review of emerging pathogen mechanisms (not too deep into molecular 

mechanisms of evolution) 

• Anything in the water matrix that affects survivability and infectivity, and virulence 

• Pathogen:indicator ratios 

B.2 Summary of Literature Search Results

This process resulted in a total order of 535 documents (primarily peer reviewed scientific 

articles), of which a total of 332 (62 percent) were received during the expedited writing process, 

not all of which could be reviewed. There are many more papers in the peer-reviewed literature, 

and this by no means represents all of them. 319 citations were included in the white paper. 

B.3 Supplemental Free Online Search Engines 

The following terms were searched on Google (http://www.google.com/): 

Search Topic Approximate # Titles 

Reviewed # Titles of Interest 

E. coli + deer 10 1 

Adenoviruses + zoonotic 30 3 

Hepatitis E+ condition + symptoms 30 2 

Rotavirus + illness + symptoms 20 1 
U.S. Environmental Protection Agency

February 2009 B-4 

The following terms were searched on Google Scholar (http://scholar.google.com/): 

Search Topic Approximate # Titles 

Reviewed # Titles of Interest 

Adenoviruses + zoonotic 10 1 

Rotavirus + illness + symptoms 30 3 

Giardiasis + swimming 200 5 

Giardiasis + surveillance 200 3 

Giardia + symptoms 100 5 

Giardia + cyst 100 2 

Giardia + beach 200 1 

Cryptosporidium + hominis 100 1 

Cryptosporidium + beach 150 1 

Cryptosporidium + incidental ingestion 250 4 

Cryptosporidium + review 100 2 

Cryptosporidium + exposure factors 150 3 

Cryptosporidium + exposure 50 2 

Cryptosporidium + symptoms 50 3 

Cryptosporidium + risk 50 0 

Campylobacter + chronic 50 3 

Campylobacter + illness 50 3 

Campylobacter + infection 50 4 

Campylobacter + symptoms 50 1 

Campylobacter + water 15 2 

Campylobacter + pathogenesis 5 1 

Salmonella + transmission 20 8 

Salmonella + transmission in water 11 2 

Salmonella + antibiotic resistance 20 3 

Salmonella + pathogenesis 3 1 

Shigella + outbreak 23 4 

Shigellosis 35 4 

The following terms were searched on PubMed (http://www.ncbi.nlm.nih.gov/sites/entrez): 

Search Topic # Titles Reviewed # Titles of Interest 

E. coli O157:H7 + survival + environment 204 23 

Salmonella + survival + environment 376 4 

Shigella + survival + environment 65 10 

Campylobacter + survival + environment 57 17 

Norwalk Virus + survival + environment 2 Yes 

Rotavirus + survival + environment 54 17 

Hepatitis E + survival + environment 3 Yes 
U.S. Environmental Protection Agency

February 2009 B-5 

The following terms were searched on Scirus (http://www.scirus.com/): 

Search Topic Approximate # Titles 

Reviewed # Titles of Interest 

Helicobacter + environmental survival 30 1 

Leptospira + CID 10 1 

Leptospira + environmental survival 30 2 

Leptosporidiosis + symptoms 30 0 

The following terms were searched on the CDC website (http://www.cdc.gov/): 

Search Topic Approximate # Titles 

Reviewed # Titles of Interest 

Legionella + EID 10 1 

Leptospira + EID 10 1 

Avian influenza + EID 10 1 

H5N1 + EID 20 0 

SARS + EID 30 2 

Hendra virus + EID 20 0 

Nipah virus + EID 20 2 

Strongyloides + EID 10 1 

BSE + EID 10 1 

B.4 Experts Contacted 

The flowing experts in the field were contacted directly by email and asked to suggest 

references: 

Nicholas Ashbolt, USEPA 

Thomas Atherholt, New Jersey Department of Environmental Protection 

Michael Beach, Centers for Disease Control and Prevention 

Bart Bibler, Florida Department of Health 

Alexandria Boehm, Stanford University, California 

Rebecca Calderon, USEPA 

Jennifer Clancy, Clancy Environmental Consultants 

Jack Colford, University of California, Berkeley 

Elizabeth Doyle, USEPA 

Alfred Dufour, USEPA 

Lee Dunbar, Connecticut Department of Environmental Protection 

Lora Fleming, University of Miami School of Medicine and Rosenstiel School of Marine and 

Atmospheric Sciences, Florida 

Charles Hagedorn, Virginia Tech 

Joel Hansel, USEPA 
U.S. Environmental Protection Agency

February 2009 B-6 

Lawrence Honeybourne, Orange County Health Care Agency, Santa Ana, California 

Donna Francy, U.S. Geological Survey 

Roger Fujioka, University of Hawaii, Manoa 

Toni Glymph, Wisconsin Department of Natural Resources 

Mark Gold, Heal the Bay, California 

Paul Hunter, University of East Anglia, U.K. 

Dennis Juranek, Centers for Disease Control and Prevention (retired) 

David Kay, University of Wales, U.K. 

