Animal Waste, Water Quality and Human Health

392Animal Waste, Water Quality and Human HealthAPPENDIX: BASIS OF VALUES PRESENTEDIN TABLE 10.1This appendix provides an explanation and reference to published literature for valuespresented in Table A10.1, which describes characteristics of the selected microbialhazards relevant to the risk they pose to people exposed to recreational waterscontaminated by them.ID 50 VALUESID 50 values are taken from best-estimate dose-response relationships as reported in theliterature. No explicit account is taken of uncertainty, though that is often desirable inparticular quantitative risk assessments (Teunis 2009).CAMPYLOBACTERIOSISThe two parameters for the beta-Poisson dose-response curve were derived by Medemaet al. (1996), using data for healthy urban adult volunteers reported by Black et al.(1988). This curve, for probability of infection given an average dose, is givengenerally by Pr infection =1–(1 + d/β) −α , where d is the average dose given to eachgroup of volunteers, α is a shape parameter and β is a scale parameter. Theyobtained the parameter values as α = 0.145, β = 7.589, from which ID 50 (forinfection) = β(2 1/α –1) ≈ 897 (see also Teunis & Havelaar 2000). Teunis et al. (2005)later analysed campylobacteriosis rates among two sets of children at school camps,which indicated an ID 50 (for illness) < 10. In other words, even in developedcountries children exhibit markedly higher rates of campylobacteriosis than is thecase for adults (see also Rao et al. 2001).E. COLI O157:H7 INFECTIONTeunis et al. (2008) analysed several outbreaks for illness using the two-parameterbeta-Poisson dose-response model and obtained prediction parameters for theheterogeneous case (α = 0.248, β = 48.80), which results in ID 50 (for illness) ≈ 750.SALMONELLOSISHaas et al. (1999) analysed infectivity of Salmonella (non-typhoid strains) in humanvolunteers in studies reported by McCullough and Eisele (1951a&b), obtaining ID 50= 23,600. A more recent study (Bollaerts et al. 2008) has analysed a larger set ofdata which generally suggests lower ID 50 values, particularly for the “susceptible”component of a population (see also Blaser & Newman 1982 and Rose & Gerba 1991).