|
|
February 10-12, 1999, M/DBP Stage 2 FACA: Health Effects Workshop
|
ISSI Consulting Group 8455 Colesville Road Suite 915 Silver Spring, MD 20910 Contract: 68-C-98-195 |
RESOLVE 1255 23rd Street, NW Suite 275 Washington, DC 20037 EPA Contract No. 68-W4-0001 Work Assignment No. 195 |
CONTENTS
DBP Health Effects: Reproductive and Developmental Risks
Microbial: Background for Long Term 2 Enhanced Surface Water Treatment Rule
ATTACHMENTS
(Note: attachments not included in web version.)
I.A | Meeting Agenda: Health Effects Stakeholder Meeting for the Stage 2 DBPR and LT2ESWTR |
I.B | List of meeting participants. |
I.C | Bio of Presenters. |
II.A | History of Stage 1 Rules & Regulatory Needs for Stage 2 M/DBP Rules - Stig Regli, EPA |
II.B | Overview of DBP Formation and Occurrence - Stuart W. Krasner, Metropolitan Water District of Southern California |
II.C | Overview of Types of Health Effects Data and How Data are Used in Decision Making - Jeanette Wiltse, EPA |
II.D | Improving Exposure Assessments in Epidemiological Studies of DBPs - J.R. Nuckols, Colorado State University |
III.A | Epidemiological Studies of DBPs and Cancer - Michael McGeehin, CDC |
III.B | Epidemiological Research and Approaches on DBP Cancer Endpoints - Terry Harvey, EPA |
III.C | Case-Control Study in Ontario, Canada: Examining the Association Between Cancer and Exposure to Chlorinated Byproducts - Will King, Health Canada |
III.D | Case-Control Studies in Iowa and Maryland: Examining the Association Between Cancer and Exposure to Chlorination Byproducts - Kenneth Cantor, National Cancer Institute |
III.E | Toxicology of Individual DBPs: Overview of Current Science and Current and Future Research and Schedules for Completion - Fred Hauchman, EPA |
III.F | Research Evaluating the Toxicity of Bromate, Chlorate, and Haloacetic Acids - Doug Wolf, EPA |
III.G | Research Evaluating the Toxicity of Bromodichloromethane - Rex A. Pegram, EPA |
III.H | Research on the Risk Assessment of Mixtures of Disinfection By-Products (DBPs) in Drinking Water - Linda Teuschler, EPA |
III.I | Environmental Health Criteria Monograph for Disinfectants and Disinfectant By-Products, Summary and Conclusions of IPCS Task Group, Geneva 17-21, August 1998 -Hend Galal-Gorchev, World Health Organization (WHO) retired |
III.J | DBP Risk Management: Technology-Based Occurrence Issues - Phillippe Daniel, Camp Dresser & McKee, Inc. |
IV.A | Reproductive and Developmental Effects of Exposure to DBPs: An Overview of Epidemiological Data - John Reif, Colorado State University |
IV.B | Health Effects: Reproductive and Developmental Epidemiology: Current and Future Research - Rebecca Calderon, EPA |
IV.C | California Studies: Trihalomethanes in drinking water and Spontaneous Abortion - Kirsten Waller, Sequoia Foundation |
IV.D | CDC/EPA Birth Defect Studies - Michele Lynberg, CDC-NCEH |
IV.E | New Jersey Studies: Presentation Materials & A Case Control Study of Neural Tube Defects and Drinking Water Contaminants - Judith Klotz, NJDPH |
IV.F | Toxicology Reproductive: Overview of Current Science and Current and Future Research and Schedules for Completion - Gary Klinefelter, EPA |
IV.G | Toxicology Developmental: Overview of Current Science and Current and Future Research and Schedules for Completion - Sid Hunter, EPA |
IV.H | Microbials and Disinfection ByProducts - December 1998, AWWA Research Foundation Report. |
V.A |
- Mark LeChevallier, American Water Works Service Company |
V.B | Overview of Types of Health Effects Data (Microbes) and How Data is Used in Decision Making - Stig Regli, EPA |
V.C | Epidemiology: Overview of Current Science Including Sensitive Subpopulations - Dennis Juraneck & Deborah Levy, CDC |
V.D | Microbial Pathogens and Epidemiology: Current and Future Research and Schedules for Completion - Rebecca Calderon, EPA |
V.E | Epidemiology: The Use of Serology to Study Prevalence of Cryptosporidiosis Due to Drinking Water - Jeff Griffiths, Tufts University |
V.F | Time Series Studies on GI Illnesses Related to Turbidity - Bob Morris, Tufts University |
V.G | Dose-Response: Overview of Current Science - Charles Haas, Drexel University |
V.H | Cryptosporidium parvum Volunteer Study - Cynthia Chappell, University of Texas-Houston |
V.I |
V.I Determination of Norwalk Virus Dose-Response in Human Volunteers - Christine Moe, University of North Carolina |
Welcome and Introduction
On February 10-12, 1999 the U.S. EPA held the Stage 2 Microbial/Disinfectant Byproducts (M/DBP) Health Effects Workshop. Cynthia Dougherty, Director, Office of Ground Water and Drinking Water, opened the meeting by welcoming the guests and reviewing the purpose of the workshop. [See Attachment I.A for meeting agenda, Attachment I.B for list of meeting participants and Attachment I.C for list of speakers and bios.] The purposes of this Workshop are to provide participants with:
The objective of this meeting is to focus on research, not to decide its meaning in the regulatory context, but to share the state of the science. This is the second in a series of three public workshops to review scientific issues surrounding the Stage 2 Disinfection Byproduct (DBP2) and Long Term 2 Enhanced Surface Water Treatment (LT2) rules. The first was the Statistics Workshop held November 19, 1998.(1) A third public meeting is the March 10-12, 1999 - ICR, Treatment, and Methods Research Workshop to discuss occurrence and treatment.(2)
1 The Final Meeting Summary and Attachments for the November 19, 1998 Statistics Workshop are available by contacting Detra Stoddard at RESOLVE at [dstoddard@resolv.org] or (202) 965-6218. 2 The ICR Workshop Meeting summary, when complete, will be available by contacting Detra Stoddard. |
Dorothy Patton, EPA/ORD, presented the three key aspects of the Health Effects Meeting: (1) the health effects discussion and the many aspects that allow a comprehensive look at the spectrum of available research and information, (2) the collaboration of many organizations, and (3) discussions for how to proceed in the future.
This meeting summary presents a short summary of the presentations and discussions that occurred at the workshop. Attachments include presentation materials and other more detailed background and supporting information. RESOLVE would like to acknowledge the technical support provided by ISSI, Inc., funded by EPA OST/OW, to produce the February and March M/DBP Stakeholder meeting summaries.
Background
History of Stage 1 Rules and Regulation
Stig Regli, EPA, presented the history and overview of the Stage 1 Disinfection Byproducts and Interim Enhanced Surface Water Treatment rules, baseline risk for the final Stage 1 rules and the timeline and major regulatory questions that need to be addressed for the Stage 2 rules [Attachment II.A].
