In 1997, the SFPUC staff were part of a nationwide effort coordinated by the American Water Works Association Research Foundation (AWWARF) entitled Critical Evaluations of Cryptosporidium Research and Research needs. The document outlines a long-term research strategy for the water industry.

Individual agency activities as of December 1992 are summarized in Appendix A. References to Cryptosporidium concentrations are difficult to interpret due to differences in method and sample volume.

San Francisco Public Utilities Commission (SFPUC) Activities

The SFPUC has been aggressively pursuing the issue of Cryptosporidium in the following manner:

• Monitoring - Preliminary monitoring for Giardia and Cryptosporidium was conducted in 1990. This has been followed by an intensive 12-month monitoring program for all sources, both treatment plants, and two distribution system reservoirs. The program has been completed, although some monitoring continues.



• Consultations - A number of meetings have taken place with DHS staff regarding Cryptosporidium. In July 1992, the SFPUC met with health officials from the four Bay Area counties served by the SFPUC to discuss the significance of waterborne Cryptosporidium. In November 1992, SFPUC staff met with four water utilities to discuss their respective programs on Cryptosporidium (Appendix B). In January 1993, the SFPUC convened a workshop with regulatory authorities (i.e., DHS and EPA), public health officials, researchers and medical experts to discuss the incidence of cryptosporidiosis, its relative public health significance, current research, and potential studies to address the major uncertainties (Appendix C). A Bay Area workshop was held in June 1995 to evaluate a disease surveillance program and to discuss risk communication issues (Appendix D). The SFPUC conducted stakeholder interviews to assess public concern and attitudes towards costs of various treatment alternatives in 1995. Findings of these interviews indicated a low public awareness of Cryptosporidium, though high concern among water treatment and public health professionals. In addition, San Francisco supervisor Carole Migden formed a 17 member multi-disciplinary Cryptosporidium task force for the purpose of developing guidelines for public notification of immunocompromised individuals and the general public. Due to a concurrent risk communication effort by a consortium of water utilities and DHS, this committee never completed its work. In late-1996, the SFPUC began regular strategy sessions with the major unfiltered sources in the U.S. (i.e., Boston, New York City, Portland, Tacoma and Seattle).
  
  
• Treatment - The SFPUC is performing an evaluation of its filtration practices at the Harry Tracy and Sunol Water Treatment Plants to optimize particulate removal. Pilot studies at Hetch Hetchy evaluated optimization techniques for Cryptosporidium removal. Disinfection studies were performed at the University of Arizona evaluating the influence of existing physical and treatment conditions in the SFPUC Hetch Hetchy water delivery and treatment system on Cryptosporidium. These included pH changes (SFPUC water is increased from 7 to 10), pressure drops (there are two major powerhouses on the Hetch Hetchy Aqueduct that may rupture the oocysts), and sequential addition of disinfectants. These studies indicated that Cryptosporidium inactivation is currently negligible, but that sequentially adding chlorine followed by chloramine is capable of providing modest inactivation of Cryptosporidium. SFPUC testing showed up to 1 log (or 90 percent) Cryptosporidium inactivation was possible. The required ozone dose for inactivating Cryptosporidium in Hetch Hetchy has been determined to require a much longer reaction time than is conventionally used for ozonation. The risks of stimulating growth of opportunistic bacteria in consumer plumbing remains a concern with this option.



• Watershed Protection - In 1997, the SFPUC engaged in an intensive public process to modify grazing practices in the Alameda watersheds to limit microbial risks. A series of best management practices have now been adopted.

San Francisco Source and Treated Waters

The SFPUC has been intensively monitoring all three of its sources for Cryptosporidium and Giardia since January 1993. Giardia and Cryptosporidium have been detected in a few samples.

For monitoring, two methods have been used at different times. From January 1993 through October 1994, proposed Standard Method 9711B (without differential interferences contrast microscopy) was used. Since November 1994, the ICR method has been used. Using proposed Method 9711B, Cryptosporidium levels detected ranged from less than 0.1 to 0.8 oocysts per 100 liters in Hetch Hetchy water. Cryptosporidium was typically detected in approximately 30 percent of the samples collected.

