TOHTED STATES ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON D.C.
August 18, 1992
OFFICE OF
ME ADMNSTRATOK
SCIENCE ADVISORY BO AKD
EPA-SAB-DWe-LTR-92-011
Honorable William K. Eeilly
Administrator
U.S. Environmental Protection Agency
401 M Street, SW
Washington, DC 20460
Subject: Review of the Drinking Water Criteria Document for
Cryptosporidium
Dear Mr, Reilly:
The Drinking Water Committee (DWC) of the Science Advisory Board (SAB) met on
February 11-12, 1992 and reviewed the Drinking Water Criteria Document for
Cryptosporidium.
Overall, the Drinking Water Committee considers the draft document to be inadequate
as a criteria document. This is because of the following deficiencies; 1) it does not reflect
the current state of knowledge; 2) it is superficial in its coverage of information on
Cryptosporidium in drinking water and the aquatic environment, especially concerning
treatment efficacy; 3) it does not identify the important gaps in scientific knowledge and
understanding of Cryptosporidium or its public health significance in drinking water; 4) it
does not identify the scientific needs that must be met to go forward with a risk assessment;
and 5) it draws no conclusions and makes no recommendations on future scientific directions
to decide if Cryptosporidium in drinking water should be regulated and if so, how to regulate
it.
The Drinking Water Committee recommends a revision of this Draft Criteria
Document on Cryptosporidium in Drinking Water that is responsive to the deficiencies and
errors noted in this review. A comprehensive revision of the document is necessary in order
to move forward with a scientific risk assessment and risk characterization. Tie revision
should include an insightful and critical analysis of the following topics: 1) the organism and
its diseases in humans; 2) the sources and occurrence of the organism in water and the role
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of water in its transmission; 3) the efficacy of water treatment processes for its removal and
inactivation; and 4) the risk of drinking water as a source of human exposure, infection and
illness. The revised document should identify and prioritize the gaps in current scientific
knowledge that must be filled in order to conduct a comprehensive risk assessment according
to a systematic conceptual framework, A desirable conceptual framework includes the
following key points: hazard identification, exposure assessment, effects assessment based on
dose-response and epidemiological data, risk assessment and risk characterization, and
finally, the scientific basis on which to proceed with risk modelling, quantitative risk
analysis, and the known relative risks (compared to disinfectants and disinfection
by-products),
The sections of the document that concern Cryptosporidium in water and elsewhere in
the environment are lacking in both detail and important scientific information that is already
available. A significant document that is more comprehensive and more analytical about
Cryptosporidiutti in drinking water has already been published in Great Britain, but this
document was cited only superficially (Badenoch, J, (1991) Cryptosporidium in Water
Supplies, HMSO, London), The Drinking Water Committee believes that the British
document is a much better source of information than the draft document under review. The
British document contains important conclusions and recommendations that should have been
considered in this draft criteria document.
Thank you for the opportunity to review this draft criteria document and to provide
the above advice. In addition, we have included specific comments as an attachment to this
letter. W& look forward to your response to the advice contained in this letter.
Sincerely,
Dr. Verne Ray, Chair
Science Advisory Board Drinking Water Committee
Attachment
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Specific Comments and Questions
Page 2, second paragraph, line L It is stated that the cryptosporidium organisms are 2-6
micrometers in diameter. However, there is evidence that the range of diameters may be
greater than this.
Page 2, second paragraph, lines 5 and onward. Cryptospoiidium was more than a
"curiosity" and was recognized as an important pathogen in cattle before 1980.
Page 3, 2nd paragraph. Hie information here concerning sources of exposure (human versus
animal) and transmission routes are unclear and maybe misleading. Both humans and some
other animals, such as cattle, are important reservoirs of the organism. Modes of
transmission include person-to-person, animal-to-person, and fecally contaminated vehicles,
including water. The airborne route of exposure, if it occurs in humans, must be
documented, because the fecal-oral route is the only one generally recognized. The relative
importance or significance of these different exposure routes is variable and uncertain,
because it depends on population, location, environment and other demographic factors.
Page 3, paragraph 4. This paragraph is poorly written because it includes too many topics
that should be presented separately and more clearly. The paragraph covers susceptibility,
clinical illness, and resistance in both normal and immunosuppressed or immunodefkient
persons. The paragraph also includes occurrence (prevalence and incidence) data, which are
presented unclearly and incompletely. They should be presented more clearly and
comprehensively in a separate paragraph.
The importance and significance of respiratory infection and illness must be addressed more
clearly in this document. It is not clear that respiratory transmission occurs, and the
significance of respiratory illness (as seen in immunosuppressed individuals) relative to
exposure from drinking water is also unclear.
Page 4, paragraph 3. The outbreak in Texas was not conclusively proven to be
cryptosporidiosis. A virus (Norwalk virus) was also involved. Furthermore, it is uncertain
that colifoim bacteria were adequately controlled at the time of this outbreak. Colifoims
were not detected, but this does not prove that they were being adequately controlled when
the likely exposure to contaminated water was occurring.
A-l
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Page 5, 2nd paragraph, last sentence. It is impEed that many other waterbome outbreaks of
Cryptosporidium hswQ occurred. These are not documented, detailed or discussed. If there
are many such outbreaks, then their characteristics and the circumstances surrounding their
occurrence should be detailed.