In 1994, participants in the Stage 1 FACA discussions agreed to wait for more health effects and risk information to become available before developing the Stage 2 regulations. A commitment was made by the drinking water industry and EPA through the Information Collection Rule (ICR) to collect more information on occurrence and treatment for pathogens and by-products. There was also a recognized need for more research, and as a result, research funding was increased.
The Stage 1 rule was promulgated in 1998. A broad range of possible cancer risk reduction was assumed for the Stage 1 rule. While quantification of actual risk reduction was highly controversial, EPA assumed a risk reduction of 25% considering reductions in exposure from TTHMs as a surrogate for DBPs in general. For noncancer risk, there was not enough information and the Regulatory Impact Assessment prepared by EPA did not quantify this risk.
The following questions are important to be answered during Stage 2 Rule development:
- What is the risk from brominated DBPs versus non-bromide DBPs?
The time line for the Stage 2 rules was proposed by EPA: 1) Rule development - Spring 1999-Spring 2000 and 2) Rule proposal - early Spring 2001. In response to a question on how Stage 2 FACA can begin discussions before relevant data may become available, Regli explained that the rule could be proposed with two or more alternatives which are followed depending on the findings of the new information (e.g., if outcome A, then rule A; If outcome B, then rule B). A Notice of Data Availability (NODA) in summer 2000 could describe such new information and regulatory consequences.
Overview of DBP Formation and Occurrence
Stuart W. Krasner, Metropolitan Water District of Southern California, presented an overview of DBP formation and occurrence including; current industry disinfection practices, DBP chemistry and the major factors that effect DBP formation, and the occurrence of DBPs from the use of different disinfectants [Attachment II.B].
Disinfectant is added at the beginning of the plant for multiple reasons; primarily for microbial inactivation, but also to prevent algal growth, for taste-and-odor control, and for inorganic oxidation. As a result of the Stage 1 DBP rules, chlorine dioxide, and ozone are being used more frequently for primary disinfection and chloramines for secondary disinfection and to maintain residual.
DBPs are formed when disinfectants react with precursors such as natural organic matter (NOM) and bromide in water. NOM comes from decaying vegetation, etc. and bromide comes from salt water intrusion into source waters, etc. All disinfectants form DBPs. DBPs are formed in one of two reactions: 1) Halogen substitution reactions resulting in halogenated by-products and 2) oxidation reactions. Secondary by-products are also formed when multiple disinfectants are used.
Temperature, time and pH, along with the disinfection process and other source water characteristics, determine what DBPs will be formed. Most reactions that form DBPs occur in the first 24 hours. The pH determines, in part, which DBP will be formed, resulting in risk/risk tradeoffs. For example, lowering pH to control for trihalomethane (THM) formation can result in the increased formation of trihaloacetic acids. Reaction time is also an important variable - for example, chloral hydrate is unstable at high pH levels, and over time, it degrades to chloroform, which results in an increase of THMs over time.
Bromide also presents risk/risk tradeoff questions: an increase in bromide in source water results in less formation of chloroform and a greater formation of bromodichloromethane. Moderate-to-high bromide levels increase the formation of bromoform. Increased bromide levels result in higher levels of brominated DBP species. Regulations are currently based on total THM instead of individual THMs.
The following points were discussed by participants:
Overview of Types of Health Effects Data and How Data are Used in Decision Making
Jeanette Wiltse, EPA, presented an overview of the role of health effects data in EPA's decision making process [Attachment II.C]. Wiltse described two distinct domains of risk assessment and risk management, and presented a summary of the risk assessment paradigm and information EPA uses in assessing risks from DBPs. The risk assessment paradigm consist of: 1) Hazard Index, 2) Dose Response, 3) Exposure Assessment, and 4) Risk Characterization.
Health endpoints considered in a Risk Assessment are cancer (natural disease common to differentiated organisms) and non cancer (acute and chronic). Non-cancer effects include organ effects, reproductive effects, developmental effects, neurotoxic effects and other systemic effects (does the animal lose weight, etc.). It has been difficult to look at mixtures of DBPs, and research is now being developed to do animal testing with mixtures.
The advantages of human data over animal data were discussed. Human data are clear, but there are the issues of cost and ethics. Animal data are clear empirically, but extrapolating the data to humans is difficult.
In response to a question, Wiltse stated that the terms "linearity" and "threshold" should not be interchanged. Threshold is intercept, whereas linearity is based upon the shape of the curve.
Improving Exposure Assessments in Epidemiology
Jay Nuckols, Colorado State University, presented an overview of exposure assessment in the context of epidemiological studies, the state of the science with respect to DBPs, and issues in context with the Stage 2 rulemaking process [Attachment II.D].
Exposure means that a dose is reaching a target. Surrogates for exposure are used because they can be used quantitatively to predict exposure to a population or individual. Nuckols reviewed DBP studies and surrogates for exposure and emphasized that THMs have been used as a surrogate for exposure for all DBPs.
Two main types of epidemiology studies are: 1) Case-Control (contact participants to gather information) and 2) Ecological studies (those that get information indirectly).
The problems encountered in exposure assessment are:
Nuckols made the following points regarding epidemiological studies:
The following points were emphasized by participants concerning approaches for epidemiological studies:
DBP Health Effects: Cancer Risk
Epidemiology: Overview of Current Science
Michael McGeehin, CDC, discussed environmental epidemiology of DBPs and cancer [Attachment IIIA]. McGeehin defined epidemiology as the study of disease in a population. Environmental epidemiology is defined as the study of disease in population with environmental data.
Different types of epidemiological studies include: 1) Ecological studies, 2) Case-Control studies, and 3) Cohort studies. Ecological studies are studies that are put together on previously collected data, and are used to compare groups rather than individuals. Ecological studies are usually considered a good basis for a hypothesis. Case-Control studies are the most common type of study. Case-control studies are most useful for studying rare diseases. A problem with case control studies is recall bias. For example, persons with disease (cases) will look at exposure differently than people who have not had the disease (controls). Cohort studies are studies in which people with exposure are followed in time to see if they develop disease. There are also retrospective cohorts. A problem with cohort studies is that they are very expensive and time consuming.
Criteria for determining causation are: 1) strength of association (relative risk, odds ratio); 2) consistency of association; 3) biologic gradient; 4) biologic plausibility; and 5) temporally correct.
Results of epidemiological studies have shown evidence of moderate association between DBP exposure and bladder cancer, but no causality for bladder cancer. Population Attributable Risk (PAR) studies for colon cancer and for rectal cancer were inconclusive, however, for bladder cancer it was established that 2 to 17% of the disease would not occur if exposure were eliminated. Studies have shown a moderate association between DBP exposure and bladder cancer.
In response to a question, Nuckols explained that the exposure for the EPA PAR included the surrogate, chlorinated waters, and THMs. Exposure was underestimated in studies that did not detail the exposures.
