Risk assessment model for a waterborne outbreak of cryptosporidiosis

摘要

Counts of Cryptosporidium oocysts in 100L volumes of treated water are simulated for conditions representative of a waterborne outbreak in a surface water-derived supply. Assuming oocysts act independently during infection, the risk of infection is directly related to the arithmetic mean oocyst density in the water supply, which is in turn related to the total number of oocysts which break through treatment. Spatial/temporal heterogeneity of oocyst concentrations in the treated water contributes to monitoring programmes based on "spot-sampling" underestimating the arithmetic mean oocyst density and hence the risk of infection. This could contribute to the reported lack of a clear association between oocyst concentrations measured in drinking water supplies and the risk of waterborne outbreak of cryptosporidiosis in the population. An increase in spatial heterogeneity of oocysts during treatment could also contribute to an overestimation of the net oocyst removal by treatment. [References: 11]