Sharon Kluender, Wisconsin State Laboratory of Hygiene 

Erin Lipp, University of Georgia 

Graham McBride, National Institute of Water and Atmospheric Research, New Zealand 

Charles McGee, Orange County Sanitation District, California 

Samuel Myoda, Delaware Department of Natural Resources 

Charles Noss, USEPA 

Robin Oshiro, USEPA 

James Pendergast, USEPA 

Mark Pfister, Lake County Health Department, Illinois 

John Ravenscroft, USEPA 

Stephen Schaub, USEPA 

Mark Sobsey, University of North Carolina, Chapel Hill 

Jeffrey Soller, Soller Environmental, California 

Michael Tate, Kansas Department of Health and Environment 

Peter Teunis, RIVM (National Institute of Public Health and the Environment), Netherlands 

Gary Toranzos, University of Puerto Rico, Rio Piedras 

Timothy Wade, USEPA 

John Wathen, USEPA 

Stephen Weisberg, Southern California Coastal Water Research Project 

David Whiting, Florida Department of Environmental Protection 

Richard Zepp, USEPA 

B.4 Previously Cited References 

The following specific reports were obtained and the titles of the references cited in the reports 

were reviewed for relevance: 

• NRC. (2004) Indicators for Waterborne Pathogens. The National Academies Press 

• USEPA. (2007) Report of the Experts Scientific Workshop on Critical Research Needs 

for the Development of New or Revised Recreational Water Quality Criteria 

http://www.epa.gov/waterscience/criteria/recreation

• WHO. (2004) Waterborne Zoonoses. http://www.who.int/water_sanitation_health/

diseases/zoonoses.pdf

• References cited by the Natural Resources Defense Council reviewers of the EPA Critical 

Path Science Plan 

• USEPA Internal draft Adenovirus criteria document 

• USEPA Internal draft pathogenic E. coli criteria document 
U.S. Environmental Protection Agency

February 2009 B-7 

• Boehm et al. (2008) A sea change ahead for recreational water quality criteria. (peer 

review in progress) 

In addition, Clancy Environmental Consultants, Inc., ICF International, Soller Environmental, 

WaltJay Consulting, and EPA’s Health and Ecological Criteria Division all maintain extensive 

literature databases and reference lists from previously completed projects. All of those in house 

resources were also sources of literature. 
U.S. Environmental Protection Agency

February 2009 C-1 

APPENDIX C 

INCIDENTAL INGESTION OF AMBIENT WATER DURING 

RECREATIONAL ACTIVITIES

There is a paucity of data concerning rates of incidental ingestion of surface water during 

recreational activities. Most of the available estimates address exposures during swimming in 

swimming pools, which may not necessarily be representative of typical “incidental” exposures 

in ambient waters. Dufour et al. (2006) reviewed early estimates of swimming-related water 

ingestion and concluded that incidental ingestion ranged from 10 to 50 mL per hour. None of the 

early estimates, however, were based on actual studies of water ingestion. EPA’s Risk 

Assessment Guidance for Superfund (USEPA, 1989) recommended a value of 50 mL per hour 

for ingestion during water recreation, citing an early version of EPA’s Exposure Factors 

Handbook (EFH). The latest version of the EFH (USEPA, 1997) contains no recommendation 

concerning recreational water intake. Hammond et al. (1986), in their assessment of the 

potential toxicity of swimming pool disinfectants, estimated that a 70-kg adult might ingest “1 to 

2 cups” of water, meaning approximately 500 mL. However, this is a “ballpark” estimate and is 

not supported by observational data. 

Allen et al. (1982) estimated water ingestion by competitive swimmers by measuring urinary 

excretion of isocyanuric acid, an unmetabolized compound used to stabilize chlorine levels in 

swimming pools. The average estimated water intake among the five swimmers that were 

studied was 161 mL per hour. The investigators also determined that (1) essentially all of the 

ingested isocyanuric acid appeared in urine within 24 hours, thus negating concern for 

elimination by other pathways; and (2) dermal absorption of the tracer compound was 

insignificant compared to the ingestion intake. 

Using methods similar to those used by Allen et al. (1982), Dufour et al. (2006) estimated water 

intake in 12 adults and 41 “nonadults” engaged in less vigorous water recreation at a community 

swimming pool. Based on the amounts of isocyanurate excreted in urine, they estimated that 45 

minutes of water recreation resulted in average water intakes of 37 mL (49 mL/hr) for nonadults 

and 16 mL (21 mL/hr) for adults. The exposures measured by Dufour et al. (2006) are perhaps 

more likely to be representative of typical “incidental” exposures than those of the competitive 

swimmers measured by Allen et al. (1982), suggesting the lower values may provide a better 

basis for estimating incidental exposures. 

A larger follow-up study of 549 participants was subsequently conducted at several public and 

private outdoor swimming pools (Evans et al., 2006). Participants were requested to engage in 

active swimming for between 45 and 60 minutes. The overall average incidental ingestion rate 

was 32 mL/hr, with a range of 1 to 280 mL/hr. Adults averaged 24 mL/hr, and children averaged 

47 mL/hr. Children (ages not specified) swallowed approximately twice as much water as 

adults. The follow-up study also showed that males ingested more than females and that adult 

men ingested more than adult women. 
U.S. Environmental Protection Agency

February 2009 C-2 

The small number of studies that are available measured water intake in only a few subjects and 

characterized water ingestion during either very active swimming or poorly defined water 

recreational activities. In addition, the incidental ingestion data that are available are for “clean” 

pool water and may not represent incidental ingestion for surface waters, which may provoke 

stronger avoidance behaviors due to the perception that surface waters are nonpotable.