Epidemiological Research and Approaches on DBP Cancer Endpoints
Terry Harvey, EPA, presented a brief overview of ten EPA human epidemiology research studies that will be carried out in FY 99 and 00) [Attachment III.B]. EPA Office of Research and Development's strategy for cancer epidemiology research is to:
Improve cancer risk estimates through a retrospective evaluation of exposure information in completed studies. Attempt will be made to connect animal toxicities to human responses. This will include DBP mixture issues. Harvey indicted that ORDs program for the use of public health approaches (like epidemiology for DBPs) is at a re-evaluation point and he encouraged collaborations on this issue.
In response to questions Harvey made the following points:
Case-Control Study in Ontario, Canada: Examining the Association Between Cancer and Exposure to Chlorinated Byproducts
Will King, Health Canada, reviewed the relationship between environmental factors and disease occurrence using a case control study to study DBPs and Bladder Cancer [Attachment III.C].
The study area was Ontario, which has 11.6 million residents, that live mostly along the Great Lakes:
The cases had bladder, colon and rectal cancer, with the cancer information coming from the cancer registry. The controls came from telephone marketing. Exposure assessment was determined using a questionnaire and a survey to water treatment facilities. This study focused on THMs. Different approaches to estimate levels of THM over time was done. A model was used to predict THM concentration from 30 years ago, since they were not measured.
Increased DBP exposure was correlated with bladder cancer. For colon cancer, an increased risk was not seen until there were higher levels of DBPs. Unlike bladder cancer, there is a difference in risk based on gender - greater in males for 35 - 40 years of exposure. There was no increase of risk for rectal cancer in men or women.
The probability of developing cancer by the age of 75 was discussed. For most individuals, developing bladder cancer is not a "huge" risk. Therefore, the extrapolation of risk to an individual as a probability of bladder cancer is not very high. However, studies have shown that about 38% of the population is exposed to increased levels of DBPs, and
suggests that 15% of bladder cancer in Ontario is attributable to DBPs-- 165 cases and 75 deaths.
King made the following points in response to questions from participants:
Case-Control Studies in Iowa and Maryland: Examining the Association Between Cancer and Exposure to Chlorination Byproducts
Kenneth Cantor, National Cancer Institute, presented the Iowa case-control study. The Maryland study is much more limited so was not included as originally planned [Attachment IIID]. Iowa was chosen as a location for this case control study for the following reasons: 1) a high quality cancer registry; 2) an adequately sized and cooperative population; 3) one-third of the population is on chlorinated surface, one-third of the population is on chlorinated ground water, one-third of the population is on non chlorinated water; 4) treated surface waters in Iowa historically had high byproduct levels.
Results of the study indicate: there was an association between the duration of exposure to chlorination byproducts and risk of rectal cancer among both sexes and risk of bladder and brain cancer among males. The association for bladder cancer with duration of byproduct exposure was also observed among smokers. There was an attempt to differentiate between effects among men and among smokers, but this was not possible in the context of this study. There was no excess risk for colon cancer with duration of chlorinated surface water use. Conclusions about brain cancer should not be drawn from this one study. Overall results of the study indicate that there is an association with bladder, rectum, and brain cancer in males, and rectum cancer in females, for exposure to THMs, used as a surrogate of exposure to the chlorination byproduct mixture.
Nitrate in water and a possible association with bladder cancer was not considered in this study. If nitrate is a risk factor for bladder cancer (not known at this time), it would likely act to depress the observed levels of association with chlorination byproducts. This is because nitrate is a larger problem in non-chlorinated private wells than in chlorinated surface waters, and people who consumed water from private wells were considered to be "unexposed" in this study.
Cantor made the following points in response to questions from participants:
Toxicology of Individual DBPs: Overview of Current Science and Current and Future Research and Schedules for Completion
Fred Hauchman, EPA, presented an overview of current and future research on toxicology for individual DBPs and schedules for completion [Attachment IIIE]. The two types of toxicology studies are: 1) chronic and subchronic bioassays in rodents; and 2) short and intermediate term studies, including those being done on transgenic mice, fish species (i.e. medaka), mammalian and non mammalian cells, and structure activity relationships.
Hauchman made the following points on the "state of science" on DBP toxicity:
Additional data needs include: modes of action data for risk assessment and carcinogenicity studies of selected brominated and chlorinated DBPs administered in drinking water. New studies are underway or planned to provide screening level data on the carcinogenicity, neurotoxicity and immunotoxicity of several DBPs (reproductive toxicity research is discussed elsewhere). There is not much information on the potential neurotoxicology and immunotoxicology of DBPs to determine if these effects are likely to be of public health concern. Data from the new long-term cancer studies will not be available for Stage 2, but pre-chronic data from these long-term studies on cancer hazard and mode of action data will be available.
EPA is devoting significant resources on DBP research in the coming years. The focus of the research will be developing hazard identification and dose-response information to support DBP risk assessments for the toxic endpoints described above.
Hauchman made the following points in response to questions from participants:
Research Evaluating the Toxicity of Bromate, Chlorate, and Haloacetic Acids
Doug Wolf, EPA, presented an overview of the toxicity and associated carcinogenicity of haloacetic acids, bromate, and chlorate and reviewed the collaborative work being conducted between the EPA and National Toxicology Program at NIEHS [Attachment IIIF].
The goals of this research are to identify key events, determine dose-response relationships to key events, and provide data that would indicate which risk characterization approach is most relevant (Linearity versus Nonlinearity).
Wolf emphasized the following points concerning Bromate: 1) Bromate results from the oxidation of bromide; 2) It occurs most prevalently with ozonation; 3) Exposure data for humans exists including data from intentional and accidental poisonings; 4) It can be fatal in humans; and 5) It causes loss of hearing, kidney toxicity. The focus of current research is to determine if the production of oxidant damage in the nucleus is the key event that is driving the cancer response and if this key event is common to all three tumor sites in the rat.
There is little toxicology data available for chlorate (some toxicology data reveal that it causes oxidant damage to the red blood cells), and there is no cancer data available. Bioassays have started, so the in-life portion will be completed in 2 years, and final data will be available in 4 years. Additionally, there is some evidence that chlorate causes thyroid damage, but it is unknown whether it is a primary effect or secondary to hormone effects (altered iodine uptake).
Wolf reviewed data and information on the toxicity of Haloacetic Acids:
Future work on Haloacetic Acid data include:
The following points were made during the discussion that followed Wolf's presentation:
Research Evaluating the Toxicity of Bromodichloromethane
Rex Pegram, EPA, presented an overview of the methodology and findings from past research on brominated trihalomethanes [Attachment IIIG]. Pegram made the following points: 1) bromine is a better leaving group than chlorine, so compounds containing bromine are generally more reactive; 2) bromine-substituted compounds are more lipophilic, so they can enter more readily into target tissues; and 3) brominated THMs are among the most prevalent DBPs in drinking water, especially when there are higher bromide levels in the source water. Bromodichloromethane is the most potent rodent carcinogen among the THMs and it causes cancer at multiple sites. Cancers of the lower GI tract were induced by two of the brominated THMs in rats and were also correlated with greater exposure to THMs in epidemiological studies. The THMs are volatile, so inhalation is an important exposure route that has not been studied very much thus far. The parent compounds are not believed to be toxic unless metabolized to reactive metabolites that interact with proteins, lipids and DNA to cause toxicity. The brominated THMs are more reactive than chloroform, and are especially more likely to react with DNA and cause mutations.
