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C:ryptosporidium (part 2 of 2) Page 7 of 11 �.6-2q study in Kenya will soon be finalized. Initial results have been ambiguous since low oocyst dpses induced disease in some primates while higher doses failed to produce any iliness in other primates (maybe due to acquired immunity). A human feeding study in Texas evaluating the infedivity of various Cryprosporidium 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. ■ Re/ative 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 Uncertaintv - 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. ■ Chemica/ 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. ■ Monitorina - 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 http://sfwater.org/printContent.cfin/C_ID/445/ 10/19/2004 r _ .r.