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CryptosporidIum (part 2 of 2) Page 3 of 11 i.6-25 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. Table 2 Summary of SFPUC Parasite Monitoring Results 1993-1996 I Giardia II Cryptosporldlum I ~ Avg. Avg. I~~I Avg. Avg. Location Year Detection Detection Concentration Concentration Limit Limit (Per 100 L) (Per 100 L) (Per 100 L) (Per 100 L) 1199311 17 0.3 0.15 II 35 II 0.2 0.15 1199411 30 1.8 0.7 II 26 II 1.1 0.7 Hetch Hetchy 1199511 35 2.2 1.2 II 24 II 1.5 1.2 1199611 34 1.7 1.1 II 12 II 1.2 1.1 r----ï, II II http://sfwater.orglprintContent.cfin/C_ID/445/ 10/19/2004 r T