Human and rodent pharmacokinetic data is expected to be ready for Stage 2. Please see Attachment IIIG for a more detailed discussion of the implications and conclusions of this research, future studies, and a list of references.
Mixture Studies for DBPs
Linda Teuschler, EPA, presented an overview of past, current and future DBP mixtures research [Attachment IIIH]. Mixtures research is important because individuals are exposed to complex mixtures of DBPs, not to single chemicals alone, in the drinking water. Currently, little data on mixtures of DBPs exist, but some preliminary data are available. High dose studies for individual DBPs provide little insight to the health effects of mixtures (even of low dose mixtures). Research on defined mixtures of DBPs have found evidence of increased responses above that expected for single chemicals for liver toxicity in mice and rats exposed to mixtures of THMs, and for liver cancer in mice exposed to dichloroacetic acid and trichloroacetic acid mixtures.
The ILSI Expert Panel Recommendations for Toxicological Testing (March 1998 Report) recommended that DBP risk cannot be assessed by single chemical testing approaches alone. The report suggested the use of modern approaches (e.g., studies relating chemical structure to toxicity, molecular biology and toxicology, knowledge of mechanism of action), the use of a 3-tiered testing approach (i.e., in vitro tests; short term screening tests such as medaka fish or 90 day animal studies; long term chronic bioassays), and a focus on three scenarios: 1) defined (simple) mixtures of less than 10 DBPs; 2) whole mixtures produced by simulating disinfection scenarios; and 3) real drinking water samples or their extracts.
The risk assessment questions that mixtures research should address include:
Teuschler made the following additional points:
Teuschler made the following points in response to questions from participants:
Summary of WHO Environmental Health Criteria Monograph for Disinfectants and DBPs
Hend Galal-Gorchev, World Health Organization (WHO) retired, presented a summary of findings from WHO Environmental Health Criteria Monograph for Disinfectants and Disinfectant By-Products, Summary and Conclusions of International Programme on Chemical Safety (IPCS) Task Group, 17-21 August 1998 [Attachment III.I]. The monograph was authored by four experts and various Disinfectants and DBPs (chlorine, MX, bromate, chlorite, etc.) were evaluated. WHO health-based Guidelines are non-enforceable recommendations that are similar to EPA's MCLG.
Galal-Gorchev made the following points concerning the Characterization of Hazard and Dose-Response: 1) for some chemicals, there were no adequate data to do risk assessment; and 2) for some chemicals, the task group did not have enough information to determine if they were threshold or non-threshold chemicals.
Epidemiological evidence is insufficient to support a causal relationship between bladder cancer or colon cancer and long-term exposure to chlorinated drinking water or DBPs. The results of currently published studies do not provide convincing evidence that chlorinated water or THMs cause adverse pregnancy outcomes.
DBP health effects conclusions were reached independent of concern about balancing risks from microbial contaminants. The main risk-balance recommendation is that disinfection should not be compromised to control for DBPs because the risk from waterborne diseases, such as cholera and typhoid fever is greater than the potential for risk from DBPs.
Panel Discussion on Characterization of Cancer Risks
Bob Morris, Tufts University; Kenneth Cantor, NCI; Bob Tardiff, Sapphire Group; Betty Meek, Health Canada; Jeanette Wiltse, EPA; Phillipe Daniel, Camp Dresser & McKee, Inc.
Phillippe Daniel framed the discussion of the panel by presenting an overview of the major points of concern in DBP risk management [Attachment III.J]:
The following is a summary of points made by panelists regarding the panel discussion questions, and other comments that arose in the course of open discussion:
Question 1: Based on the current database, what are your observations regarding the cancer effects from exposure to DBPs? |
Question 2: What are the consistencies and inconsistencies in the epidemiological and toxicological data? |
Question 3: What are the largest remaining data gaps and uncertainties that need to be addressed to better characterize the cancer effects from exposure to DBPs? |
Additional observations and discussion points
DBP Health Effects: Reproductive and Developmental Risks
Reproductive and Developmental Effects of Exposure to DBPs: An Overview of Epidemiological Data
John Reif, Colorado State University, presented a summary of the epidemiological methods used and outcomes of studies conducted to date, with a focus on TTHMs and discussed the limitations of existing studies of DBPs, including exposure assessment [Attachment IV.A.].
Key points surrounding Adverse Reproductive Outcomes: 1) women experience adverse reproductive outcomes at low doses; 2) there is an accurate recall of exposure since the latency period for developmental effects is short (9-12 months) compared to the latency period for cancer (up to 20 years), which permits an estimation of exposure according to critical periods in fetal development; 3) there have been no human reproductive studies of males endpoints published to date; 4) male infertility has not been studied in relation to exposure to DBPs.
Spontaneous abortion can result from abnormal development or congenital abnormalities, or there maybe problems with the process of pregnancy and uterine growth. Many spontaneous abortions also occur in first month, and they are unrecognized as such since many women may not know that they are pregnant. This accounts for at least 5% or more of spontaneous abortions.
Bias occurs when risk is underestimated if both the normal and diseased group are equally misclassified. Additionally, a confounder must be a risk factor and be associated with the outcome of interest in order to bias the results.
There have been 10 studies published on DBP reproductive effects; 4 are relevant only to water treatment; 6 addressed THM levels. These six studies were discussed in further detail by Reif, see Attachment VI.A. for a more detailed description of these studies.
Reif made the following points in response to questions from the audience:
DBP Health Effects: Reproductive and Developmental Epidemiology: Current and Future Research
Rebecca Calderon, EPA, presented an overview of expert panels discussions from 1993 and 1997, and the schedule for current and planned DBP Health Effects research [Attachment IV.B]. EPA released two reports on reproductive and developmental epidemiology, one in 1993 and the other in 1997. In 1996, John Reif released an Environmental Health Perspective review of the studies - the take home message was that exposure and health end points need to be more carefully assessed. The studies need to be refined with existing data.
Calderon made the following points during her presentation:
In response to questions from the audience Calderon made the following points:
California Studies: THMs in drinking water and Spontaneous Abortion
Kirsten Waller, Sequoia Foundation, reviewed study design and study results for exposure assessment for TTHMS in drinking water and spontaneous abortion and presented an overview of other California current and planned research and schedule for completion [Attachment IV.C.].
The Trihalomethanes in Drinking Water and Spontaneous Abortion study was published in the March issue of the journal Epidemiology. The three communities in California used in this study were chosen because of their water source.
Exposure assessment for the study was performed by identifying drinking water utilities by using the address of the study participants. Quarterly reports from the utilities were obtained to receive THM information. Individual utility data was used, and data were obtained from 78 of the 85 utilities identified in the study. There was no interpolating or extrapolating for unknown data - data that was available for the first trimester was averaged. If THM measurements, for the first trimester, were not available (60% of the cohort had this data) then a 90 day window was used. For 9 percent of the women, an annual THM average had to be used as the level of exposure. An average of how much water the women drank on a daily basis, and bottled water usage was obtained during telephone interviews.
