EPA-820-R-14-009 Microbiological Risk Assessment (MRA) Tools, Methods, and Approaches for Water Media December 2014 Office of Science and Technology Office of Water U.S. Environmental Protection Agency Washington, DC 20460 Microbial Risk Assessment Tools U.S. EPA Office of Water Notice The tools and procedures set forth in this document are intended to describe the United States (U.S.) Environmental Agency’s (EPA) approach for conducting or revising microbial risk assessments to protect human health from exposure to water-based media. They are also intended to serve as guidance to EPA and EPA contractors for conducting microbial risk assessments. This document has been reviewed in accordance with Agency policy and is approved for publication and distribution. Mention of commercial products, trade names, or services in this document or in the references and/or footnotes cited in this document does not convey, and should not be interpreted as conveying, official EPA approval, endorsement, or recommendation. ii Microbial Risk Assessment Tools U.S. EPA Office of Water Foreword This document presents a series of tools, methods, and approaches for planning and conducting microbial risk assessments in support of human health protection for water-based media. This document provides guidance for microbial risk assessments conducted or revised by EPA or EPA contractors and should not be considered regulatory. The tools and approaches described herein focus on conducting risk assessment for water-related media (such as microorganisms in treated drinking water, source water for drinking water, recreational waters, shellfish waters, and biosolids), but are sufficiently general to help guide the development of microbial risk assessments of pathogens that might be found in food, food products, or other media. iii Microbial Risk Assessment Tools U.S. EPA Office of Water Acknowledgments Project Leader Stephen Schaub* U.S. EPA Office of Science and Technology U.S. EPA Technical Reviewers Alfred Dufour U.S. EPA Office of Research and Development/National Exposure Research Laboratory Stig Regli U.S. EPA Office of Ground Water and Drinking Water Philip Berger U.S. EPA Office of Ground Water and Drinking Water Sharon Nappier U.S. EPA Office of Science and Technology John Ravenscroft** U.S. EPA Office of Science and Technology * Principal author ** Contact Initial draft report developed by ICF International under U.S. EPA Contract 68-C-02-009; interim draft developed by Tetra Tech Clancy Environmental, Soller Environmental, and ICF International under U.S. EPA Contract EP-C-07-036; final report developed by ICF International and Soller Environmental under U.S. EPA Contract EP-C-11-005. Contributing authors: Audrey Ichida, Jeffrey Soller, William Mendez, Jonathan Cohen, Timothy Bartrand, Mark Gibson, Jennifer Welham, Margaret McVey, Gunther Craun, Walter Jakubowski, Cynthia McOliver, and Martha Embrey. The International Life Sciences Institute Risk Science Institute (ILSI-RSI) under cooperative agreements with the U.S. EPA Office of Water, Office of Science and Technology, Health and Ecological Criteria Division, developed a report titled Revised Framework for Microbial Risk Assessment to address critical areas of microbial risk assessment (ILSI, 2000). This MRA Tools document evolved out of that report. The steering committee for the development of that report included the following: Stephen Schaub U.S. EPA Office of Science and Technology, lead Gunther F. Craun G.F. Craun & Associates Alfred Dufour U.S. EPA Office of Research and Development Charles Gerba University of Arizona Charles Haas Drexel University Alan Roberson American Water Works Association Mark Sobsey University of North Carolina iv Microbial Risk Assessment Tools U.S. EPA Office of Water External Peer Review Workgroup This document has been subject to external peer review following the Office of Management and Budget’s Peer Review Guidance (2004) and EPA’s Peer Review Handbook. Potential areas for conflict of interest have been investigated via direct inquiry with the potential peer reviewers and review of their current and past affiliations. Reviewers did not have conflicts of interest. Peer reviewers included: Margaret Coleman Syracuse Research Corporation (currently Coleman Scientific Consulting) Joseph Eisenberg University of Michigan Charles Gerba University of Arizona A subsequent draft version of this document was reviewed by EPA’s Science Advisory Board – Drinking Water Committee. The committee met on September 21-22, 2009. This document has been revised in response to their comments. v Microbial Risk Assessment Tools U.S. EPA Office of Water vi Microbial Risk Assessment Tools U.S. EPA Office of Water Table of Contents Notice .............................................................................................................................................. ii Foreword ........................................................................................................................................ iii Acknowledgments.......................................................................................................................... iv External Peer Review Workgroup ...................................................................................................v Tables, Figures, and Text Boxes .................................................................................................... ix Abbreviations and Acronyms ........................................................................................................ xi Executive Summary ..................................................................................................................... xiii 1. Introduction ................................................................................................................................1 1.1. Purpose and Scope of this MRA Tools Document............................................................... 1 1.2. Development of the MRA Tools Document ........................................................................ 3 1.3. MRA Framework ................................................................................................................. 7 1.4. General MRA Concepts ..................................................................................................... 11 1.5. Microbial Risk Assessment for Decision-Making ............................................................. 12 1.6. Factors Unique to Microbial Risk Assessment as Compared to Chemical Risk Assessment ................................................................................................................. 13 1.6.1. Microbial Growth and Death .................................................................................... 13 1.6.2. Detection Methodologies .......................................................................................... 14 1.6.3. Genetic Diversity of Pathogens ................................................................................ 15 1.6.4. Host Immunity and Susceptibility ............................................................................ 15 1.6.5. Dose-Response Range can be Broad ........................................................................ 15 1.6.6. Secondary Transmission ........................................................................................... 15 1.6.7. Heterogeneous Spatial and Temporal Distribution ................................................... 16 1.6.8. Zoonotic Potential ..................................................................................................... 16 2. Planning and Scoping and Problem Formulation ....................................................................17 2.1. Introduction to Planning and Scoping and Problem Formulation ...................................... 17 2.2. Overall Problem Formulation and Planning and Scoping .................................................. 20 2.2.1. Statement of Concern ................................................................................................ 21 2.2.2. Statement of Purpose and Objectives ....................................................................... 21 2.2.3. History and Context within the Agency.................................................................... 23 2.2.4. Scope ......................................................................................................................... 23 2.2.5. Questions to be Addressed in the Risk Assessment.................................................. 25 2.2.6. Conceptual Model and Narrative .............................................................................. 26 2.2.7. Planning and Scoping: Analysis (Operational) Plan ................................................. 28 2.3. Analytical Approaches ....................................................................................................... 28 2.3.1. Representative Model Forms for MRA Risk Estimation .......................................... 30 2.3.2. Data Representation in MRA Risk Estimation Models ............................................ 35 2.4. Elements to Consider During Problem Formulation .......................................................... 40 2.4.1. Infectious Disease Hazard Characterization ............................................................. 40 2.4.2. Initial Host Characterization ..................................................................................... 46 2.5. Linkage between Problem Formulation