Risk assessment of waterborne Cryptosporidium

Victoria Norma Ochoa, University of Texas at El Paso


In an effort to update the risk assessment of waterborne Cryptosporidium an additional and more complete human dose-response dataset of the parasite was used to calculate the risk of infection. The complete data studied contains larger human outcomes than the initial prior risk assessment evaluated by Haas et. al. in 1999. Quantitative analysis of the complete dose-response indicates that it no longer follows the Exponential Model used to estimate the risk for the initial data. The complete dataset appears to provide a better fit with the Beta-Poisson Model and even a dose independent constant risk model, which shows a considerable higher risk than the one previously calculated for the initial work. A comparative examination between the complete exponential, initial exponential and complete Beta-Poisson risk analysis is presented on this study including a recommended water treatment level based upon the complete dataset. Employing Quantitative Microbial Risk Assessment (QMRA) the complete Beta- Poisson dataset results and the Milwaukee outbreak of 1993 were compared, and the results observed produced an excellent agreement with the outbreak outcomes. The impact of immune status was incorporated to the study in order to determine a possible reduction of human health risks associated with waterborne Cryptosporidium. The antibody status in the study volunteers' and the type of isolate strain used in the human exposure are confounding factors that complicate the risk assessment. Antibody status was found to significantly influence infection rates. The type of isolate appears to be important but the dataset is too small to discern clear differences. In addition, an annual comparative risk assessment examination between the complete constant, complete Beta-Poisson, and initial exponential risk analysis is presented on this study; which reflects and reinforces the existence of a higher risk when complete constant and complete Beta-Poisson models are employed in an order of 100 times greater risk than initial exponential model.

Subject Area

Environmental science

Recommended Citation

Ochoa, Victoria Norma, "Risk assessment of waterborne Cryptosporidium" (2014). ETD Collection for University of Texas, El Paso. AAI3623448.