The odds ratio for SAB (spontaneous abortion) of women that drank less than five glasses of water per day with total THM levels greater or equal to 75 µg/L was 1.2. This number is non-significant. The odds ratio of women that drank greater than five glasses of water per day with total THM levels greater or equal to 75 ug/L is 2.0, which is significant. The odds ratios were adjusted for all confounding factors (95% confidence interval).
The strongest association for SAB were seen in women that drank more than 5 glasses of water per day with bromodichloromethane levels greater than 18 ppb. The Odds Ratio was 3, but the number of cases was small, so this outcome is unstable.
A number of studies are currently in progress in California including: (1) reanalysis using a Geographical Information System (GIS) for exposure assessment keyed to specific sampling sites, (2) reanalysis of risks for individual THMs using more complete data, (3) THM modeling in two distribution systems, (4) THMs and menstrual function/sperm parameters, and (4) THMs and adverse pregnancy outcome in a new cohort with high TTHM but low BDCM.
In response to questions from the audience Calderon made the following points:
CDC/EPA Birth Defect Studies
Michele Lynberg, CDC-NCEH, presented a summary of the CDC studies (currently underway or planned) examining the relationships between exposure to DBP and birth defects [Attachment IV.D]. Evaluating the causes of birth defects is difficult and requires a large study population and periconceptional exposure information. Currently, several related birth defects studies are being conducted by CDC and its collaborators (EPA, UNC, CSU) using available birth defect information from: 1) the Metropolitan Atlanta Congenital Defects Program (MACDP), an established surveillance system in existence since 1968; 2) the Atlanta Birth Defects Risk Factor Surveillance Project (BDRFS), a case-control study based on the MACDP, conducted during 1993 - 1996; and 3) the National Birth Defects Prevention Study (NBDPS) which began in 1997 and is based on the surveillance systems in metropolitan Atlanta and 7 other geographic areas (Alabama, Arkansas, California, Massachusetts, New Jersey, New York, and Texas). These birth defects databases are being linked to historical water utility data and reported water use characteristics.
Information was collected from seven water utilities (ten treatment plants) in metropolitan Atlanta. To coincide with the BDRFS case-control study, all existing THM (monthly and quarterly) and chlorine residual (almost daily) data were abstracted for the years 1992-1996. Data collection is complete and analysis is under way. Three exposure matrices are being used: measured THM, predicted THM (based on correlations with chlorine residual), and calculated chlorine demand values. Spatial and temporal boundaries were assigned around sampling locations and subjects date of conception, respectively. Simultaneously, correlation equations between THM and calculated chlorine demand have been developed so that THM values can be predicted in areas where no THM monitoring data are available.
A multi-site study, based on the National Birth Defects Prevention Study, is being undertaken through an interagency agreement between CDC and EPA. The time line for the currently funded birth defects research, which continues through 2001, was discussed.
In addition, there is potential for expansion of the multi-site study to other participating Centers for Birth Defects Research and Prevention. The investigators also plan to conduct an exposure assessment study in Cobb County, Georgia (where the highest level of chlorinated THM in Atlanta occur) and in a selected county in Texas where the prevalence of brominated compounds is high.
Lynberg made the following points in response to questions from participants:
New Jersey Studies
Judith Klotz, NJDPH, presented an overview, and the results of the New Jersey studies done for reproductive outcomes and drinking water contaminants [Attachment IV.E]. The first study included a wide variety of reproductive outcomes, while the second concerned only neural tube defects. The original study was published in the American Journal of Epidemiology in 1995. Neural tube defects were the most significant outcome related to increased THM (dose-response effect).
In the follow-up study there were 112 cases and 248 controls. However, addresses at time of conception could not be determined for 25 percent of subjects, but addresses at birth were known. Data on water source were obtained from the NJ Department of Environmental Protection and the local water companies, and water monitoring data were retrieved from the NJ DEP. Timing in the study was very important, because of the time of susceptibility for neural tube defects. Tap sampling for THMs, Haloacetics, etc. was done 1 year after the study period.
Haloacetics had insufficient data to draw conclusions. Haloacetonitiles showed no clear relationships.
The studies had different designs, and covered a different geographic area. However, they had showed similar associations for NTDs and THMs.
Toxicological Aspects of DBPs - Introduction
Fred Hauchman, EPA, presented a brief history of research on DBP toxicological data. Funding in these areas have been major thrusts for EPA's research program. The sciences of environmental epidemiology and toxicology should go together systematically in the future to look at biomarkers and mechanism of action.
Reproductive Toxicology: Overview of Current Science and Current and Future Research and Schedules for Completion
Gary Klinefelter, EPA, presented overviews of what we know about reproductive toxicology of DBPs and what is planned for the future, current testing strategies and pertinent results, and the importance of predictive mechanisms and biomarkers [Attachment IV.G]. In 1993 a panel of ILSI and EPA experts was formed to review epidemiology and animal data. The panel recommended that data gaps are filled by using screening strategies especially with fertility data, mode of action, and biomarkers. Data gaps still exist, but progress is being made.
Klinefelter covered the history of reproductive toxicology, the work of the Research Triangle Park (RTP) Drinking Water DBP research team, DBP testing strategy, NTP's 35 day reproductive and developmental screen, the test in males and results of other DBP toxicological research - see Attachment IV.G for more detail.
Klinefelter also made the following point in discussing the slides:
3Ability to move and the structure of the sperm. |
Haloacetic Acids effect male reproduction (fertility). Some effect at low doses, may be mediated through specific proteins. When we look at gestation through puberty these effects will be maintained. Brominated acids are more potent than the chlorinated species.
Developmental Toxicology: Overview of Current Science and Current and Future Research and Schedules for Completion
Sid Hunter, EPA, presented an overview of developmental toxicology literature and an overview of the current research program being conducted through the National Toxicology Program and EPA, National Health and Environmental Effects Research Laboratory including bromodichloromethane. Hunter also included an overview of Screening Studies (What questions can we ask?) and Mechanistic Studies (What are the questions?) [Attachment IV.H].
Hunter made the following points during his presentation:
In response to questions from participants, Hunter made the following points:
Panel Discussion on Characterization of Reproductive and Developmental Risk
John Reif (Colorado State University); Gary Kimmel, (EPA); Phillipe Daniel (Camp Dresser & McKee, Inc.); Fred Hauchman (EPA); Kirstin Waller (Sequoia Foundation); Judith Klotz (NJDPH); Gary Klinefelter (EPA)
Panelists were asked to answer the questions below in opening statements. Panelists then followed with an open discussion, including questions from the audience, of the DBP reproductive and developmental risks. The following is a summary of points made by panelists regarding the panel discussion questions, and other comments that arose in the course of open discussion:
Question 1: Based on the current database, what observations can be drawn on the reproductive and developmental effects from exposure to DBPs? Is there biological plausibility that exposure to DBPs can attribute to the types of adverse reproductive and developmental effects seen in the laboratory and human studies?