With the ICR method, presumptive Cryptosporidium levels in Hetch Hetchy water ranged from 0.4 to 7 oocysts per 100 liters, approximately an order of magnitude greater than results obtained using proposed Method 9711B. Oocysts continued to be detected in about 30 percent of samples even though the median detection limit increased from 0.1 to 1 oocyst per 100 liters with the method change. The difference in results appears to be related to method changes rather than environmental changes (i.e., increased watershed contamination). See Appendix E for further discussion on method differences.

Cryptosporidium oocysts were also detected in some samples from San Antonio, Calaveras, and San Andreas Reservoirs (all of which are filtered) and in some finished waters. Three points should be noted. First, detection of oocysts in the treated water does not provide information about viability. There is a high likelihood that oocysts detected in finished waters are not viable.⁵³ Second, due to the small number of samples it is not clear whether these were unusual occurrences (the largest fraction of positive samples were performed by a different lab and collected by different personnel two years ago when methods were less rigorously defined). Third, it is not unusual to detect oocysts in the treated water.² In any case, the implication is clear: efforts should continue to focus on watershed management and treatment process optimization. These results are summarized in Table 2. The distribution of concentrations in Hetch Hetchy water is presented in Figure 3. Figure 4 shows that, despite a summertime increase in the number of positive samples, oocyst concentrations remain low year round. Appendix F contains a summary of Cryptosporidium and Giardia concentration seasonal trends for all of SFPUC source waters.

Infectious Diseases Reported in San Francisco Area

Data from the San Francisco Public Health Department (see Figure 5) indicates that over the past 7 years the incidence of reported cryptosporidiosis cases has ranged from 38 in 1989 (when monitoring began) to 144 in 1991 corresponding to a risk of 1 in 5,000. This compares with roughly 400 giardiasis cases, 200 salmonella cases, 300 shigella cases, and 700 campylobacter cases (all of which are treatable). Most of the San Francisco Cryptosporidium cases are attributed to AIDS patients and are not thought to be water related. The county environmental health officers of Alameda, San Francisco, San Mateo, and Santa Clara believe that cryptosporidiosis from drinking water is not a major concern.

A preliminary epidemiological assessment was conducted by the Community Disease Control Program of the City and County of San Francisco. Five hundred and thirty three (533) cryptosporidiosis cases were segregated according to areas served by filtered and unfiltered water. The incidence of cryptosporidiosis was four times higher in the filtered area than in the unfiltered area. Even though this study was biased towards males and patients with AIDS, it did not uncover an association between unfiltered Hetch Hetchy water and cryptosporidiosis. Further work would need to be done to assess the importance of unfiltered Hetch Hetchy water. The indications from this preliminary study, however, is that there is no "smoking gun" pointing to unfiltered Hetch Hetchy water.

Research Needs

There are many unanswered questions concerning Cryptosporidium in potable waters that require investigation. The following are important to San Francisco:

• Viability Assessment - Some techniques have been developed in Scotland that allow viability assessment of detected oocysts. This technique is undergoing refinement^9,31 and should be used by San Francisco for assessing Cryptosporidium viability when it is detected in its source water.



• Method Consistency - Methods for detecting Cryptosporidium in source waters are highly variable and results are not readily reproduced within the same lab or between different laboratories (see Appendix E). Developing new methods that enable more consistent and sensitive results is needed.



• Method Specificity - Current detection methods fail to distinguish between species thought to be responsible for human disease and those that are thought not to cause disease in humans. Method development is needed to allow that differentiation.



• Infective Dose - While there is some indication that the infective dose for cryptosporidiosis is very low, it is not known whether different species of Cryptosporidium have different infectivity (though it seems likely). No information is available on the infectious dose for an immunocompetent person compared to an immunocompromised person. However, several ongoing studies may shed light on these questions. Feeding studies in Scotland with infection-free lambs suggest that doses as low as 5 oocysts per liter can cause 100 percent infection. A primate study in Kenya will soon be finalized. Initial results have been ambiguous since low oocyst doses induced disease in some primates while higher doses failed to produce any illness in other primates (maybe due to acquired immunity). A human feeding study in Texas evaluating the infectivity of various Cryptosporidium oocyst doses found 20 percent of the subjects were infected at the lowest dose (30 oocysts). A joint University of California at Davis and University of California at San Francisco study will evaluate the infective oocyst dose for immunocompromised primates to provide information on the minimum infective dose for immunocompromised populations.



