Dose response assessment
Dose Response Models
Dose response models are necessary as it is not possible to perform a direct study (even with animals) to assess dose corresponding to an acceptably low risk. A dose response is used model to interpolate or extrapolate to low dose.
To be plausible a model should consider the discrete (particulate) nature of organisms, which has a high variability at low dose. It should also be based on the concept of infection from one or more “survivors” of initial dose.
Types of Models
Exponential Dose Response Model
Assumptions:
- Poisson distribution of organisms among replicated doses (mean number in dose=d).
- One organism is capable of producing an infection if it arrives at an appropriate site.
- Organisms have independent and identical probability of surviving to reach and infect at an appropriate site (k).
p = 1 - exp^{(-kd)} |
Beta-Poisson Model
Assumptions same as the exponential model except,
- Nonconstant survival and infection probabilities
- Survival probabilities (k) are given by the beta distribution
Slope of dose response curve more shallow than exponential
Besides dose response assessment, the other major components of microbial risk assessment are hazard identification, exposure assessment, and risk characterization.