Question 2: What are the largest remaining data gaps and uncertainties that need to be filled to better characterize the reproductive and developmental health effects from exposure to DBPs?
Other observations and discussion points (but no agreement)
Summary of Reproductive and Developmental DBP Health Effects Panel Discussion
Phillippe Daniel, Camp Dresser & McKee, Inc., presented the following points in a summary of the key points from the Panel's discussion:
Microbial: Background for Long Term 2 Enhanced Surface Water Treatment Rule
Pathogen Occurrence in Tap Water
Mark LeChevallier, American Water Works Service Company, gave an overview of what is known about occurrence of protozoa and viruses in drinking water and reviewed the current understanding of pathogen occurrence as it relates to distribution system maintenance strategies [Attachment V.A.1].
Data on protozoa in tap water are mixed with respect to protection for Cryptosporidium [Attachment V.A.2]. Monitoring data shows low levels of pathogens in tap water. Most systems rely on chlorine for disinfecting, but it is not effective against Cryptosporidium. Past outbreaks have been related to treatment barrier breakdown, except for Las Vegas. When barriers were replaced in these systems the disease was no longer evident. A broad survey was done in 1995 to determine protozoa existence in drinking water: 55 percent of plants were positive for Crypto oocysts. The meaning of this high rate of occurrence of oocysts in systems that had no apparent water associated cryptosporidiosis disease is unclear. The analytical method used in this summary (immunofluorescenct staining) does not indicate viability or infectivity so does not answer public health significance.
Epidemiological studies are difficult to interpret and associate to a particular pathogen or etiological event. Best evidence of pathogen occurrence would be a C. parvum(4) cell culture viability/infectivity assay which can be applied to drinking water monitoring which is (viable) in drinking water.
4C. parvum is a strain of Cryptosporidium which is known to cause disease. |
LeChevallier described a project being conducted by the AWWSC to measure live, infectious C. parvum in the filter effluents of 80 surface water treatment plants. The two-year study will begin in the Spring of 1999 and be completed in 2002. Turbidity and particle count data will be collected to correlate breakthrough of live oocysts with treatment optimization.
Since 1995 about 4.5% of waterborne disease outbreaks were due to viruses. There are no methods available to culture all viruses (e.g. Norwalk) that are hazardous to public health. The data do not indicate that viruses survive when other pathogens are removed and inactivated. Phage was found in most surface water supplies. ICR data showed that 13% of raw water samples taken were positive for viruses (1 - 28 Most Probable Number/100 L). All of the finished water samples (30) were negative.
Additional treatment barriers to protect drinking water are:
LeChevallier reviewed a list of newly emerging organisms [Attachment V.A.3]. Mycobacterium avium is high priority because it is chlorine resistant (it is acid fast, waxy, and not water permeable) and it can regrow in biofilms after treatment. It normally infects immunocompromised persons (e.g. AIDS patients) when it is ingested. The relative contribution disease of M. avium from drinking water is unknown.
Preventing contamination should be a priority. Pressure fluctuations in the distribution system can cause contaminated water to leak into the system. Many factors influence water pressure and can cause fluctuations. Water leakage out of the distribution system of 10 and 40 percent is not uncommon; water leakage in to the distribution system can not occur if positive pressures are maintained, but this is not always the case. Hydraulic modeling can be used to understand pressure surges. High speed pressure gauges can detect these pressure transients.
LeChevallier also discussed the effect of monochloramine disinfection on the risk of nosocomial Legionnair's disease (see Attachment V.A.4).
The following points were discussed by LeChevallier in response to questions from participants:
Overview of Types of Health Effects Data (Microbes) and How Data is Used in Decision Making
Stig Regli, EPA, reviewed the major regulatory questions for Stage 2 microbial rule and discussed information used to assess risks from pathogens and how this influences regulatory criteria. Regli also covered the relevance of waterborne disease outbreak information to development of the regulations, reviewed how various types of epidemiology studies can contribute to regulatory decision making, and presented an overview on how dose response data influences regulatory focus, and how is it used in regulatory impact analysis [Attachment V.B].
In 1994 stakeholders involved in the regulatory negotiation agreed to:
In 1997 EPA convened another FACA to develop recommendations on how to best move forward with the IESWTR in the absence of ICR data. As a result of these deliberations, EPA issued a NODA in November 1997 and promulgated the IESWTR in December 1998. EPA is also developing a LT1ESWTR that will pertain to systems serving less than 10,000 people. The major focus of the IESWTR and LT1ESWTR is to improve performance and reliability of physical removal of pathogens through tighter turbidity standards.
Major regulatory questions for LT2ESWTR include:
Regli made the following points in response to questions from participants:
Epidemiology: Overview of Current Science Including Sensitive Subpopulations
Dennis Juranek & Deborah Levy, CDC, discussed the use of epidemiology in understanding microbial risk [Attachment V.C]. Levy began by presenting an overview of the nation's waterborne disease outbreak surveillance system. For passive surveillance, unit of analysis is outbreak not single cases and there are many factors that affect whether waterborne disease outbreaks are recognized and investigated by state or federal health agencies.
In many outbreaks, it is common for the etiological agent to be unidentified. Fifty (50) percent of outbreaks come from a well water source; 31.8 percent of outbreaks come from surface water. Actual likelihood of outbreaks being detected and reported is effected by the size of the outbreak, severity, public awareness that an outbreak is occurring, investigator interest, and resources of local health department. Surveillance system sensitivity is probably low. Many factors contribute to not reporting, such as: a person not going to a physician when ill, lack of physician awareness, lack of lab testing and confirmation, lack of reporting by the physician, lack of timely review by local health dept, etc. Hence, there is probably more waterborne disease occurring than is reported.
The Foodborne disease active surveillance network (Foodnet) included questions about water. It was done through random phone calling of the general population, physicians, and labs. The survey revealed that 11 percent of the population had diarrheal episodes (1.4 episodes/year); of these 8 percent visited a health care provider and 2 percent provided a stool specimen. The probability of the general population being tested for Cryptosporidium is related to the specialty of the practitioner. An infectious disease practitioner is more likely to test for Cryptosporidium. Doctors generally assumed that the lab would automatically test for Cryptosporidium. Only 5 percent of labs routinely test for Cryptosporidium or cydospora; 50 percent routinely test for E. coli oocysts; none routinely test for viruses.
Payment waterborne disease studies estimated that 14 percent of diarrhea was attributable to waterborne illness. The results suggested that the distribution system was a potentially significant source. Extrapolation of this data to the US population suggests that there may be as many as 50 million cases of diarrhea per year.
The risk of Cryptosporidium the drinking water is unknown; it depends on the quality of source water and the efficacy of treatment facility. The risk of infection depends upon immunity and behavior. The risk of developing severe disease depends on immune status. The populations at risk of severe disease from Cryptosporidium are: AIDS patients, persons with congenital defects in the immune system, and those taking immunosuppressive medications. Age alone is not an indication of increased risk. In Milwaukee, the elderly were less likely to be infected, but they were more likely to be hospitalized. Secondary spread of Cryptosporidium is most common from 0 - 2 year old children.