• Relative Exposure - It is unclear how much of the cryptosporidiosis risk can be attributed to drinking water. Work is vitally needed that distinguishes the water contribution to cryptosporidiosis from other sources. This will enable better risk management and more efficient resource allocation.



• Communication of Uncertainty - Issues associated with detection, species differentiation, viability, infectivity, host susceptibility, compel the uncertainty associated with cryptosporidiosis risk in drinking water. Better methods are needed for quantitatively characterizing this uncertainty and communicating it in a manner that is comprehensible to the public and aids them in making their own personal risk management decisions.



• Chemical Inactivation - Further work needs to be done to evaluate the impacts of chlorine on environmentally-stressed oocysts which may be more susceptible to chlorine inactivation than fresh oocysts. The impact of sequencing disinfectants (e.g., chlorine followed by chloramine) needs to be evaluated further so as to refine the available alternatives for the SFPUC with regards to disinfection by-products.



• Filtration - While some preliminary work has been conducted on the removal of Cryptosporidium in water treatment processes, more is needed on the influence of filter media and filtration rates. An assessment of the importance of increased parasite loading during the backwash water operations such as recycling, and flow rate changes needs to be made. Work on Cryptosporidium removal is being completed under the auspices of AWWARF and by the British Drinking Water Inspectorate.

Current Action Plan

The SFPUC action plan is focused on providing information that will aid in the assessment and control of the risks associated with Cryptosporidium.

• Monitoring - SFPUC will continue its monitoring program for its major sources and start to monitor treated water samples in addition to the existing distribution system locations. The sample volumes have been increased to lower the detection limits.



• Treatment Process Evaluation - The two SFPUC filtration plants already conform to the recommendations of the Badenoch report and the Surface Water Treatment Rule. Nevertheless, an evaluation of operating practices (e.g., increasing plant flows, treating high turbidity water, washwater handling, etc.) is planned to determine how plant operations can adapt to adverse conditions and protect against parasite breakthrough. Major upgrades are under design at our Sunol Valley Water Treatment Plant.



• Watershed Sanitary Survey - A comprehensive watershed survey has been conducted which (1) identifies the origin of the Cryptosporidium oocysts (i.e., sampling major tributaries into reservoirs, camping areas, septic tanks, stables, etc.), (2) evaluates the transport and fate of the oocysts, and (3) determines the degree to which the oocyst sources can be controlled. The recommendations for watershed management are under development.



• Risk Communication - The SFPUC is developing an education plan for presenting information on risks and mitigative measures to sensitive populations.

These four activities are planned for completion by the end of 1998.

Possible Future Studies

In addition to the studies currently being conducted by the SFPUC, the following studies will also be valuable:

• Exposure Assessment - If a current seroprevalency research project examining the contributions of water to the degree of exposure of a population proves successful, it would be advisable for San Francisco to conduct similar studies to ascertain the contribution of exposure unfiltered water presents to the various affected populations. This may be the key piece of data needed to determine the relative significance of water in cryptosporidiosis cases.



• Improved Sample Method Development - In light of the importance of Cryptosporidium and the SFPUC's current unfiltered status, it may be prudent to join in efforts to further development of Cryptosporidium detection methods.



• Assess Willingness to Pay - Since some populations are more impacted than others, it may aid policymakers to quantify the amount various individuals are willing to pay for different treatment improvements (e.g., ozonation, filtration, and point of use devices). Such determinations need to use the rigorous methods developed in survey research.



• Molecular Epidemiological Studies - Using recently developed methods, it should be possible to type and subtype Cryptosporidium parvum isolates. This will allow matching of the organism shed by the infected person and the source of the organism. To address the waterborne route, SFPUC needs to start collecting and storing water samples until a case of cryptosporidiosis is reported. Once the organism from the infected person is isolated and typed, an attempt could be made to match this to an organism found in the stored water samples. If a positive match is made, this would implicate the water route. If the organism matched that from a pet, a member of a family, etc., then these would be the suspected routes of infection. Such a study would provide definitive answers to whether there is a link between the drinking water and cryptosporidiosis.

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