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Risk assessment for Cryptosporidium: a hierarchical Bayesian analysis of human dose response data.
M J Messner1, C L Chappell, P C Okhuysen
1USEPA Office of Ground Water and Drinking Water, Washington, DC 20460, USA. messner.michael@epa.gov
Water Research
|September 17, 2002
Summary
This study quantifies the infectious dose of Cryptosporidium parvum strains, revealing significant differences in infectivity. These findings are crucial for understanding and assessing the risk of cryptosporidiosis outbreaks.
Area of Science:
- Infectious Diseases
- Parasitology
- Public Health
Background:
- Cryptosporidium parvum is a significant cause of diarrheal disease globally.
- Previous studies determined median infectious dose (ID50) using limited definitions of infection.
- Understanding dose-response relationships is vital for risk assessment.
Purpose of the Study:
- To re-analyze Cryptosporidium parvum dose-response data using a broader definition of infection.
- To estimate the ID50 for different C. parvum isolates (IOWA, TAMU, UCP).
- To evaluate the utility of these results for probabilistic risk assessment.
Main Methods:
- Dose-response studies with healthy volunteers using three C. parvum isolates.
- Analysis using a broader infection definition: oocysts in stool and/or diarrheal illness.
- Application of maximum likelihood and hierarchical Bayesian models for parameter estimation.
- Markov Chain Monte Carlo analysis for posterior distributions.
Main Results:
- Maximum likelihood estimates for UCP, IOWA, and TAMU were 2980, 190, and 17.5, respectively.
- ID50s were calculated as 2066, 132, and 12.1 for UCP, IOWA, and TAMU isolates.
- Bayesian analysis yielded similar dose-response parameter estimates.
- Estimated risks of infection from single oocyst doses ranged from 0.018 to 0.028.
Conclusions:
- Significant variations exist in the infectious dose of C. parvum isolates.
- The study provides robust estimates for probabilistic risk assessment of cryptosporidiosis.
- Findings contribute to better public health strategies for preventing C. parvum infections.