Juranek made the following points in response to questions asked by meeting participants:
Microbial Pathogens and Epidemiology: Current and Future Research and Schedules for Completion, EPA/CDC/AWWARF Household Intervention Study
Rebecca Calderon, EPA, presented an overview of current and future microbial pathogen and epidemiology studies [Attachment V.D]. The goal of these studies is to look at surveillance to determine what human disease is occurring in the population, and the relationship with pathogen occurrence. Two questions need to be answered about endemic illness regardless of etiology and individual pathogens.
Calderon discussed the following studies:
There were 22 identified waterborne outbreaks in 1995-1996 in the US. In 34 percent of the cases, the etiological agent was not identified. International projects do not depend as much on monitoring and reporting as in the US. Studies are planned or ongoing in Great Britain, Italy, New Zealand and France.
Epidemiology: The Use of Serology to Study Prevalence of Cryptosporidiosis Due to Drinking Water
Jeff Griffiths, Tufts University, presented an overview of serology studies to estimate occurrence of cryptosporidiosis due to drinking water, and the Pediatric Serologic epidemiology study comparing populations served by unfiltered water from protected watershed and filtered water from unprotected watershed [Attachment V.E].
There is no one method that is superior or complete for assessing Cryptosporidium exposure. All tests seem to underestimate exposure and, hence, are conservative. Serological methods are important because they permit comparisons among studies. Cryptosporidium is a complex parasite B immunity is short-lived. Once infection occurs, T cells and gamma interferon are crucial to recovery. Antibodies are helpful, but are not crucial to recovery. The Western blot and ELISA serological testing methods are used to detect infection. The Western blot may be the superior testing method, but it is costly and technically complex. No one method gives you the complete picture.
In the Providence Rhode Island data the serological testing revealed a correlation between oocyst antibodies and age. Over 50 percent of children aged 1-2 had oocyst antibodies and/or tissue changes. In Massachusetts, serological testing in children was able to occur because the department of public health had obtained blood samples. The zip codes of the children were known, so that the water source and supplier could be identified. The tests revealed that those in protected water supplies were less likely to have anti-oocyst antibodies (IgM, IgA, & IgG). It was predicted that only 1 in 10,000 infections are reported (range is 3,000 - 40,000). The results of this study supports the idea that we should have a protected water supply that is free of animal runoff or human sewage.
Other important unanswered questions/issues for Cryptosporidium exposure include:
Jeff Oxenford, AWWARF, presented the results of a two-city study that compared the rates for Cryptosporidium infection between populations being served surface water vs. ground water. Approximately 500 sera samples were collected from blood banks in each city and were analyzed by the Western Blot technique. Detail surveys were also obtained to identify other possible exposures. The project included extensive QA/QC procedures and received extensive review.
Studies results did show a significant different between the serological response in two cities with the surface water city having a higher response than the ground water city. Weak correlations were found with age, travel, gender, working or school located in another city, and using an alternative water source. No correlations were found between serological response and episodes of diarrhea, handling livestock, drinking untreated water or swimming.
What are the implications of the study? While a difference was observed between the two-cities studied, caution must be maintained in interpreting the results. Questions that remain include: 1) What is the endemic level of Cryptosporidium infection in the U.S.? Were infection rated in these two cities within ranges typically found? 2) Will this relationship hold for other cities? 3) Were there other sources of Cryptosporidium that could account for the differences? 4) What is the relevance of serological response to disease?
In response to questions from participants Griffiths and Oxenford discussed the following points:
Time Series Studies on GI Illnesses Related to Turbidity
Bob Morris, Tufts University, presented time series studies and their use [Attachment V.F]. Waterborne disease outbreaks are, by nature, time series events. An outbreak is characterized by a period of contamination of the water supply followed at some time lag by an increase in disease in the community served by that water supply. In order to understand how time series studies fit in with other methods for studying waterborne disease it is useful to look at the mechanisms by which pathogens spread in the community and how available methods assess the role of water in that spread.
The pathways by which fecal-oral pathogens (i.e., GI pathogens spread by ingestion of fecal material) spread are depicted in Figure 1, Attachment V.F.. Waterborne pathogens reach host populations from the distribution system. Once hosts are exposed, they may become infected and develop symptomatic disease, and may, in turn, spread the disease through direct contact, or through contamination of surfaces, food, or swimming pools. Thus, cases of infection and disease caused directly by exposure to contaminated water will tend to be amplified through secondary spread of the pathogen. This has important implications for studies that focus only on disease caused directly by the spread of pathogens in drinking water since they will not include the effects of amplification outside of the home.
Figure 1 also depicts the host transitions that occur in a person following exposure to a pathogen. The exposed individual may or may not develop an infection and, if infected, may or may not develop symptomatic disease. The relationship between exposure and disease depends upon the characteristics of the host (e.g., immune status, nutritional status, age). A person with symptomatic disease may or may not seek medical care and, in turn, may or may not be tested, diagnosed or reported. Consequently, studies of waterborne disease that rely on passive surveillance data will only characterize a small portion of the symptomatic disease.
Recently introduced time series methods consider the incidence of disease in the entire community as a function of changes in drinking water quality over time. These studies can utilize any sort of data describing exposure and a relevant health outcome as time series. The ability to use routinely collected data such as HMO or emergency department billing data to describe the occurrence of gastroenteritis allows these studies to be conducted relatively inexpensively without requiring the use of passive surveillance data which has the limitations described above.
The time series method was first used in 2 studies (Morris et al.) of the 1993 waterborne outbreak in Milwaukee which looked at emergency room visits, gastrointestinal events, and water treatment plant's turbidity levels before the outbreak to determine if gastrointestinal events and turbidity levels were correlated. A non linear model - temporal exposure response model (TER) was used for data analysis. A time lag between increased turbidity levels and the onset of a gastrointestinal event was factored in (a time lag between increased turbidity and onset of gastrointestinal event was noted at 6-7 days with a second peak occurring about 1 week later).
Results show that there may have been a low level contamination prior to the 1993 outbreak - this was particularly evident for children. A subsequent study conducted in Philadelphia by Schwartz et al had similar results.
The advantages and disadvantages of time series studies mentioned by Morris are summarized below:
Advantages:
Disadvantages:
This tool can be used retrospectively and prospectively. You can look at historical data to establish a signature for a given pathogen, and once you understand the relationship, you may be able to predict the impact of a change in water quality. Improvements in exposure assessment and measurement of health outcomes can improve the sensitivity of this technique. A recently funded CDC study will use serological data as the health outcome with the data analyzed as time series to give a pathogen specific time series study.
Dose-Response: Overview of Current Science
Charles Haas, Drexel University, presented an overview of how dose response studies are conducted, their limitations in study design and what general conclusions that can be drawn. Haas also discussed what is involved with extrapolating dose response data from healthy populations to sensitive subpopulations, and from high dose to low dose [Attachment V.G].