Page 5, 3rd (last) paragraph, 1st sentence. Data from one survey (not referenced) are
presented here. There have been other surveys. A more representative summary of all
survey data should be given.
Page 6, 3rd paragraph. The similarities between Cryptosporidium and Giardia are largely
superficial, and so this paragraph should be re-worded to make that dear. The paragraph
should also be re-worded to state more clearly the purpose of the SWTR (it regulates other
microbes besides Giardia). It should make clear that the treatment requirements for Giardia
cannot be applied to or interpreted for Cryptosporidium because of a lack of occurrence and
treatment date on Cryptosporidium. The last sentence of the paragraph implies that there is
sufficient knowledge (data) to suggest that Cryptosporidium is reduced less effectively than
Giardia. This is not the case.
Pages 6-12, Taxonomy, The potential significance of C, bailevi also should be highlighted,
given the recent evidence of human infection (DMeh et al., Parasit. Res., 77:44-47, 1991.).
Page 42, 3rd (last) paragraph. The possibility of other sources of exposure in purported
waterbome outbreaks should be better documented. If such misclassification of exposure
routes or sources of exposure occurs, a tabulation of these outbreaks, giving the different
possible routes of exposure for each outbreak, would be useful.
Page 49, 1st paragraph, 1st sentence. The seasonally of Cryptosporidium, as explained here,
is unclear. Either more detailed and persuasive information must be presented (or cited) or
the issue of seasonality must be left as being inadequately characterized in the U.S.
Page 55, Quantitative Risk Assessment. The coverage and treatment of the infectious dose
aspects of Cryptosporidium are much too limited. If there are inadequate dose-response data
to determine the size of an infectious dose corresponding to a certain risk of infection, this
should be clearly stated. Additionally, the need for such data from humans and other
animals should be emphasized as a gap in essential scientific information and hence, a
research need.
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If there are greater risks (of infection and death) to immunocomproinised hosts, as is stated
later in this paragraph, than what is the effect of immunosuppression or immunodeficiency on
dose-response relationships for Cryptosporidium?
Page 57, 1st paragraph, last sentence. What is the basis for saying that the southeastern
U.S. has a greater risk of waterborne cryptosporidiosis? No documentation is provided for
this statement.
Page 57, 2nd paragraph, last 2 sentences. No substantive and quantitative documentation are
provided for the statements on the risk of exposure to Cryptosporidium from filtered water
supplies, the expected 2 log removal by filtration, the evidence that surface waters contain
"high" levels of oocysts (either spatially or temporally) and that" .... approximately 134
million additional people are at risk of exposure". If this represents some sort of quantitative
or even qualitative risk assessment, it must be better documented. Otherwise, the statements
are not justified on the basis of the scientific data or analyses presented.
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ENVffiONMEOTAL PROTECTION AGENCY
SCIENCE ADVISORY BOARD
DRINKING WATER COMMITTEE
CHAIRMAN
Dr. Verne A. Ray, Medical Research Laboratory, Pfizer Inc., Groton, Connecticut
VICE CHAIRMAN
Dr. Vera L. Snoeyink, Department of Civil Engineering, University of Illinois, Urbana,
Illinois
MEMBER/CONSULTANTS
Dr. Richard J. Bui, College of Pharmacy, Washington State University, Pullman,
Washington
Dr. Gary P. Carlson, Department of Pharmacology and Toxicology, School of Pharmacy,
Purdue University, West Lafayette, Indiana
Dr. Keith E. Cains, East Bay Municipal Utility District, Oakland, California
Dr. Lenore S. Qeseeri, Rensselaer Polytechnic Institute, Materials Research Center,
Troy, New York
Dr. DavM G, Kaufman, Department of Pathology, University of North Carolina, Chapel
Hill, North Carolina
Dr. Ramon G. Lee, American Water Works Service Company, Voorhees, New Jersey
Dr. Edo D. PeHizzari, Research Triangle Institute, Research Triangle Park, North
Carolina
Dr. Mark D. Spbsey, Department of Environmental Sciences and Engineering, School
of Public Health, University of North Carolina, Chapel Hill, North Carolina
Dr. James M. Symons, Department of Civil and Environmental Engineering, University
of Houston, Houston, Texas
Mr. A. Robert Haak, Assistant Staff Director and Acting Designated Federal Official,
Science Advisory Board (A-101F), U.S. EPA, 401 M Street, SW, Washington, DC 20460
Mrs. Frances Dolby, Staff Secretary, Drinking Water Committee, Science Advisory
Board (A-101F), U.S. EPA, 401 M Street, SW, Washington, DC 20460
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NOTICE
This report has been written as a part of the activities of the Science Advisory Board, a
public advisory group providing extramural scientific information and advice to the
Administrator and other officials of the Environmental Protection Agency. The Board is
structured to provide balanced, expert assessment of scientific matters related to problems
facing the Agency. This report has not been reviewed for approval by the Agency and,
hence, the contents of this report do not necessarily represent the views and policies of the
Environmental Protection Agency, nor of other agencies in the Executive Branch of the
Federal government, nor does mention of trade-names or commercial products constitute a
recommendation for use.
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