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Cryptosporidium (part 2 of 2) Page 6 of 11 <br /> �. f3-28 <br /> a000 <br /> :■r.a�►ywa«�,r� <br /> �b C�rtf�sis <br /> $�[I n 5hiqek►�: <br /> � �asporicfiosis <br /> � 6�0 <br /> � <br /> � <br /> c� <br /> � �00 <br /> �00 <br /> .D <br /> 1989 "1990 1�9�1` 199� ''T993 �1� 'I� `199� 1997 <br /> Y.ear <br /> Figure;b <br /> Infecti4us Disea�e 3n �an Frart�iscc <br /> Research Needs <br /> There are many unanswered questions concerning Cryprosporidium in potable waters <br /> that require investigation. The following are important to San Francisco: <br /> ■ Viability Assessment - Some techniques have been developed in Scotland that <br /> allow viability assessment of detected oocysts. This technique is undergoing <br /> refinement and should be used by San Francisco for assessing Cryptosporidium <br /> viability when it is detected in its source water. <br /> ■ Method Consistencv - Methods for detecting Cryptosporidium in source waters are � <br /> highly variable and results are not readily reproduced within the same lab or <br /> between different laboratories (see Appendix E). Developing new methods that <br /> enabie more consistent and sensitive results is needed. <br /> ■ Method Specificitv - Current detection methods fail to distinguish between species <br /> thought to be responsible for human disease and those that are thought not to <br /> cause disease in humans. Method development is needed to allow that <br /> differentiation. <br /> ■ Infective Dose - While there is some indication that the infective dose for <br /> cryptosporidiosis is very low, it is not known whether different species of <br /> Cryptosporidium have different infectivity (though it seems likely). No information <br /> is available on the infectious dose for an immunocompetent person compared to <br /> an immunocompromised person. However, several ongoing studies may shed light <br /> on these questions. Feeding studies in Scotland with infection-free lambs suggest <br /> that doses as low as 5 oocysts per liter can cause 100 percent infection. A primate <br /> http://sfwater.org/printContent.cfin/C_ID/445/ 10/19/2004 <br />