A "typical" dose-response study does not consider minimal infectious dose, but median infectious dose. Multiple endpoints, multiple outcomes, number of infections, and number of subjects that develop illness, are measured for each dose group. Models should be biologically plausible. Threshold approaches to model dose response should not be used. No human data substantiate models that allow thresholds and there is no biological plausibility for these models.
Morbidity data is more scarce than infectivity data. The fraction of people that are ill once infected is simple to calculate, since there is no dose dependency. This is true for most pathogens except for Vibrio cholera - which has dose dependent relationship with morbidity.
Remaining questions include:
Cryptosporidium parvum Volunteer Study
Cynthia Chappell, University of Texas-Houston, presented an overview of the Cryptosporidium parvum (dose-response) Volunteer Study. The objective of the study was to:
Volunteers in the study had to be negative for specific anti-Cryptosporidium antibodies by ELISA, healthy (not IgA deficient and they had to have a certain number of T cells), and they could not have elderly persons or children under 2 years of age living in the household. Additionally, they had to pass a written examination about the organism and the study. The study population was mostly Caucasian, but had representation in Hispanic, black and Asian ethnicities; consisted of males and females, and the age range was 18 - 50 years (mostly 25 - 35). To date there are about 110 study volunteers.
The challenge dose was prepared from calves - genotype 2 isolates. The route of administration was via gelatin capsule. Stool was collected for a total of 6 weeks: on a daily basis for the first 14 days and three times a week for the next 4 weeks. A physical exam was done daily for 2 weeks and twice weekly for the next 4 weeks. Each volunteer kept a personal health diary to record any and all symptoms experienced during the study, including gastro-intestinal symptoms.
The duration of the infection was 1 - 11 days (median 6 days). Mean fluid loss was 1180 grams with a maximum fluid loss of 2846 grams over 5 days. All cases were self-limited and cleared the fecal oocysts (detected by direct fluorescence). 88 percent of the volunteers cleared their infections within 14 days; one excreted organisms for 38 days. The incubation period was approximately 5-7 days and did not vary significantly among isolates.
Susceptibility to re-infection was tested: 19 individuals were re-challenged with a single dose of 500 oocysts. Total oocyst shedding from re-infection was decreased dramatically. The prepatent period or duration of oocyst shedding were not significantly different from primary challenge, and the illness attack rate remained the same (58%) when compared to the original infection. However, there were fewer unformed stools after re-challenge compared to the original infection.
Serologically positive volunteers were selected on the basis of IgG reactivity. These individuals developed infection and illness, but required much higher oocyst doses to do so. ID50 in these individuals was approximately 20-fold higher than in seronegative subjects. Also, the number of oocysts shed and the number of infected individuals shedding oocysts were significantly decreased, indicating a much reduced potential for secondary transmission. Antibody positive volunteers had longer diarrhea duration compared to antibody negative volunteers, indicating that seropositive people exposed to high levels of oocysts may have a more severe illness than those who were antibody negative. The reason for this observation is unclear, but may indicate an enhanced mucosal response to the infection. In these individuals, diarrhea may be considered part of the protective response- that is, an enhanced shedding of infected cells and removal of parasites via the stool. However, no increase in total stool weight was noted.
These studies have provided many tissue and oocyst samples for continued studies. Next research steps will be the examination of genotype 1 isolates, as well as non-parvum species studies (important for immunosuppressed patients).
In response to questions from participants Chappell made the following points:
Studies on the Infectivity of Norwalk and Norwalk-Like Viruses
Christine Moe, University of North Carolina, discussed the infectivity of Norwalk and Norwalk-like viruses [Attachment V.I]. Norwalk virus (NV) and related small round structured viruses (SRSVs) are the leading cause of epidemic viral gastroenteritis and are important waterborne and foodborne pathogens. Risk assessment for these viruses in water and food requires data on dose-response.
A double-blinded human challenge study was conducted to determine the dose-infectivity relationship for NV in healthy human volunteers with various levels of pre-existing anti-NV IgG. The study was conducted in 3 rounds. Each round had 15 subjects randomized to one of 3 doses of safety-tested NV inoculum which was tittered by electron microscopy and endpoint titration RT-PCR. Subjects were monitored for gastrointestinal (GI) symptoms for 5 days post-dosing and returned for Day 8, 14 and 21 follow-up visits. Viral excretion was determined by RT-PCR, and seroconversion was measured by enzyme immunoassay. Six doses, ranging from approximately ten (10) PCR detectable units (PDU) to 1 x 107 PDU, were examined with 5 or 10 subjects per dose. Overall, 20 subjects became infected: 19 excreted virus and seroconverted and 1, at the lowest dose, seroconverted but had no GI symptoms or detectable NV RNA in stools.
The predominant symptoms were nausea and vomiting, and the duration of illness was less than 48 hours. Although the illness associated with infection was mild, about 50% of infected subjects reported that they could not have gone to work during their illness. Viral shedding was typically for 6-8 days post-dosing (maximum 20 days). The highest infection rate (70%) was observed among ten people who received a mid-range dose, suggesting that response to NV ingestion may be related to host factors as well as dose. Pre-existing IgG antibodies to NV did not protect against infection. The data did not show a simple dose-response relationship. The best fit to the data was with a two-population beta-Poisson model that modeled the dose-infectivity relationship for subjects with pre-existing IgG separately from those without pre-existing IgG. Subjects with pre-existing IgG were infected at lower doses and infection was related to dose. The results of this study will be valuable for estimating the risk of NV and related SRSV infection associated with exposure to contaminated water and food and to establish exposure limits for SRSVs to reduce waterborne and foodborne disease. Further studies of low NV doses with a larger sample size are needed.
Panel Discussion on Characterization of Microbial Risk
Mark LeChevallier, AWWSCO; Dennis Juraneck, CDC; Charles Haas, Drexel Univ.; Jeff Griffiths, Tufts Univ.; Stig Regli, EPA; Stephen Edberg, Yale Univ.
Panelists were asked to answer the questions below in opening statements. Panelists then followed with an open discussion of the risks related to microbial contamination in drinking water, including questions from the audience.
Question 1: What is the public health risk associated with microbial contamination?
Question 2: Source water related? Distribution system related?
Question 3: What are the key pieces of information needed to estimate risks?
Question 4: To what extent may there be risks to sensitive Subpopulations?
Question 5: To what extent is research available to address this question? (What further research is needed?)
Question 6: To what extent do you believe it is appropriate to use Cryptosporidium as a target organism for controlling pathogens in general?
Other Observations
Closing Remarks
Cynthia Dougherty, EPA, thanked all of the participants for taking part in the workshop. Dougherty reminded participants that their present efforts need to be focused on short term needs to support decision making, and policy conclusions from this workshop. Beginning with the March 30, 1999 M/DBP Stage 2 Federal Advisory Committee organization meeting, participants will begin to discuss policy conclusions the EPA should draw from the data presented. Dougherty thanked all participants for their contribution to the success of the Workshop and their continued efforts and adjourned the meeting.
|